The Complete Human Body Dr Alice Roberts

399

DEVELOPING EMBRYO

DEVELOPMENT OF THE PLACENTA

The placenta develops from the outer matter such as bacteria in maternal blood,
layer of the blastocyst—the ball of cells while being a membrane across which it can
that results when the sperm fertilizes the bring in nutrients and oxygen from maternal
egg. The placenta has several functions. blood and expel waste products. It also
It provides a barrier to protect the baby produces hormones essential for the
from harmful substances and even foreign continuation of the pregnancy.

1 Trophoblast proliferates Maternal Maternal
The outer layer of blastocyst cells
become the trophoblast, which taps into the Maternal vein artery blood sinus
blood vessels of the maternal endometrium.
This forms the placental bed across which Endometrium
nutrients and oxygen cross into the fetal Trophoblast
blood system and waste products flow out.
Embryonic cells
2 Chorionic villi form
The flat trophoblastic layer develops Maternal
fingerlike projections, called chorionic villi, blood sinus
growing out into the tissue of maternal blood
sinuses to increase the surface area and Chorionic villus
augment nutrient transfer. Fetal blood vessels
then grow into the chorionic villi. Fetal vein
Fetal artery
3 Placenta established
By the fifth month, the placenta has Uterus lining All the basic organs have formed Cocooned fetus
become established, with a large network of and the skeletal cartilage starts An 8-week-old fetus is shown
villi protruding deep into maternal blood-filled Maternal blood to turn into bone. Spontaneous suspended by the umbilical cord
chambers called lacunae. After implantation chamber movements are occurring. within an intact amniotic sac.
the placenta produces the human chorionic The shriveled yolk sac (red) can
gonadotropin (hCG) hormone. Chorionic villus be seen separately to the right,
hanging from the placental root
Blood vessels of the umbilical cord.

Prominent Nostrils appear Digits beginning to Ears have started Mouth and lips nearly Head has lifted
forehead bulges as as shallow pits form on hands to develop fully developed off chest
and feet
brain develops Outer ear
Nose protrudes fully formed
Shrinking from face
yolk sac

Established Lengthening Elbows now Wrist has
placenta limb buds visible formed

Limb development Structural details Basic human shape
The embryo starts to show a recognizably human form At 1 in (25 mm) long, the embryo is growing rapidly and its Now 11/2 in (40 mm) long, the embryo has an obvious human
as the limb buds develop and lengthen and the early “tail” is finer structural detail is forming. By 6 weeks, the hands will have shape, including a recognizable face and even the early detail
reabsorbed. Neural tissue rapidly evolves into specialized formed fingers, the feet will have developed toes, and the basic of fingerprints. All the basic internal organs have formed and
sensory areas, such as the eye and the cochlear structure of the eyes will have differentiated into structures including a lens, the skeletal cartilage starts to develop into bone. Spontaneous
inner ear. An increasing amount of nutrition now comes via the retina, and eyelids. Electrical brain activity is established and movements are occurring. After the end of the 8th week,
placenta as the yolk sac starts to shrink. sensory nerves are developing. the embryo is referred to as a fetus.

5 WEEKS 6 WEEKS 8 WEEKS

400

LIFE CYCLE

FETAL
DEVELOPMENT

From 8 weeks until delivery, the fetus grows rapidly
in size and weight. During this time, its body systems
develop and evolve until it has reached a stage when
it is sufficiently mature to sustain itself once separate
from its mother after birth.

THE GROWING BABY developed countries (less Fetus at 20 weeks
in developing countries,
By the time an embryo has become a fetus, it has where maternal health can on the organs gaining size, The skin is coated in a greasy
developed a clearly human form. From this point, be less certain). Growth will body length, and structure, substance called vernix, which
measuring 1in (2.5 cm) long or roughly the size of a grape, depend on many factors, while fat deposition occurs protects it from prolonged
including maternal health, nutrition and lifestyle, fetal later. Bones grow by cell contact with amniotic fluid.
it has 32 weeks to grow or placental disease or abnormalities, and also ethnic or
to an average birth familial trends in size and weight. Generally, the fetus is division from the growth plates at either end of the long
weight of around protected from minor or transient maternal illness, but
6½–83/4 lb (3–4kg) in more serious illnesses can affect its growth. Initially floating bones. Specialized cells of the nervous system, such as
free in the amniotic fluid, as the fetus grows its movement
Fetus at 12 weeks becomes increasingly restricted until it fills the stretched the retinal cells, become more refined and the brain cells
Ultrasound imaging shows uterine cavity. During the early period, growth is focused
the fetal heartbeat, spine, gather detailed information as sensory input increases.
limbs, and even recognizable
details such as facial features.

Eyes have moved to Body has no Greater hand mobility In the brain, nerve cells In girls, ovaries have Fingernails have
the front of the face, underlying fat means that the baby is are growing from descended from the started to grow
and bones appear able to suck its thumb central to outer areas abdomen to the pelvis
but remain closed prominent

Limbs are
lengthening

rapidly

Toes have Gut can take in Skin covered with fine
separated small amounts of hair, called lanugo,
and greasy vernix
amniotic fluid

Developing sensation Sucking, breathing, and swallowing Making its presence felt
Weighing around 1½ oz (45 g) and measuring 3½ in (9 cm) By this stage, the fetus has developed a swallowing action and At 6 in (15 cm) long and weighing 11–14 oz (300–400 g), the
long, the fetus is now active and is able to stretch out and test will ingest amniotic fluid, which is then absorbed by the body. fetus is highly active and the mother begins to feel fluttering
its muscles. Its eyes are shut but the brain and nervous system The kidneys are functioning, cleansing the blood and passing sensations through the uterine wall. (The top of the uterus can
are both sufficiently developed for the fetus to sense pressure urine back into the amniotic fluid via the bladder and urethra. now be felt above the pubic bone.) Unique fingerprints are
on its hands and feet, and it can open and close its fists and Breathing movements are occurring and the fetus will have now fully established on the fingers and toes of the fetus, and
curl its toes in response to such stimuli. discovered its mouth with its hands and may suck its thumb. its heart and blood vessel systems are fully developed.

11 WEEKS 14 WEEKS 19 WEEKS

401

FETAL DEVELOPMENT

HOW THE PLACENTA WORKS Uterine muscle CONNECTED AND NOURISHED

The placenta supplies the growing fetus with nutrients, such Maternal blood vessels The 6 in- (15 cm-) long umbilical cord connects the
Flow of wastes blood vessels of the placenta to the blood system of the
as glucose, amino acids, minerals, and oxygen, and removes Fetal blood vessels fetus, allowing the flow of nutrients and return of waste.
Maternal blood in Unlike most adult blood vessels, the umbilical vein
waste products such as carbon dioxide. It does this by acting intervillous space supplies oxygenated blood and nutrients, while the two
Flow of nutrients arteries carry deoxygenated blood and waste products to
as a barrier between adjacent maternal and fetal blood flows, the placenta. Abnormalities of the cord, such as being
Exchange of nutrients unusually short, long, or having only one artery, are
allowing these molecules to cross while protecting the fetus Nutrient and waste exchange
occurs across the walls of the associated with a
from maternal waste, variation in her metabolism, and placental blood vessels. variety of fetal
malformations. The
bacteria. The placenta secretes hormones, including estrogen, Inner ear organs have cord has few sensory
matured enough to send nerves and is clamped
progesterone, and human chorionic gonadotropin (hCG). Umbilical nerve signals to the brain and cut after birth.
cord
Maternal antibodies can cross the placenta in late pregnancy, Umbilical lifeline
Direction of The blood vessels of the
giving the fetus passive immunity to infections, blood flow umbilical cord are protected
to the fetus and insulated within a
but the placenta also has several mechanisms Direction of gelatinous substance called
to keep the mother’s immune system from blood flow Wharton’s jelly.

recognizing the fetus as foreign and attacking it. from the fetus

Hands are very
active, touching the

face, body, and
umbilical cord

From 22 weeks, the fetus
begins to stand a small but
increasing chance of survival
should it be born prematurely.

The nerve cells that Eyelids have not
make up the outer yet started to open
surface of the brain

are in place

Fluid-filled lungs are
not quite ready for
the outside world

A chance of survival Every bone in the body Layers of body fat are being Responsive to sound and motion
From 22 weeks, the fetus begins to stand a small but increasing now contains bone stored beneath the skin; fats Surrounded by constant maternal internal noise—heartbeat,
chance of survival should it be born prematurely. Most body contribute to the development bloodflow, and intestinal gurglings—the fetus is responsive to
systems are sufficiently developed to cope with independence marrow, which produces of the nervous system external noise or movement, quickening its heartbeat and
from the mother, although the biggest problem at this stage red blood cells increasing its own movement (felt by the mother as “kicks”),
would be with the respiratory system. Although the breathing or, conversely, slowing when soothed. Now with developed
reflex is in place, the lungs are not yet fully mature. balance mechanisms, it is aware of positional change.

22 WEEKS 25 WEEKS

402

LIFE CYCLE

TOWARD FULL TERM called meconium (comprising amniotic fluid, skin cells, BREAKTHROUGH
lanugo hairs, and vernix) that is not usually passed until
Development during the final 3 months is mostly a delivery. (However, if the fetus becomes stressed, for MIRACLE BABIES
process of consolidation as the fetus’s organs have all example by falling oxygen levels, some meconium may
formed but need to mature. The fetus continues to refine get passed into the amniotic fluid.) The fetus is rapidly The increasing availability of high-level medical care for
its various activities and functions, including movement, gaining fat stores, and its growing lungs will have reached premature, small, or sick newborns means that survival rates
breathing, swallowing, and urination. The bowels show a stage of maturity at which they may be able to cope have drastically improved; even babies born at 22–23 weeks
rhythmical activity, but contain a plug of sterile contents with breathing if premature delivery occurs. now have a good chance of a healthy life. All aspects of
neonatal care, including respiratory assistance, intravenous
Sensations become more acute—the eyes (already fluids and medicine, and feeding via a tube, support the
detecting simple light levels) will open, the ears pick up newborn until it is strong enough to be cared for as any
familiar sounds—and the fetus displays a sense of its normal baby. Monitoring aids such as electrocardiograms,
surroundings and also of the state of its mother. If the oximeters (which measure oxygen levels in the blood), and
mother relaxes, increasingly the fetus will too; if she is venous or arterial access points for blood sampling are
anxious or restless, it will respond to this. essential tools in stabilizing their condition.

Fetus at 26 weeks Special care baby unit
This 4D ultrasound image gives an all-round view of Incubators are thermostatically controlled and highly
the fetus, showing head, torso, and limbs together with equipped to monitor a premature, low-weight, or sickly
the umbilical cord and placenta. When the baby baby’s heart rate, blood pressure, fluid and oxygen levels,
moves (time being the 4th dimension), its movement breathing, and other bodily functions.
and structural development can also be assessed.

Brain waves revealing electrical
activity have been detected from
6 weeks, and by 26 weeks rapid
eye movement sleep occurs—
usually associated with dreaming.

Blood flow through the Eyelashes and Creases can be Increased fat Pupils of the eyes are The enzymes in the
umbilical cord regulates eyebrows are growing seen in the skin of layers have able to dilate in response baby’s gut are active,
the baby’s temperature thicker and longer the wrists and the rounded out the meaning it would be
palms of the hands baby’s body to light filtering through able to process food
to the baby

Skin looks
pinker and less

translucent

Changing eyes Maturing lungs Skin changes and space restrictions
Measuring 13 in (33 cm) long and weighing around 2 lb (850 g), The heart rate will have begun to slow slightly from its At a weight of about 4lb (1.9kg), increased fat deposition
the fetus has full sets of eyelashes and eyebrows, but will not previous rate of 160 beats per minute (bpm) to 110–150 bpm. fills out early wrinkles. The vernix and lanugo will begin to
open its eyes for another week or two, when the upper and The cells that line the lungs are by now starting to secrete a disappear and the skin loses it translucency. The fetus wriggles
lower lids have separated. The initial eye color will be blue, substance (surfactant) that will help them to inflate when the but there is little space for vigorous movement. Its eyes blink
as true pigmentation does not occur until later, often baby takes its first breath. In boys, the testes will have moved and breathing movements may result in hiccoughs—harmless
not until after the birth. down from the abdomen and will descend into the scrotum. spasms of the diaphragm.

26 WEEKS 30 WEEKS 35 WEEKS

Ready for birth
By 40 weeks, the baby’s organs are
mature, and it now fills the entire
uterine space. It is ready to leave the
womb and face the outside world.

404

LIFE CYCLE

THE NEWBORN

The first four weeks of a baby’s life, known as the neonatal period, are a time of immense
change and adaptation. This is also one of the most dangerous stages of life, with a higher
risk of death than at any other time until retirement age.

STARTING OUT IN THE WORLD Fontanelle Baby skeleton
Flexible, fibrous joint A newborn’s skeleton is soft
At birth a baby has a head that is large in proportion to its body, and often misshapen between skull bones; and flexible, with immature
due to molding of the skull during passage through the birth canal. The abdomen is bones largely composed of
relatively large, with the appearance of a pot belly, whereas the chest is bell-shaped and fontanelles allow cartilage. Gradual hardening,
about the same diameter as the abdomen, so it appears small. The breasts may be changes in skull called ossification, will take
swollen as a result of maternal hormones, and sometimes a pale, milky fluid leaks out. shape, allowing the place throughout childhood
baby to pass through until the full adult skeleton of
Most newborn babies appear somewhat blue, but turn the birth canal 206 solid bones is complete.
pink as they start to breathe. Some have a fine covering of
pale, downy hair called lanugo, which will disappear Jaw
within a few weeks or months. More than 80 percent of Contains fully
babies have some kind of birthmark, an area of pigmented formed
skin that usually fades or disappears as the child gets older. primary teeth
that do not
Skin protection Thymus gland erupt until the
At birth a baby’s delicate new skin Part of the immune baby is about
is protected by a waxy, cheeselike system, it is large at birth 6 months old
coating known as vernix caseosa, because the immune
formed from skin oils and dead cells. system is maturing rapidly Lungs
With the first breath,
SIGN SCORE: 0 SCORE: 1 SCORE: 2 Heart the baby’s lungs fill
HEART RATE Changes in structure at with air and expand;
None Below 100 Over 100 regular breathing
birth enable blood to then begins
BREATHING RATE None Slow or irregular; Regular; circulate through the lungs
Intestines
weak cry strong cry rather than the placenta Excrete the first fecal
material as a thick,
MUSCLE TONE Limp Some bending Active Liver Pelvis sticky, greenish black
of limbs movements Relatively large at birth Primarily made mixture of bile and
REFLEX None so it protrudes below the of cartilage at mucus called
RESPONSES Grimace or Cry, sneeze, birth, it hardens meconium
whimpering or cough rib cage to bone during
childhood Genitals
Apgar score Large in both sexes;
A newborn baby’s health is assessed at girls may have a slight
one minute and five minutes after birth, vaginal discharge
based on five characteristics. A perfect
COLOR Pale or blue Blue extremities Pink score is 10. A score of 3 or less shows the
baby needs immediate resuscitation.

Just arrived
In developed countries the average
weight of a newborn baby is 71/2 lb
(3.4 kg) and the average length, from
crown to heel, is 20 in (50 cm).

405

THE NEWBORN

CHANGING CIRCULATION CUTTING THE CORD

While in the womb and unable to breathe or eat for itself, the fetus receives Unless it has already been cut, the umbilical
nourishment and oxygen, via the umbilical cord, from the blood flowing through the cord will continue to pulse for up to 20
placenta, and gets rid of waste products, including carbon dioxide, in blood flowing minutes after a baby is born, maintaining
back to the placenta. The fetal circulation is adapted to make this arrangement work by the baby’s oxygen supply and keeping the
having specialized blood vessels that convey blood to and from the umbilical cord and placental blood supply flowing until it is no
enable most of the blood to take a route that bypasses the immature liver and lungs. longer needed. After this, the cord can be
At birth, the lungs start to inflate with the first breath, causing pressure changes that safely clamped or tied and cut—this is
increase blood flow through the lungs and close off these special channels. The baby painless because there are few nerves in the
has made the transition to breathing air. cord. At birth, the average umbilical cord is
about 20in (50cm) long and usually a
Fetal circulation Blood supply stump 1–11/2in (2–3cm) long is left attached Umbilical stump
Oxygen- and nutrient-rich to upper body to the baby’s umbilicus. The placenta will The umbilical stump will gradually shrivel and
blood is supplied through the Ductus arteriosus allows be expelled naturally around 20 minutes to dry out. It will fall off by itself in 1 to 3 weeks,
placenta, and deoxygenated umbilical blood to an hour after the baby is born, although this leaving a “belly button” that may be inverted
blood containing waste bypass lungs may be accelerated by an injection given or protrude outward.
products flows back through Left atrium during the birth. Meanwhile the baby can
it to be enriched again. Left lung be put to the breast.

Blood supply from Heart FOOD FOR LIFE
upper body
Descending aorta A newborn baby instinctively attempts to find its mother’s breast and suckle. Thanks to
Pulmonary artery an automatic response called the rooting reflex, babies turn their head toward a touch
Inferior vena cava on their cheek or lips and make sucking motions. If put to the breast, the mouth will
The foramen ovale, a automatically open and the baby will latch on, taking the whole areola into its mouth,
window between atria, Umbilical arteries and begin to suck. After a few seconds, the mother’s let-down reflex comes into play and
is a short-cut for blood take waste products and
passing from placenta deoxygenated blood milk starts to flow. Sweet, pre-milk
back to placenta colostrum helps guard against infection
to fetus and contains beneficial “good bacteria” to
protect the baby’s immature gut. Breast
Ductus venosus milk proper is nutritionally ideal and
connects umbilical vein contains antibodies that defend against
infection. Breastfed babies are also less
to inferior vena cava likely to develop allergies later in life.

Umbilical vein carries all Suckling instinct
nourishment and The suckling instinct is strongest for about half an
dissolved gases hour after birth, when feeding also stimulates
maternal hormones that help the uterus to
Placenta links blood Blood supply to lower contract down and the placenta to be expelled.
supplies of mother body
and baby LIFE OUTSIDE THE WOMB

Blood supply from Ductus arteriosus Most newborn babies sleep for much of the day and night, but wake to feed every
upper body closes few hours. An average baby will cry for between 1 and 3 hours a day. Within the first
Increased blood flow 24 hours a baby should urinate and have a first bowel movement, although for the first
Pulmonary to lungs few days this will be meconium, a green-black, sticky substance representing the fetal
veins bowel contents. Once the baby is settled into a feeding routine, its stools will become
More oxygen-rich grainy and brown, then yellowish. In the
Pulmonary blood enters left atrium first week or two of life, babies actually
artery than in fetal circulation lose weight, up to 10 percent of their birth
weight, before starting a steady gain.
Foramen ovale Descending aorta
closes Looking and touching
Blood supply to Babies soon start to explore the world through
Liver lower body looking and touching. Young babies focus best
at about 8–14 in (20–35 cm) from an object
Inferior KEY and love to gaze at faces. The mouth and the
vena cava Oxygenated hands are important for touch sensations.
blood
Newborn circulation Deoxygenated
Oxygen-rich blood from the lungs passes blood
through the left side of the heart and on Mixed
to the body, while deoxygenated blood blood
from the body passes back to the right
side of the heart and on to the lungs for
the cycle to complete itself.

406

LIFE CYCLE

CHILDHOOD

Childhood is a time of continual physical change and
developmental progress on a scale that does not occur
again in life. Along with growth in height and weight
comes the acquisition of physical and mental skills,
social understanding, and growing emotional maturity.

GROWTH AND DEVELOPMENT First molar
(3rd)
The first two years of a child’s life are Central incisor Once a child has reached a particular Exploring the world
marked by extremely rapid physical (1st to erupt) UPPER milestone, practice and enthusiasm Every child has innate
growth, after which the rate slows until TEETH spur progress toward the next. curiosity about the world
puberty. The size and weight of all body Milk Lateral incisor and will learn from whatever
tissues and organs increase during teeth catches the attention.
childhood, with the exception of The first set (2nd)
lymphatic tissue, which shrinks. Both of teeth Second molar CHANGING PROPORTIONS
growth rate and final stature are largely usually starts (5th)
dependent on genetic inheritance, so to appear
that, to an extent, a child’s final height from about Canine
can be predicted from the height of 6 months. (4th)
the parents. However, growth and
development are also influenced by the LOWER
child’s environment, so health or illness, TEETH
nutrition, intellectual stimulation, and
emotional support all contribute to At birth, a baby’s head is relatively large, in spurts. The growth of the long bones
physical and mental outcome. representing one quarter to one third of the legs is largely responsible for the
of its total body length—compared with increase in height during childhood. The
Erupting teeth The cartilaginous joints in a baby’s skull just one eighth for an adult’s head. In first two years of life are the time of
Permanent adult teeth begin to erupt and facilitate rapid brain growth. The addition, a baby’s skull is quite large maximum growth. An average infant gains
baby teeth fall out at about 6 years of age. newborn’s brain is about a quarter of the compared with its face. The trunk of a around 10 in (25 cm) in height and triples
By the age of 13 a full set of adult teeth size it will reach at adulthood, but by its baby is about three-eighths of its total its birthweight in the first year. However,
(except for the wisdom teeth) has grown. third year it will have enlarged to 80 height—about the same as in an adult— after the age of two, growth usually settles
percent of its eventual size. While almost although its shoulders and hips are fairly down to a steady 21/2 in (6 cm) per year
all the brain’s neurons are present at birth, narrow and its limbs are relatively short. until puberty (see p.408), and eventually
their links are limited and interconnections Thus, as a child grows, its height and ceases at about 18–20 years.
will continue to develop until adulthood. weight gains are accompanied by distinct
Dental development during childhood is changes in body proportions. The trunk Body-head proportions
marked by the succession of the primary grows steadily throughout childhood but A newborn baby’s head is already almost
or “milk” teeth by permanent adult teeth, the head does not enlarge very much, adult-sized, whereas its limbs are relatively
which erupt through the gums below. although the face gets bigger relative short. As the child grows, increases in height
to the skull, while the limbs grow and weight are therefore accompanied by
proportionately very much longer, often changes in body proportions.

1

PROPORTION OF TOTAL BODY HEIGHT 3/4

Developing

bones 1/2
As a child grows,

the cartilage in the

skeleton gradually

turns to bone. In 1/4
adults, the wrist

consists of eight

bones, which

gradually develop

from cartilage 0

during childhood. BIRTH 26 12 18
AGE (YEARS)
2 YEARS 7 YEARS ADULT

407

CHILDHOOD

STAGES OF DEVELOPMENT

A child’s acquisition of skills and abilities vary enormously in the age at which they THE IMPORTANCE OF PLAY Manual dexterity
in different spheres is marked by certain achieve these stages or learn certain skills. Children develop the ability to grasp
achievements known as developmental Some children will miss out on certain Play is far from a trivial activity—it is crucial and manipulate objects very early on.
milestones. These may be seen as stages and go straight on to the next, and to the acquisition of physical, mental, and Gradually, they learn to perform
stepping stones to future development— a child who is “ahead” in one area may social skills. Unlike passive entertainment, increasingly complex movements.
children must be able to walk before they lag behind in others. New circumstances, play requires involvement, imagination, and
can run, and to understand and vocalize especially stress and changes at home resourcefulness. Pretend play stimulates
simple words before they can start to (such as a new baby or moving house) creativity and understanding, while playing
construct sentences. Once a child has may delay the achievement of milestones, with other children boosts communication
reached a particular milestone, practice but most children will adapt readily given and social skills. For a parent, playing with
and enthusiasm spur progress toward the time and support. Below is a guide to the children on their level is one of the best
next. Children are individuals and develop average ages at which children reach ways to give them emotional security and
at different rates, so even siblings may developmental milestones. cement the bond with them.

AGES (YEARS)
0 1 234 5

PHYSICAL ABILITIES • Lifts head and chest • Crawls up stairs • Runs easily
Many of a baby’s physical responses at birth • Brings hand to mouth • •Squats to pick up objects Can pedal and steer • Hops
are involuntary and largely reflex actions, such • •Grasps objects with hands Jumps with both feet • Can dress and undress unaided
as the suckling reflex. Gradually, but steadily, tricycle
a child will make the transition to more • Turns pages in a book • Climbs and descends stairs
purposeful and active motions, learning in • Controls bladder by day unaided
sequence to hold its head up, turn over, crawl, • Reaches for objects • Walks unaided
stand, and walk. Balance and coordination • Rolls over • Carries or pulls toys • Can catch and throw a
improve in parallel, and eventually • Supports own weight on feet • Starts to run
children learn the highly complex • Can kick a ball bounced ball
motor skills needed for
sophisticated activities such as • Draws basic shapes and figures
riding a bicycle or writing. • Uses scissors

• Crawls • Walks up and down stairs • Holds pencils with precision
• • •Walks holding furniture Can hold and use pencil Turns handles and jar lids • Can write some words
• •Bangs objects together Shows hand preference • Draws straight lines and circles • Feeds self using utensils
• •Eats finger foods unaided Gains control of bowels • Can build a tower to six blocks • Uses bathroom unaided

THINKING AND LANGUAGE SKILLS • • •Smiles at parent’s voice Starts to drink from cup Uses simple sentences • Understands future tense
Speech and language development are vital to a • Starts to imitate sounds • Can state name, age, and gender • Can state name and address
child’s ability to interact with their surroundings. • Uses pronouns (“I,” “you,” “we,” • Names four or more colors
An infant starts to understand basic words and • Begins to babble “he,” “they”) • Can color in shapes
commands long before being able to speak, and • Investigates with hands and mouth • Can count more than
verbal skills are readily learned by imitation. The • Reaches for out-of-reach objects • Understands spatial location
more parents and others involved in an infant’s • Understands “no,” “up,” and “down” (“in,” “on,” “under”) 10 objects
care talk to the child, the more vocal and verbal
the child is likely to become. • Begins to understand numbers • Able to distinguish reality
Along with growing understanding from fantasy
of the world, language helps the • •Understands basic grammar
child develop thinking, reasoning, • Recognizes own name • Points to named objects • Starts to count Understands concept of
and problem-solving skills. • Responds to simple • Sorts shapes and colors • •Starts to understand time money
• Says simple phrases
commands Aware of gender

• Uses first words • Follows simple instructions • Tells stories
• Imitates behavior • Engages in fantasy play • Follows three-part commands

SOCIAL AND EMOTIONAL • Makes eye contact • Imitates others’ behavior • Peak separation anxiety • Wants to please and to be
DEVELOPMENT • •Recognizes familiar people Enjoys company of other children • Shows affection for other children
Almost from birth, a baby recognizes its mother • •Cries when needing attention Demonstrates defiant behavior • Takes turns when playing like friends
and shows a marked preference for her over • Smiles at mother, then socially • Understands possession (“mine,” “yours”)
other people. Many children go through phases • Watches faces intently • Increasingly independent
of shyness with strangers but most are • Recognizes parents’ voices • Likes to demonstrate skills,
enthusiastic for interactions with
others. Soon they grow in such as singing, dancing, acting
independence and show a
capacity to control their behavior, • Shows empathy for others
understand social rules, cooperate,
and display empathy for others. • Responds to own name • Interested in new experiences
• Cooperates and negotiates
• Cries when parent leaves
• Shows preferences for people with other children

and objects • May imagine threats such

as “monsters”

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
AGE (MONTHS)

408

LIFE CYCLE

ADOLESCENCE AND
PUBERTY

Adolescence is the period of transition between childhood and
adulthood, during which puberty is marked by a great physical
transformation in both boys and girls and the onset of sexual maturity.

TRANSITION TO MATURITY

During adolescence, increasing physical maturity is family disharmony, falling school grades, or trouble with
authority. In addition to coping with the physical changes
accompanied by behavioral changes that mark the start of and hormone surges of puberty, teenagers are often
anxious about their body development, changing
growing up. As teenagers seek to develop their own sense appearance, and attractiveness to the opposite sex.

of identity, interactions with friends and peer groups gain

increased importance, and their social skills expand.

Adolescents are attracted to peer group interests, such as

music and fashions, and may become increasingly 180
170
distanced from their parents. They need to discover their 160
150
individuality and prove their independence in thought and HEIGHT (CENTIMETRES) 140
130
actions, so may start to take their values more from their 120
110
peers, making them vulnerable to peer pressure. Without a 100

strong sense of identity and self-confidence developed in 8 Girls and boys

childhood, they may be at risk from experimenting with KEY This may lead to body On average, girls reach puberty
Girls image problems, which two years before boys. The age
alcohol, drugs, smoking, and sexual relationships. Many Boys may spiral into eating difference in sexual maturity is
disorders. With all these paralleled by a similar gap in
teenagers have mixed Growth spurts 9 10 11 12 13 14 15 16 17 18 physical and mental development.
emotions as they try to Puberty marks a time of rapid AGE (YEARS)
establish their own values, growth in hormone-driven pressures, including
which may lead to rebellion spurts. Boys usually start later but
and negative effects such as grow more during peak periods. academia and future work, it is perhaps not surprising that

adolescents may come across as moody and volatile.

RAGING HORMONES Hypothalamus MIXED EMOTIONS

The hormonal surges that occur at puberty are responsible Gonadotropin- Surges in hormone levels have traditionally
releasing hormone been linked to fluctuations in mood and
for some of the most dramatic changes that ever occur emotions during puberty. However, sex
Pituitary gland hormones are now not thought to play the
in the human body. In both sexes, the trigger of puberty is major role. Instead, social and environmental
Luteinizing influences, coupled with physical changes
the release from the hypothalamus, a gland in the brain, hormone in the brain as it matures, are believed to
have a greater effect on the emotions.
of a hormone called gonadotropin-releasing hormone +
Follicle Appearance anxiety
(GnRH). This stimulates the nearby pituitary gland to stimulating The physical changes that take place during
hormone puberty provoke anxiety about appearance
release two more hormones called luteinizing hormone and attractiveness to other adolescents.

(LH) and follicle stimulating hormone (FSH). These in turn

travel through the bloodstream to trigger the production of

the sex hormones—primarily estrogens and progesterone Feedback Feedback

from the ovaries in girls and testosterone from the testes

in boys. These hormones are responsible for all the

developments underlying puberty in both sexes. Female

sex hormones stimulate the ovaries to start releasing eggs

and the body to prepare Feedback loops Testes Ovaries
for a possible pregnancy. Hormone production is regulated
Male sex hormones by feedback, when the amount
prompt the testes to start of a substance in the system
producing sperm. controls how much is produced.

The physical changes associated Sperm Testosterone Estrogen Egg
with puberty are initially triggered cells cell
by hormones in the brain.
Physical development

409

ADOLESCENCE AND PUBERTY

PHYSICAL DEVELOPMENT

The age of onset of the physical changes marking the start entering puberty boys are Ripening egg
of puberty is highly variable, but will often be around the
age that the same-sex parent made the transition. Most generally ¾ in (2 cm) shorter A girl is born with a full
girls enter puberty between age 8 and 13; most boys from
age 10 to 15. In both sexes, the sequence of physical than girls of the same age,at full complement of half a
changes that culminates in physical maturity lasts 2 to million eggs in her ovaries.
5 years. It will be complete in most girls by age 15 and adult height they are, on average, After puberty, several start

most boys by age 17. 5 in (13 cm) taller. to ripen each month, but
Both genders have a
In addition to boosting usually only one is released.
remarkable growth spurt
associated with puberty, at height, puberty marks the onset
its peak resulting in height
increases of up to 3½ in of sexual development, with growth and maturation of
(9 cm) in a year in boys,
and 3 in (8 cm) in girls (see the sex organs (testes and ovaries) to enable fertility
opposite). Although on
and secondary sexual characteristics. In both sexes

these include increased genital size, the appearance

of underarm and pubic hair, and skin changes that may Adam’s apple enlarges, the vocal chords stretch and the
voice deepens, muscle bulk increases, and additional
promote acne. In addition, girls undergo breast body and facial hair appears. Most boys will experience
spontaneous nocturnal ejaculations (also known as wet
development, their hips widen, and they lay down an dreams) during and after puberty.

extra layer of insulating body fat. Menstruation begins,

usually preceding the onset of ovulation. In boys, the

Sperm production Puberty marks the onset of sexual development,
Puberty triggers sperm with growth and maturation of the sex organs
production in the testes. It takes (testes and ovaries) to enable fertility.
72 days to produce a mature
sperm capable of movement.

Facial hair Adult height The growth spurt
The appearance of facial at puberty begins
hair is one of the last Facial hair starts two years earlier
changes to occur during as a light down, in girls than boys
puberty in boys, occurring becoming coarser
on average around age 15.

No facial hair Enlarged larynx results Armpit hair
Broadened in a deepening of
chest the voice Area around nipple
swells and becomes a
Lack of Armpit hair
muscle bulk mound with a small
Chest hair amount of breast
Pubic hair continues tissue underneath
Enlarged genitals growing until
age 30; some Pelvis and hips
men have little widen and waist
or no chest hair narrows due to fat

Narrow hips redistribution
influenced by
No pubic hair hormone changes

Muscle bulk increases Pubic hair
significantly

The male body The female body
Boys gain in height and As well as growing breasts,
weight, and develop a girl’s pelvis widens and
stronger and larger muscles. she develops an extra
The genitals enlarge, the layer of fat under the skin,
scrotum darkens, and hair resulting in a curvier figure
grows in the armpits, the with broader hips and a
pubic region, often on the narrow waist. Pubic and
trunk, and finally on the face. underarm hair develop.

BEFORE PUBERTY AFTER PUBERTY BEFORE PUBERTY AFTER PUBERTY

410

LIFE CYCLE

ADULTHOOD AND
OLD AGE

The inevitable progression from adulthood through
middle age to old age is accompanied by gradual
changes in all body systems. Although there are many
possible contributors to the aging process, scientists
still do not fully understand why we age as we do.

THE AGING PROCESS As their function is impaired, cells become Signs of aging 20-35
less capable of reproducing and replacing Perhaps the most visible outward signs of aging are
As we get older, all the cells in our bodies themselves. Gradual effects include wrinkling and discoloration of the skin, and graying Between these ages
undergo progressive changes that inevitably stiffening of connective tissues, leading to hair, which results from fading pigment. the body’s biological
affect the tissues and organs they comprise. loss of elasticity in the walls of the arteries, functioning and physical
During their lives, cells accumulate internal along with skin thinning, lowered performance reach
debris, enlarge, and become less efficient. immunity, and loss of organ function. their peak.
They are less able to take on board
essential nutrients and oxygen, or to get As people age they become less able Dying cell
rid of the waste products of metabolism. to cope with increased physical demands. The repair and renewal of tissues depends on a
For example, as heart muscle ages the process of programmed cell death called apoptosis.
Telomeres heart may be less able to increase its Normally, cells die in a controlled manner, to be
DNA strands at the end of each chromosome pumping capacity during exercise or replaced by new cells. With age, apoptosis is less
get shorter every time a cell divides, limiting stress. Similarly, lung and kidney capacities well regulated, contributing to disease.
the number of possible divisions and perhaps are gradually reduced. Also, the body
holding a clue to the mechanisms of aging. becomes less able to detoxify harmful
substances, meaning that older people are
more at risk from the side-effects of drugs.

Because immune function is reduced,
the body becomes more vulnerable to
illness and less able to cope with it.
Gradually, the body’s repair and renewal
functions wind down until a point is
reached at which the body may be unable
to recover from the onset of a disease.

METABOLISM AND HORMONES

Aging affects both the production of the slowly, so older people are more likely to MENOPAUSE
body’s hormones and the way in which develop diabetes. Reduced parathyroid
target organs respond to them. Output hormone levels affect levels of calcium The decline in estrogen production from a
and responses to thyroid hormones, in the body and this may contribute to woman’s ovaries eventually leads to cessation
which control the body’s metabolism, may bone thinning or osteoporosis. Reduced of ovulation and loss of fertility, along with
decline with age alongside a loss of secretion of aldosterone, a hormone from menopause, when periods stop. The transition
muscle tissue, which uses more energy the adrenal glands that regulates body may take several years, with the last period
than fat. This means that metabolic rate fluid and chemical balance, may impair on average at age 51 in developed countries.
decreases with age, so the body burns blood pressure regulation. Another After menopause, a woman is more
fewer of the calories in food. Unless this is hormone from the adrenals, called vulnerable to osteoporosis, cardiovascular
counteracted by exercise, to increase cortisol, is produced in response to stress, disease, and breast and endometrial cancers.
muscle mass, older people can develop and high levels seem to accelerate
a susceptibility to a rise in body fat levels. age-related changes. Estrogen levels Osteoporosis
From middle age, body cells become in women decrease markedly after the In the brittle bone disease osteoporosis, bones
less sensitive to the effects of insulin, menopause, whereas testosterone levels gradually lose density and strength, and
produced in the pancreas, with the result in men decline slowly, so male fertility can fractures of weakened bones, especially in the
that blood glucose levels tend to rise continue into old age. hip or spine, may occur (see p.427).

411

ADULTHOOD AND OLD AGE

SKIN MUSCULOSKELETAL AND ORGAN CHANGES 60

With age the outer layer of the skin gets Multiple changes occur in the compensate for less flexible joints and Male range
thinner, as does the underlying fat layer. musculoskeletal system with age, age-related arthritic changes. Even so, 50
Aging skin becomes less elastic and more including loss of bone density, joint older age is often accompanied by
fragile, with reduced sensitivity, so it not stiffening, and loss of muscle mass and stooped posture, muscle weakness, loss of
only sags but also is more easily damaged. tone. Older people become more liable agility, and slower movements, leading to
Blood vessels in the subcutaneous tissue to osteoporosis, in which calcium and changes in gait, made worse by impaired
become more fragile, so skin is more other important minerals are lost from the sensation and balance. With age the
susceptible to bruising. The sebaceous skeleton. This makes bones more porous heart’s pumping ability progressively
glands produce less oil, making the skin and brittle, reducing their strength and decreases and loss of elasticity in the
more prone to dryness and itching. increasing the risk of fractures. A good arteries may increase blood pressure,
intake of calcium and vitamin D, along putting further strain on a weakened heart.
Age spots with weight-bearing exercise, can Heart rhythm abnormalities become
Caused by strengthen bones and ameliorate some of more common as the heart’s electrical
exposure these changes. Exercise also mitigates loss conducting system is disrupted. Lung
to sun of muscle bulk with age and may partly capacity decreases as the elastic support
HEARING LOSS (DECIBELS) 40
MAXIMUM OXYGEN CONSUMPTION of the airways weakens,
(ML/KG/MIN) and, especially after age 30
65, this reduces the
amount of oxygen Female range
available to the tissues. 20

Loss of cartilage 10
in hip joint
Wrinkles 0 30 40 50 60
Give lined Osteoarthritis 20 AGE (YEARS)
appearance Wear and tear gradually erode
joint cartilage and may produce
Dermis osteoarthritis where joint Heart and lung performance
Contains less surfaces rub together. Pain and Both heart and lung function progressively decrease
collagen, so is stiffness become increasingly with age, so there is less reserve capacity to cope
less elastic common as people age. with additional demands.

Fatty layer Exercise mitigates loss of
Becomes muscle bulk and may
thinner partly compensate for less
with age flexible joints and age-
related arthritic changes.
Aging skin
Older skin has less subcutaneous fat and elastic
tissue and its glands produce less oil. Pigment
cells reduce in number but may get larger. The
skin appears paler but age spots may appear.

BRAIN, NERVES, AND SENSES

Like other body cells, those of the cognitive abilities. Vision and hearing also older people remain more vulnerable farsighted with age, and need reading
nervous system function less well as tend to become less acute, and the senses to accidents, memory loss, dietary glasses. Sharpness of vision and color
people get older. The brain and spinal of touch, taste, smell, balance, and impairment, and general reductions in perception may be dimmed and various
cord lose nerve cells, and those that proprioception may be impaired. While quality of life. Senility and dementia are eye problems, including cataracts, become
remain may accumulate waste products a healthy lifestyle with good nutrition, not normal or inevitable, although older more common. Reduced taste and smell
that can slow nerve impulses, reduce physical exercise, and mental stimulation people are more likely to develop can diminish enjoyment of eating and
reflexes and sensation, and blunt can ameliorate many of these changes, Alzheimer’s disease. Most people become contribute to nutritional deficiencies.

0 Decline in hearing Ventricle Subarachnoid space Ventricle Subarachnoid space

Loss in hearing with age

10 especially affects higher
frequencies, such as

women and children’s

20 voices, or ringing
telephones. Hearing is

more likely to be impaired

30 with age among people
who were exposed to loud

noises earlier in life.

40

50 3000 KEY Age 20 Brain of 27-year-old Brain of 87-year-old
FREQUENCY (HERTZ) 20000 Age 30 A brain scan in a young person shows little This scan shows considerable shrinkage and loss of
60 Age 50 atrophy—the shrinkage that represents loss of brain tissue, with expanding ventricles and enlarged
400 Age 70 brain cells with aging—and normal-sized subarachnoid spaces. There are also fewer cells in the
ventricles and subarachnoid spaces. hippocampus, the area where memory is processed.

412

LIFE CYCLE

END OF LIFE

Death is the cessation of all biological functions. It may result from
disease, trauma, or lack of vital nutrients. Unless one of these events
occurs, all people will eventually die of senescence—simple old age.

DEFINING DEATH viable organs for transplantation, may be 122
pronounced when it is judged that brain
Traditionally death has meant the cessation
of heartbeat and respiration, almost failure is permanent and irreversible, even
inevitably followed by irreversible bodily
deterioration and decomposition. Modern if heart and lung function is maintained The age of
medical technology has made it possible
to maintain vital body functions artificially, artificially. Similarly, brainstem death occurs
so that the boundary between life and when the brain is judged no longer capable Jeanne Calment,
death has become increasingly blurred. Death mask
We can now intervene in events that were of sustaining vital functions. Legal death is the longest- In past centuries, death masks were often made to record a
previously irreversible—such as cardio- simply when a doctor pronounces death, living human. person’s appearance. They were cast in wax or plaster immediately
respiratory arrest—and, as a result, death which may be contemporaneous with after death, before facial features could become distorted. This is
is now seen as a process, rather than an the death mask of Austrian writer Adalbert Stifter.
event, with varying definitions. Clinical pronouncement of brain death or some
death accords with the traditional definition they represent physiological changes in the
of the absence of vital signs of heartbeat time after clinical death. dying brain; others think that they are
and breathing—but from which individuals evidence of an afterlife, through reincarnation
may now be resuscitated. Brain death, a NEAR-DEATH EXPERIENCE or other spiritual phenomena.
criterion developed to enable removal of
Some individuals who have been Common visions
Intensive care pronounced clinically dead and then revived, Near-death experiences are often characterized
With advances in medical technology, failure of or who have undergone resuscitation after by a feeling of floating out of the body and
vital body functions can now be overridden by a cardiac arrest, report a set of strikingly moving through a tunnel toward bright light.
maintaining the patient artificially, especially similar perceptions known as near-death
by ventilators or “life support” machines. experiences. These include out-of-body
sensations, moving through a tunnel toward
a bright light, and encountering familiar figures
from their past. Usually these sensations are
experienced as positive. Some people believe

413

END OF LIFE

WORLDWIDE LOW-INCOME COUNTRIES HIGH-INCOME COUNTRIES CAUSES OF DEATH

Coronary artery disease 12.2 % Lower respiratory infections 11.2 % Coronary artery disease 16.3 % Worldwide, the leading causes of death
are linked with cardiovascular disease,
Stroke and other cerebrovascular diseases 9.7 % Coronary artery disease 9.4 % Stroke and other cerebrovascular diseases 9.3 % which is, to a large extent, preventable.
For example, scientists have shown that
Lower respiratory infections 7.1 % Diarrheal diseases 6.9 % Trachea, bronchus, lung cancers 5.9 % nine potentially modifiable lifestyle factors,
including smoking and obesity, account
Chronic obstructive pulmonary diseases 5.1 % HIV/AIDS 5.7 % Lower respiratory infections 3.8 % for more than 90 percent of the risk of
having a heart attack. Compared with
Diarrheal diseases 3.7 % Stroke and other cerebrovascular diseases 5.6 % Chronic obstructive pulmonary diseases 3.5 % high-income countries, low-income
countries have a much greater occurrence
HIV/AIDS 3.5 % Chronic obstructive pulmonary diseases 3.6 % Alzheimer’s and other dementias 3.4 % of death from infectious diseases. This is
Tuberculosis 2.5 % largely due to the effects of poverty,
Tuberculosis 3.5 % Colon and rectum cancers 3.3 % including inadequate nutrition, poor
hygiene, and lack of health provisions.
Trachea, bronchus, lung cancers 2.3 % Neonatal infections 3.4 % Diabetes mellitus 2.8 %
The most common causes
Traffic accidents 2.2 % Malaria 3.3 % Breast cancer 2.0 % These tables show the top 10 causes of death
Prematurity and low birth weight 2.0 % Prematurity and low birth weight 3.2 % Stomach cancer 1.8 % worldwide, and compare the leading causes of
death in developing and developed countries.

AFTER DEATH CHEATING DEATH

The human body undergoes many In future, new techniques to repair the Living longer
changes after death, which may be useful damage done by the aging process may hold The people of Okinawa, Japan, have the world’s
to establish a time of death if this is out the hope of extending the healthy highest life expectancy (82.6 years). Studies suggest
unknown. Usually, after an initial lag human lifespan. One promising line of that a combination of good diet, low stress, and
period of 30 minutes to 3 hours, the body research is the use of stem cells, high levels of physical activity is responsible.
progressively loses heat at an average rate which can reproduce indefinitely
of about 2.7°F (1.5°C) per hour until it Physical changes and develop into any new body
reaches the same temperature as its After death, the body slowly cools to the same cell. These might regenerate worn
surroundings. Muscles undergo chemical temperature as its environment and becomes out or diseased organs and so avert
changes that make them stiffen. This temporarily stiff, with the joints fixed in the or delay many leading causes of
process, called rigor mortis, begins with position at death. death. This might involve using a
the small facial muscles and works down
the body toward the larger muscles of the fixed. Finally, bacteria and enzymes start to person’s own stem cells or transplanting cells
arms and legs. Rigor mortis happens more decompose the tissues, and the body will from elsewhere. Potential applications include
quickly at higher temperatures and in start to smell after 24 to 36 hours. The skin repairing diseased heart muscle or nerve
thinner people. After around 8 to 12 hours, takes on a green-red hue, body orifices damage, reversing blindness and deafness,
the body has become stiff and fixed in the may leak, and the skin may split as gas and treating conditions such as cancer and
position of death. Thereafter the tissues forms in the putrefying flesh and body Alzheimer’s disease. Other approaches of
begin to decompose and the stiffness is cavities. The various procedures regenerative medicine include manipulating
lost during the following 48 hours. As undertaken by mortuaries are designed the genetic influences underlying aging
blood flow ceases, it pools in various parts to prevent this until after the funeral. or the major diseases of older age, targeting
of the body, creating a purple hue known body metabolism or hormones to delay
as lividity. Initially, the position of the age-related changes, and learning more about
discoloration is affected by moving the the factors that contribute to natural longevity.
body, but after 6 to 8 hours it becomes For example, studying the lifestyle of
centenarians may provide clues to how we
Bodies that are buried Stem cell research could all perhaps live a little bit longer.
in the ground after Adult stem cells become increasingly inefficient
death turn to skeletons with age. Scientists hope to find a way to replace
within about 10 years. or rejuvenate them, to repair age-related
damage to worn–out organs and tissues.

Post-mortem Although family history influences how long a
A body may undergo a medical person will live, many of the factors that affect
examination by a pathologist to discover lifespan are within people’s own control.
or further investigate the cause of death.

diseases
and
disorders

The body is a complex construction, vulnerable to disease and malfunction.
This section catalogs major diseases and disorders, starting with those that
are not specific to any single body system, such as infectious diseases and
cancer, and then moving on to look at each system of the body in turn.

414

DISEASES AND DISORDERS

416 Inherited disorders 438 Brain and spinal cord disorders 460 Allergies and autoimmune 474 Sexually transmitted diseases
418 Cancer 440 General nervous system disorders 476 Infertility
420 Infectious diseases 478 Disorders of pregnancy
422 Skin, hair, and nail disorders disorders 462 Upper digestive tract disorders
426 Bone and joint disorders 441 Nervous system infections 464 Lower digestive tract disorders and labor
430 Muscle, tendon, and 442 Mental health disorders 466 Liver, gallbladder, and 480 Endocrine disorders
444 Ear disorders
ligament disorders 446 Eye disorders pancreas disorders
432 Back, neck, and shoulder 448 Respiratory disorders 468 Kidney and urinary problems
452 Cardiovascular disorders 470 Female reproductive system
problems 456 Peripheral vascular disorders
434 Limb joint disorders 458 Blood disorders disorders
436 Cerebrovascular disorders 472 Male reproductive system

disorders

416

DISEASES AND DISORDERS

INHERITED DISORDERS

Defective genes and chromosome disorders are usually passed from parent to child. Chromosome
disorders are caused by a fault in the number or structure of the chromosomes. Gene disorders are
due to a fault on one or more of the genes that are carried on the chromosomes.

CHROMOSOME DISORDERS

Chromosomes are strands of coiled DNA, the genetic material arranged defects and disease. There may be errors on any of the chromosomes,
in a double helix that instructs our cells how to grow and behave. Humans such as breakages, missing pieces, extra pieces, or translocations (pieces
have 23 pairs of chromosomes—one in each pair from the father and one that are incorrectly swapped). These usually result from mistakes during
from the mother. Major chromosomal abnormalities can produce serious meiosis (cell division to form egg or sperm cells).

DOWN SYNDROME TURNER SYNDROME Around 98 percent of fetuses affected by AMNIOCENTESIS
Turner syndrome are not viable and are
A partial or complete extra copy of In this condition, girls are born with only miscarried. The condition affects about 1 in One of the tests that can be done to detect
chromosome 21 causes Down syndrome. one active X chromosome in each cell 2,500 live births. It is not fatal, although it can inherited abnormalities is amniocentesis.
The extra genetic material causes instead of two. It does not affect boys. cause medical problems. It cannot be inherited, At around 16–18 weeks of pregnancy, a
abnormalities in many systems. since affected individuals cannot reproduce. small amount of the amniotic fluid that
Girls with Turner syndrome share certain surrounds the baby is extracted using a
Down syndrome is the most common physical characteristics—they are of short 12 34 5 6 long needle guided by ultrasound. Cells
chromosomal abnormality in which the fetus stature, and they have an abnormal or absent from the baby, found in the amniotic
can survive. It is caused by a fault in the normal uterus and ovaries and are infertile. They may 7 8 9 10 11 12 fluid, can be examined for simple genetic
parental production of eggs and sperm (90 have abnormalities of other organs such as the information such as the presence of too
percent or more are eggs rather than sperm), heart, thyroid, and kidneys, but the condition 13 14 15 16 17 18 many or too few chromosomes.
giving rise to one that contains extra genetic varies among individuals. It is often only
material. This fault is more common in older detected when a girl does not reach puberty 19 20 21 22 BIRTH DEFECTS
women. In about 3 percent of cases, however, at the normal age. The underlying genetic
Down syndrome is due to one parent having defect probably results from a fault when x y Genetic and chromosomal abnormalities
a translocation, which means that a piece of the egg or sperm is made. In some cases, may be relatively minor, or incompatible
one chromosome 21 is attached to another mosaicism occurs (both X chromosomes are Turner syndrome chromosomes with successful development so that the
chromosome. This pattern of inheritance does present in some cells but not in others). This set of chromosomes from a female with fetus never reaches birth.
not increase with parental age. Turner syndrome shows only one X chromosome
KLINEFELTER SYNDROME rather than the usual two.
Down syndrome can be detected through
tests in early pregnancy and confirmed after Klinefelter syndrome only affects boys. physical and behavioral characteristics,
birth with a blood test. It causes learning It is caused by the inheritance of an extra including infertility with absence of sperm.
difficulties and affects physical appearance, X chromosome in each cell, in addition Individuals have low testosterone levels and are
causing characteristics such as floppy limbs, to the normal X and Y chromosome. often shy and lack muscularity, but in many
round face, and eyes that slant up at the outer cases the condition is not detected. Some men
corners. Children with the condition may with Klinefelter syndrome do produce sperm,
require long-term medical support, and life and assisted conception may be possible.
expectancy is shortened to about 50 years.

1 23 45 Individuals with Klinefelter syndrome are Birth defects are relatively uncommon and may
physically male due to the presence of the Y be caused by inherited factors or by behavior.
6 7 8 9 10 11 12 chromosome. About 1 in 500 males have an Many affected fetuses are lost early in pregnancy,
extra X chromosome. The XXY status results due to abnormalities in the chromosomes that
13 14 15 16 17 18 from an abnormality during sex cell division, are incompatible with further successful growth
leading to a sperm or egg with an extra X and development. Miscarriage is extremely
19 20 21 22 x chromosome. This leads to boys being born Clinodactyly of the little finger common, probably affecting at least 1 in 4
with two active X chromosomes in each cell This abnormal curving of the little finger toward fertilized eggs and possibly many more at a very
Chomosome set instead of the normal one. The presence of the the ring finger is often found in people with early stage. This may be due to interruptions
This set of chromosomes from a child with Down Y chromosome allows some of the genes on Klinefelter syndrome. However, it may also occur and problems in the complex series of genetic
syndrome shows the extra copy of chromsome 21 the extra X to be expressed. These are called without any genetic abnormality. maneuvers that take place when an egg is
that causes the condition. triploid genes and are thought to cause the fertilized. We may never know what proportion
syndrome. The condition causes a number of of egg-sperm interactions are faulty.

417

INHERITED DISORDERS

GENE DISORDERS inheritance. There are around 4,000 recognized inherited disorders
caused by defects of single genes. Recessive diseases occur when both
Chromosomes are made up of thousands of genes. Each gene provides parents pass on a faulty gene. Dominant diseases are expressed, or
the blue-print for making a particular protein that the body needs to partially expressed, if only one abnormal gene is inherited.
function. Abnormalities in these genes result in faulty instructions being
sent to dividing cells. Abnormal genes may be passed on through

HUNTINGTON’S DISEASE ALBINISM CYSTIC FIBROSIS

An abnormal gene on chromosome 4 This name is used for a group of genetic Recessive inheritance An inherited disorder, cystic fibrosis is
causes Huntington’s disease, a brain disorders causing a lack of the pigment If both parents carry the genes for albinism but do 1 in 25 white people. It produces thick
disorder that causes personality changes, that gives color to skin, eyes, and hair. not have the disorder, there is a 1 in 4 chance that secretions in the lungs and pancreas.
involuntary movement, and dementia. their child will inherit both affected genes.
Albinism is a recessive disorder, meaning that Cystic fibrosis (CF) is one of the most common
This is a dominant genetic disorder—if a person both parents need to have the affected genes give back a red reflection in bright light. There life-affecting genetic diseases in the West. The
inherits the abnormal gene from either parent, in order to pass on the condition. If both is no cure, but those with the condition are child of two carrier parents has a 25 percent
he or she will develop Huntington’s disease. parents are carriers, a child has a 25 percent advised to stay out of the sun. Problems with chance of having CF and a 50 percent chance
Children of an affected parent have a 50 chance of inheriting the condition and a 50 vision can be corrected to some degree. of being a carrier for CF. Testing for carrier status
percent chance of inheriting the disease, which percent chance of being a carrier. No prenatal is possible, as is testing of the fetus.
does not usually become apparent until the test is possible unless parents have previously affected only if she has two abnormal genes. A
fifth decade. Huntington’s is a degenerative had a child with albinism so that the particular male will be affected if he has one abnormal The gene responsible normally creates
brain disorder, which causes a progressive loss genetic abnormality can be identified. Usually gene from his mother; his father, who gave him the cystic fibrosis transmembrane regulator
of brain function, often resulting in abnormal the genes instructing the body to make pigment his Y chromosome, will not have bequeathed protein, important in the regulation of sweat,
movements and dementia. are abnormal. Individuals with albinism have him a matching gene. This is termed X-linked digestive juices, and mucus. CF is characterized
poor vision and little or no pigment in eyes, recessive inheritance: it is carried by women but by thick, dehydrated mucus in the lungs, which
Diagnosis is made through CT scan and skin, or hair, resulting in pale skin, fair hair expressed in men. It can also be expressed in a accumulates, attracting infection and causing
physical examination. Treatment may be given (which can be white), and eyes that are usually female who has two abnormal genes (from an lasting damage. The secretion of pancreatic
to relieve the symptoms. Those at risk can be blue or violet but with a thin iris that tends to affected father and a carrier mother). juices is also affected, impairing the absorption
tested, but many choose not to have the test, of nutrients from food. The severity of the
because the condition has no cure, and may COLOR BLINDNESS About 8 percent of males, but only 0.5 condition is variable, and modern medical
only affect them far into the future. percent of females, are color-blind. Most techniques have contributed enormously to
Color blindness is a difficulty in commonly, red and green are confused, but the health and life expectancy of those affected.
Enlarged distinguishing between colors. It is a there are many other variations, some of which
ventricles genetic condition more common in males. increase in severity through life, and others of Ribcage
which remain stable and cause few problems. Mucus in
Brain scan of Huntington’s disease Most color blindness is due to abnormal genes bronchi
This scan of sections through the brain shows on the X chromosome (where many genes that
enlarged lateral ventricles typical of Huntington’s are concerned with color vision lie) that lack a Cystic fibrosis lungs
disease, leading to loss of brain function. matching opposite number on the Y. It causes This colored chest X-ray shows the bronchi in a
a defect in the cones of the eye which are lung of a person with cystic fibrosis. They are filled
sensitive to different colors. Because the with mucus, causing recurrent chest infections.
abnormal gene is recessive, a female will be

ACHONDROPLASIA condition. People with achondroplasia have MULTIFACTORIAL Autistic child
one abnormal gene, but the matching gene in INHERITANCE Usually diagnosed in childhood, individuals
Defective bone growth caused by an the pair is normal. A combination of two with autism generally have unusual or
abnormal gene, achondroplasia is the abnormal genes is fatal before or soon after Most inherited diseases are multifactorial, problematic social and communication
most common cause of dwarfism, or birth. If both parents have achondroplasia which means that they result from a skills, sometimes with other unusual abilities.
extreme short stature. there is a 1 in 4 chance that the baby will not combination of genetic and environmental
survive and a 1 in 2 chance that the baby will factors. Genes may cause the condition
Achondroplasia affects around 1 in 25,000 also have dwarfism. There is also a 1 in 4 or increase the chances of it developing,
people. Affected people are typically not much chance that the baby will be of normal stature. and the condition may vary widely. Such
over 4 ft (131 cm) in height, due to a mutation However, most cases of achondroplasia are inheritance can be difficult to trace
in the gene that affects the growth of bones. due to new mutations of genes, with neither through families. Autism is one example of
Altered body proportions also result from the parent being affected. It is not possible to carry multifactorial inheritance, and it may be
the gene without showing its effects. There is caused by a number of genes.
no cure, and treatment is rarely needed.

418

DISEASES AND DISORDERS

CANCER

Cancer is most often a growth or lump caused by the abnormal multiplication of cells that spread
beyond their natural space. It is not a single disease but a large group of disorders with different
symptoms, and may be caused by faulty genes, aging, or cancer-causing agents such as cigarettes.

BENIGN AND MALIGNANT In a dividing cancer cell, Normal cells remain Hard deposits Ulcerated areas may
TUMORS rapidly dividing abnormal between the of calcium may develop where the tumor
cancerous ones build up in tumors erodes the epilethial layer
cells force their way
between normal ones Tumors often form in
the epithelial layer,
A tumor is a growth or lump. Malignant which covers and lines
tumors can invade normal tissue and tissues and organs
spread to other parts of the body. Benign
tumors do not spread. Bleeding is caused
by cancerous cells
A tumor is a mass of cells that divide Cancerous cells are often oversized Cancerous cells form disrupting and
abnormally quickly and fail to carry out their and disorganized, with big nuclei tendril-like outgrowths that breaching tiny
usual function. These growths can be benign infiltrate surrounding tissues blood vessels
(noncancerous) or malignant (cancerous), Malignant tumor growth
depending on the behavior of the cells. Malignant tumors tend to produce substances Lymphatic vessels
that break down other tissues, allowing them provide a route for
Generally speaking, malignant tumors have to infiltrate and become difficult to separate cancer cells to spread
the greatest potential to cause harm—but not surgically, and to break off and spread via blood
all do so. Rapid growth and fast cell division, and lymph to seed in distant parts of the body. SCREENING FOR CANCER
more structurally abnormal cells, and a pattern
of spread all suggest greater malignancy. Benign Normal cells Some cancers can be detected before
growths are also caused by changed cells that they cause symptoms; screening for these
multiply abnormally and do not carry out their A fibrous capsule is an The body of the tumor cancers looks for changes in cells before
proper functions. Unlike malignant cancers, outer shell that envelops may enlarge slowly or they become cancerous (such as in colon,
they grow slowly and do not spread. and contains the tumor rapidly, depending on cervical, and prostate cancers). This allows
genetic changes in detection of conditions that may progress
Treatment may be given for benign tumors Benign tumor cells are the cells to cancer but have not yet done so,
if they bleed or press on important structures, regular in shape and size enabling intervention and prevention.
but generally benign tumors are less likely to Other cancers may be detected at an early
progress and cause harm. It is important to stage, which may be asymptomatic (have
detect whether a tumor is benign or malignant no symptoms). This is commonly done for
because cancerous cells can spread through the breast cancer. If caught early, curative
body. Malignancy is usually tested by taking a treatment is more likely to be possible.
sample of the affected tissue and checking its
behavior microscopically. Some cancers
produce specific chemicals, and measuring the
levels of these substances can also help in
diagnosing the type of cancer.

Cancer cells dividing Fibrous capsule A system of blood vessels Mammogram
This magnified image shows a cancerous cell forms a boundary that allows oxygen and nutrients Testing for breast cancer is done using a
dividing to form two cells containing damaged prevents tumor cells from mammogram. This is a special X-ray
genetic material. Untreated cancer cells multiply to reach the tumor technique that shows tissue in the breast and
uncontrollably and spread through the body. spreading allows cancer to be detected at an early stage.

Benign tumor structure
Benign tumors remain easy to separate
from surrounding structures. They do not
break down other tissues, or spread, but
remain surrounded by a capsule. Usually
they cause problems only if they grow
too big or press on surrounding organs.

419
CANCER

HOW CANCER STARTS trigger is usually damage to the DNA of genes growth, and chemotherapy, which damages TREATMENT OF CANCERS
called oncogenes, which program cell cellular DNA, can actually cause cancer.
Cancer is often triggered by carcinogens behavior. If mutated or damaged, oncogenes Viruses including hepatitis C can also damage Cancer may be treated with surgery to
(cancer-causing agents) such as tobacco. may prevent the normal processes of natural DNA. Successful repair requires a functioning remove a tumor, with radiation therapy,
Faulty genes may increase the risk of cell death (apoptosis), and instead encourage immune system, so cancer risk is increased or with anticancer drugs known as
developing the disease. cells to keep dividing. when a person has a condition that leads to chemotherapy, which kill cancer cells.
weakened immunity (such as AIDS). Cancer
Cellular damage occurs all the time, but the Various substances can damage DNA is also more likely to result if the damage is Some cancers—particularly early cancers and
body’s DNA usually repairs itself. Several things and are carcinogenic (cancer-causing). They repeated, or severe, and sustained, or if the benign tumors—are cured by surgery to remove
have to occur for a cancer to begin. The initial include radiation such as sunlight, toxic person has inherited defective oncogenes. In the tumor. Surgery is also used to reduce the
chemicals such as alcohol, and many of the these cases the damage becomes permanent, size of tumors prior to other treatment, or to
Carcinogen byproducts of tobacco. Sex hormones may and key cell functions are irreparably affected. prevent them from damaging the surrounding
provoke cancers by overstimulating cell tissue. Radiation therapy destroys cancer cells
Normal gene Permanently using high-intensity radiation. It can cure the
Permanently damaged disease or slow or prevent its growth, and it
Newly damaged oncogene can be accurately focused on surgically
damaged oncogene inaccessible tumors. Side effects include
oncogene Repaired fatigue, loss of appetite, nausea and vomiting,
Nucleus Newly oncogene and painful skin at the site of the treatment. It
damaged may be used along with other treatments.
Chromosome oncogene 3 Cell becomes cancerous
If the oncogene is permanently damaged, Chemotherapy includes different chemical
1 Damage from carcinogens Repaired then abnormal cell growth can begin. The agents that target damaged or mutated
Carcinogens damage the DNA of oncogenes, oncogene malignancy depends on the nature of the affected oncogenes (genes that have mutated and cause
which manage the normal restrictions on cell cells and the manner in which they grow. tumors), growth factors, and the division of
growth. Toxins, radiation, and viruses can all 2 Permanent damage cancer cells. Some agents work against all
damage DNA, which is under constant attack. While DNA can repair itself, if damage is dividing cells, and side effects such as hair
severe or sustained or if the repair system fails, loss or nausea are caused by the normally
HOW CANCER SPREADS oncogenes may be permanently damaged and rapid division of hair follicles and gut cells.
their cancer-preventing function switched off. Others pick on specific characteristics of
Cancer spreads by local growth, and when certain cancers and target all cells with that
cells break off from the tumor and are SPREAD BY LYMPH Lymph vessel Lymph node Cancerous cell Immune characteristic. The treatment may cure the
carried via the blood or lymphatic system Cancerous cell cell disease or relieve its symptoms, and can be
to other parts of the body. given orally or into the bloodstream or spinal
1 Lymph vessel breached 2 Tumor in lymph node fluid. The success of the treatment depends on
Local cancer growth occurs through the As the primary tumor grows, its cells invade Cancerous cells entering a local lymph node the age and general health of the person being
growth and multiplication of cancer cells in adjacent tissues. The lymphatic vessels form a can start to divide and grow into a secondary treated and the type of cancer.
their original site. If the cells look and behave suitable transport system for abnormal cells to tumor (metastasis). Immune cells here may halt
normally and spread neatly, pushing at local move around the body. the spread of the disease temporarily. Radiotherapy treatment
tissues rather than growing into them, the Radiation is used to destroy cancer cells. During
cancer is behaving in a benign way—even SPREAD BY BLOOD Cancerous cell Normal tissue Secondary tumor the treatment, high-intensity radiation is carefully
though it may grow rapidly. Malignant cancer Blood vessel focused on the cancerous area to destroy it or
cells produce substances that allow them to 2 Secondary tumor formed slow its growth.
break into other structures, growing through 1 Blood vessel wall ruptured Cancerous cells may be bigger than red blood
other tissues (local invasion) and potentially The rupture of a blood vessel wall as a tumor cells and can become lodged in narrow vessels.
breaching the walls of blood vessels, lymphatic expands may cause bleeding and allow tumor cells As the cells divide, they push into surrounding
vessels, and important structures. to enter into the blood system. In this way they can tissues, establishing a secondary tumor.
be transported to virtually anywhere in the body.
The main routes of spread are through the
blood and lymph systems, the body’s main
ways of distributing nutrients and collecting
waste. Once the walls of blood or lymph
vessels are breached, cancer cells can enter
those vessels and be transported to other sites
in the body—often the liver, brain, lungs, or
bones. When they lodge in these distant areas,
more aggressive cancers can become
established and start growing independently
of the original tumor. This is called metastasis,
and the distant growths are called metastases.
Particular cancers tend to spread to characteristic
places; for example, bowel cancer typically
spreads to the liver, because the blood vessels
of the bowel travel from there to the liver for
processing products of digestion.

420

DISEASES AND DISORDERS

INFECTIOUS DISEASES

Infection is the invasion of the body by pathogens (harmful microorganisms) that
multiply in the body tissues. Organisms that can produce infectious disease include
viruses, bacteria, fungi, protozoa, parasites, and aberrant proteins called prions.

ROUTES OF INFECTION the mucous membranes of the eyes, nose, VIRAL INFECTIONS
ears, digestive tract, lungs, and genitals, by
The body is constantly exposed to inhalation, absorption, or ingestion. From Viral pathogens range from the relatively
infection, but disease only occurs when there they may spread in the bloodstream harmless, such as those causing warts and
an organism overwhelms the immune (as with HIV), along nerves (like rabies), or the common cold, to the life-threatening,
system’s attempts to overcome it. by invading body tissues (as in invasive as in HIV (which causes AIDS).
gastroenteritis). Most pathogens, apart from
Infectious organisms can enter the body via prions, are living organisms, and when they Viruses are the smallest type of infectious HIV virus budding from cell
any breach of its natural defenses: through the enter the body the immune system typically organisms, made of genetic material inside a Once the virus has used the body cell’s DNA and
skin, by puncture or other injury or through mounts a response to fight them off. This coating of protein. They cannot multiply alone, reproductive mechanisms to replicate itself, the
response produces the symptoms of illness, but invade body cells and use their replication daughter organisms bud out from the cell and are
such as fever, inflammation, and increased mechanisms to multiply. The new particles each free to infect further cells.
production of mucus. The severity of the then burst out of the cell and destroy it, or bud
disorder depends on the strength and numbers through the surface, and travel to infect further above the optimum level for replication.
of the invading organism and the immune cells. Infections are usually systemic, involving Inflammation occurs when the immune system
response of the host. Some infections last only many parts of the body at one time. directs disease-fighting white blood cells and
a short time before either defeat by the host’s chemicals to the affected area. Viruses can
defenses or the death of the host. Others Many of the symptoms they cause, such affect any organ or body system. They
become chronic. as swollen glands and nasal congestion, are commonly cause rashes, but do not often
in part due to the activation of the immune produce pain. An exception are the Herpes
Airborne infections system to fight the invasion. The immune zoster virus 3 , which causes chickenpox and
Many viruses and bacteria spread by airborne response commonly begins with a fever, shingles, and the Herpes simplex viruses 1 and 2,
droplets, expelled from the nose or mouth when which is in essence an attempt to slow viral which cause cold sores and genital herpes.
people cough or sneeze, then entering a new replication by increasing the body temperature
host, via the mucous membranes.

BACTERIAL INFECTIONS poisoning). Symptoms vary according to the ANTIBIOTIC RESISTANCE Plasmid transfer
site of infection, and include pain, fever, sore
Bacteria can cause illness by multiplying throat, vomiting or diarrhea (as the body tries All organisms adapt to cope with changes in DONOR Pilus RECIPIENT
so fast that the immune system cannot to expel the infection), inflammation, and pus their environment. Since humans started
control them, or by releasing toxins that (a buildup of white blood cells and dead using antibiotic drugs, bacteria have evolved 2 Spread of plasmids
damage body tissues. material). Bacterial infection can follow viral many mechanisms to withstand them, such Plasmid transfer takes place during a
infection: tissues inflamed by a virus allow as plasmids. Once a method of withstanding process known as conjugation. The plasmid
Bacteria are single-celled organisms, much bacteria to multiply. Many infections can now a drug has been randomly generated by copy is passed from the donor through a tube
larger than viruses and capable of reproducing be treated by antibiotics, which kill bacteria, one of millions of dividing bacteria, it is called a pilus to the recipient bacterium.
independently. They exist everywhere in the but some bacteria have evolved to become coded onto a piece of genetic material, the
environment. The human body contains many resistant to these drugs (see right). plasmid, and transferred between bacteria, Drug-inactivating
types, largely on the skin and in the gut. Most rendering the antibiotic useless. enzymes
coexist harmlessly with us, and many are Streptococcus bacteria
beneficial. However, if the immune system is The enhanced electron micrograph shows Drug-inactivating Duplicated
weakened by an injury such as a burn, or by Streptococcus pyogenes, the bacteria that can cause enzyme plasmid
illness, some can become infective; for scarlet fever. Sufferers have a sore, pus-coated
example, Staphylococcus aureus lives on the throat, red tongue, fever, and a scarlet rash. 1 Activity of plasmid 3 Drug-resistant strains
skin, but in people with reduced immunity can Plasmids may cause the bacterium to make Whole populations of bacteria become
cause boils or even invade the bloodstream. enzymes against antibiotic drugs, or to alter its resistant to a range of antibiotics; some types
surface receptor sites, to which antibiotics can cause serious illnesses, such as methicillin-
Other disorders are caused by bacterial bind. Then the plasmids duplicate themselves. resistant Staphylococcus aureus (MRSA).
pathogens that invade the body and spread via
the bloodstream, body fluids, or tissues. They
may infect one area, as in meningitis (affecting
the membranes of the brain and spinal cord),
or the whole body, as in septicemia (blood

421

INFECTIOUS DISEASES

FUNGAL INFECTIONS Candida organisms membranes such as those lining the mouth or Athlete’s foot
Candida albicans is a yeast infection that lives the vagina; for example, Candida albicans can Also called tinea pedis, athlete’s foot is a fungal
Infections caused by fungi or yeasts naturally in the bowel of many healthy people but cause oral thrush, with a thick white coating, skin infection on the feet, usually between the
rarely result in harm unless the immune can be an opportunistic pathogen of other parts itching, and soreness, or vaginal yeast, with a toes. The tinea fungus favors warm, moist spaces;
system is weakened, in which case of the body in people with weakened immunity. vaginal discharge. Infective fungi can also enter it can also occur on the scalp or in the groin.
overwhelming infection is possible. the body from soil or decaying material.

Yeasts and fungi are simple organisms that Some may enter via broken skin as in
grow as colonies of round single cells (yeasts) sporotrichosis which causes a skin infection;
or in long threads (filamentous fungi). Many others may be breathed into the lungs and
live on moist areas of the skin, where they spread through the body, as in aspergillosis.
cause only minor symptoms such as flaky skin Fungal infections do little harm to healthy
or rashes. They can also inhabit mucous people, and most can be cured with antifungal
drugs. People with a weakened immune system,
such as those with AIDS, may develop serious
illness, even from normally harmless fungi.

PROTOZOAL INFECTIONS WORM INFESTATIONS different times. Worms enter the body through
ingestion, reproduce in the digestive tract, and
Particularly common in tropical regions Worms interfere with the body’s supply emerge from the anus to lay eggs, which can
or in areas with poor sanitation, protozoa of nutrients, hijacking it for their own then be transferred to a new host. Millions of
enter the body via vectors (carriers) such benefit. Most are passed on through people are affected worldwide—in developing
as mosquitoes, or from food or water. poorly cooked food, water, and feces. countries, helminthic infection is widespread
and a common cause of anemia. In the West,
pinworms is the most common infestation.

Protozoa are single-celled organisms. Many Worms, also called helminths, live inside and human diseases began as zoonoses, including Tapeworm
live in water or other fluids, and they tend to feed off living hosts, usually attaching via a influenza, measles, smallpox, and HIV. The Tapeworms live in the gut of a host, classically
flourish in warmer climates. The best known mouth structure within the gut to drink the common cold probably came from birds, and causing weight loss despite increased food intake.
protozoal infection is malaria, caused by blood. They are sequential hermaphrodites; tuberculosis may also have begun in animals. In Humans become infested by eating traces of
Plasmodium parasites, which kills more than a in other words, they may be male or female at the early stages of the encounter, the organisms contaminated meat or ingesting traces of feces.
million people each year. The parasites spend have not yet adapted well to
some stages of their life cycle in mosquitoes, ZOONOSES their new host, which is likewise illnesses, the human is a dead-end host, often
which transmit the infection to humans via not adapted to them with an infected accidentally, as in anthrax, rabies, and
bites. They enter the bloodstream and multiply Zoonoses are diseases caught from other immune response. Catastrophic HIV. These diseases made the “species leap”
in the liver, then penetrate and destroy red animal species. Many are extremely infection then results as the recently in evolutionary terms. Over time, a
blood cells. This causes a malarial attack, with serious, and some cause widespread host dies quickly. pathogen adapts to its new host, which in turn
high fever, chills, headache, and confusion. illness in human populations.
To survive and reproduce acquires immunity,
There is no vaccine, but infection spread As pathogens evolve, they occasionally mutate successfully, an infective so zoonoses become
can be reduced by mosquito control measures, (change) and cross the species barrier. This organism needs to stay alive in milder over time.
nets, and repellents. Other protozoal infections, is true of bacteria (for example, plague), a living host. In severe zoonotic
such as amebiasis and giardiasis, are spread viruses (such as rabies), protozoans (such as Lyme disease
via contaminated food and water, and cause toxoplasma), abnormal proteins (for example, Spread by ticks, the
digestive symptoms such as abdominal pain Creutzfeldt-Jakob disease), or worms. Many bacterium causes a
and diarrhea. Toxoplasmosis is a worldwide rash and flulike
protozoal infection and can be contracted via symptoms and, if
contact with cat feces or undercooked meat. untreated, heart and
joint problems.
Blood cell Plasmodium vivax protozoan

Malaria protozoa IMMUNIZATION many common bacterial and viral diseases,
The Plasmodium parasites spend part of their life including tetanus, diphtheria, polio, hepatitis B,
cycle within human red blood cells. The parasites The body normally becomes immune to and seasonal flu. It has effectively eradicated
multiply inside the cells, causing them to rupture, infections only after it has overcome them, smallpox worldwide. Other infectious
thus releasing the parasites to invade new cells. but immunization allows immunity to organisms, such as HIV, have proved to be
develop without exposure to the disease. more of a challenge because they change their
Most immunization is done by vaccination; form rapidly and frequently.
the injection of either an “attenuated” form
of the disease-causing organism (which Measles vaccination
is alive but not dangerous) or a dead Measles used to be a common infectious disease
vaccine (made from the protein coat of an of childhood. However, immunization of whole
organism), to provoke the immune system populations of children has enabled the disease
into attacking the organism. Alternatively, to be relatively well controlled in the West.
antibodies (immune system proteins) from
other humans or from animals may be
given. Immunization is available against

422

DISEASES AND DISORDERS

SKIN, HAIR, AND NAIL DISORDERS

The skin is frequently exposed to irritants and microorganisms and can become inflamed BIRTHMARKS
and infected. Skin cancers are usually caused by excessive exposure to sunlight. Nail and
hair disorders may be due to localized disease or general health problems. Birthmarks are colored marks on the skin
that commonly develop before or soon
ATOPIC ECZEMA as house dust mites, pollen, and pet skin and after birth. These include café au lait spots
saliva; and stress and fatigue. Typically, the (permanent oval, light brown patches) and
Eczema is a common long-term condition condition occurs in the creases of the skin port wine stains (permanent red or purple
that causes itching, redness, dryness, and around elbows, knees, ankles, wrists, and neck. patches). A strawberry nevus (pictured
cracking of the skin, usually in children below) is caused by abnormal distribution
prone to allergies. A patch of eczema begins as itchy red skin. of blood vessels and usually diminishes by
This progresses to dry scaling, and the skin may 6 months of age. Stork bites (pink patches)
eventually thicken further, with accentuated and Mongolian blue spots (large blue
skin lines and severe dryness, cracking, and bruises) usually fade in childhood.
fissuring. Eczema has no cure, and it may
Around one fifth of children develop eczema, Eczema on the arm cause considerable emotional distress.
but most grow out of it by adulthood. Very The affected skin is reddened and thickened, with Treatment includes avoiding the triggers, using
rarely it begins in adulthood. The condition prominent skin creases and markings, crusting, anti-itch medications, and using topical
runs in families and often occurs with hay fever and fissuring. It is very itchy and can be painful. emollients to reduce dryness of the skin.
and asthma. It affects both sexes equally. Topical corticosteroids or immunosuppressives
Eczema may come and go, with flare-ups are used either during flare-ups or more
triggered by ingesting allergens such as dairy regularly, depending on the severity of the
products or gluten; contact with allergens such condition. Infected eczema requires antibiotics.

CONTACT DERMATITIS IMPETIGO needed to treat the infection and prevent it
spreading to others. It is highly contagious
Contact dermatitis is an inflammation of A highly contagious superficial bacterial through direct contact with lesions or sharing
the skin due to an allergic reaction or infection of the skin, commonly on the linen and towels. Complications are rare but
caused by direct irritation to the skin. face, impetigo rarely causes complications. include cellulitis and septicemia.

Irritant contact dermatitis is more common Two types of impetigo are recognized, Impetigo infection
than allergic contact dermatitis and may be depending on whether large blisters (bullae) An infected fluid-filled vesicle or pustule ruptures
due to a wide variety of chemical or physical form. Nonbullous impetigo is most common. and then develops a golden-yellow crust.
irritants. Common chemical causes include It typically starts as a painless red fluid-filled Touching affected areas may transfer the infection
solvents, abrasives, acids and alkalis, and soaps. blister that rapidly bursts, causing weeping and to other areas of the body and other people.
Physical causes include prolonged friction from crusting, typically around the mouth and nose.
clothing and certain plants. Allergic contact Skin affected by dermatitis In bullous impetigo, blisters are larger and may
dermatitis is most commonly caused by metals Work-related contact dermatitis is common in take days to burst and crust; they are most
(such as nickel jewelry), adhesives, cosmetics, certain occupations such as hairdressing, where common on the arms, trunk, or legs. Impetigo
and rubber. Symptoms include a burning, the hands are repeatedly exposed to the mild heals in a few days without scarring. It is
itchy, or painful red rash, blisters, and hives. If chemicals in shampoos. common in children, people living in confined
due to allergy, dermatitis may take up to 3 days environments, or contact sport players. Topical
to develop; with an irritant, the inflammation is often immediate. Affected skin may become (applied externally) or oral antibiotics are
dry, thickened, and cracked over time.
Treatment includes avoiding trigger factors and
using emollients and topical corticosteroids.

PSORIASIS skin injury, drugs, and physical or emotional condition is diagnosed on its appearance.
stress. Around 80 percent of those with the Psoriasis responds well to natural sunlight
Psoriasis is a long-term skin disorder in disorder have plaque psoriasis, where red, flaky or phototherapy (UV light) but is usually
which the skin cells reproduce too patches (plaques) covered in silver scales a long-term condition. Topical (external)
rapidly, causing itchy, flaky patches. appear usually on the elbows, knees, and scalp, treatments include emollients, coal tar-based
which are itchy and sore. In flexural psoriasis, preparations, corticosteroids, dithranol, and
Psoriasis affects around 1 in 50 people. Men less scaly patches occur in skin folds such as vitamin D and A analogues.
and women are affected equally, and it runs in the groin and armpit. In guttate psoriasis,
families. It begins between the ages of 10 and smaller scaly red patches occur all over the Plaque psoriasis
45 and can be triggered by a throat infection, body in a young person, following a throat Patches (plaques) of the skin are thickened, red,
infection. It usually clears up completely. flaky, and covered in silvery-white scales, and have
Psoriasis may affect only the scalp. The a sharp border. They usually itch and may burn.

423

SKIN, HAIR, AND NAIL DISORDERS

RINGWORM in the webs between toes. Onychomycosis URTICARIA Red swelling caused by urticaria
(fungal infection of the nails) causes the nails The red, itchy, raised areas of skin due to urticaria
“Ringworm” is an umbrella term for a to become thick, yellow, friable, and deformed. Itchy red raised bumps on the skin, can vary in shape and size. Typically, they are
variety of common fungal infections of Fungal infections are diagnosed by their urticaria (“hives”) is commonly caused by round but can form into rings or large patches.
the nails, scalp, and skin. appearance and microscopic analysis of skin an allergic reaction and lasts a few hours.
scrapings or nail cuttings. Treatment is with In chronic (long-lasting) urticaria, the hives last
Ringworm (tinea) infections are classified by the oral or topical antifungals, depending on the Urticaria is caused by the release of histamine more than 6 weeks (sometimes years), usually
site of infection; usually warm, moist areas that site and severity of the infection. and other inflammatory substances from skin no cause can be found, and it can be difficult
allow fungi to thrive. In tinea corporis, an cells. These substances cause small blood to treat. Investigations include allergy testing
enlarging, red, itchy, slightly raised, ring-shaped Ring-shaped rash of tinea corporis vessels in the lower layer of the skin to leak and searching for triggers. Treatment involves
skin rash develops on exposed body areas (for A raised red ring with healing within the center fluid. About 1 in 4 people develop urticaria avoiding the triggers and taking oral
example, face and limbs). It is contagious by is characteristic of ringworm. Scales, crusts, and in their life, usually as children or young adults, antihistamines during attacks or to prevent
direct contact or via contaminated items such papules may develop especially on the advancing and it is more common in women. Acute them. Oral corticosteroids may be used to
as clothing, animals, carpets, and bathing edge. Ringworm is most common in children. urticaria lasts less than 6 weeks; most cases treat chronic urticaria.
surfaces. In tinea capitis, which mainly affects last only a few hours.
children, scaly patches appear on the scalp
and the local hairs break off. Allergic urticaria is commonly due to food
or drug allergies or direct skin contact with
In tinea cruris (“jock itch”), an itchy, red, raised substances. Nonallergic causes of urticaria
rash develops in the skin folds of the groin and include certain foods (such as rotten fish),
enlarges with a redder, more raised advancing stress, and an acute viral illnesses. In the rarer
edge. In tinea pedis (athlete’s foot), scaling, physical urticarias, pressure, exercise, heat and
flaking, and itching of the feet occurs, especially cold, vibration, and sunlight may cause hives.

ACNE VULGARIS leaving “ice-pick” scars that look like holes appearance. Treatment depends on the and azelaic acid. Visible improvement may
punched into the skin, or keloid scars that are severity of the condition, but includes take 2–3 months. Severe acne may require
Blockage and inflammation of the red and lumpy. It is important not to squeeze combinations of oral antibiotics for many 4–6-months of an oral retinoid, which is a
sebaceous glands leads to spots on the or pick lesions, to prevent scarring. Acne is months with topical treatments such as powerful drug used by specialists. Acne scarring
face, upper chest, and back. Acne affects diagnosed by its typical benzoyl peroxide, retinoids, topical antibiotics, may require dermabrasion or laser therapy.
nearly all teenagers.
Hair

Acne may last for many years with repeated Free flow Dark Plug
flare-ups but typically disappears by the age of sebum pigmented Bacteria
of 25. Acne is more common in boys and may plug build up
run in families. Adult acne occurs mainly in Sebum
women and may worsen a few days before Sebaceous Sebum Sebum
menstrual periods or during pregnancy. Drugs gland Sebaceous
such as corticosteroids or phenytoin may Sebaceous gland
cause acne. The condition is neither infectious Follicle gland Follicle
nor due to poor hygiene but does cause
much psychological distress. Follicle

The skin itself appears greasy. The lesions Normal hair follicle Blackhead Infected follicle
that develop include open comedones The pilosebaceous unit consists of a hair follicle, In acne, excessive amounts of sebum are Harmless bacteria that live on the skin that
(blackheads), closed comedones (whiteheads), a sebaceous gland, and, a sebaceous duct. The produced and a large plug of sebum and dead contaminate the plugged follicle, causing
papules (red bumps), and pustules (pus-filled gland produces oil called sebum that flows out skin cells blocks the follicle, forming a blackhead inflammation and infection, which leads to
bumps). Severe cases may include nodules of the skin pore to lubricate the skin and hair. (comedone), which is dark due to pigmentation. papules, infected pustules, nodules, and cysts.
(painful, deep, large, hard lumps) and cysts
(painful, large, pus-filled lumps that look like
boils). These may scar when they rupture,

ROSACEA chest and typically lasts a few minutes. Rosacea vessels (telangiectasia) can become prominent
has a variety of triggers including caffeine, on the skin. The skin may thicken and, rarely,
Rosacea is a long-term skin condition that alcohol, sunlight, wind, spicy foods, and stress. the nose can become bulbous and disfigured
primarily affects the face of fair-skinned Persistent facial redness on the cheeks, nose, (a condition known as rhinophyma).
people, causing flushing and redness. forehead, and chin may develop. Spots and
pustules may appear, and small red blood Rosacea is diagnosed by its characteristic
Rosacea is twice as common in females as appearance. Treatment includes avoiding
males and starts after the age of 30. It causes Redness on the face caused by rosacea triggers and, if severe, using topical or oral
facial flushing that may spread to the neck and The face is red and liable to flush easily. There are antibiotics. Camouflage creams may be used
red bumps (papules) and some pus-filled spots to cover the rash. Telangectasia can be treated
(pustules), which can be mistaken for acne vulgaris. with laser therapy. Cosmetic treatment for
rhinophyma may require surgery.

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DISEASES AND DISORDERS

BURNS AND BRUISES damage. Full-thickness burns involve the Scald Bruise
epidermis, dermis, and the subcutaneous fat A scald is a burn caused by hot liquid or steam, Bruises change color due to hemoglobin from
Burns are skin injuries due to heat, cold, layer and cause no or minimal pain. The burn often boiling water from a tap. As shown here, it red blood cells being broken down to form
electricity, friction, chemicals, light, or may be charred and black, leathery and results in a well-demarcated area of swelling and chemicals of various colors including green,
radiation. Bruises are caused by internal brown, or white and pliable. Subdermal burns redness with some blistering. yellow, and golden-brown.
bleeding into tissues from capillaries. reach down even further, to the underlying
tissues and structures. Treatment of a burn
Superficial-thickness burns affect only the depends on its site, depth, and extent. Full-
epidermis (outer layer of skin), leading to mild thickness and subdermal burns often require
swelling, redness, and pain, and rarely scar. skin grafts. Extensive burns may easily become
Superficial partial-thickness burns involve the infected and can cause massive fluid loss.
epidermis and the superficial dermis, leading
to pain, dark red or purple coloration, marked A bruise is called an ecchymosis; red or
swelling, blisters, and the weeping of clear purple bruises 3–10mm in size are called
fluid. Deep partial-thickness burns involve the purpura, and ones smaller than that, petechiae.
epidermis and whole dermis, look whiter or Treatment for bruises includes analgesics and
mottled, and are less painful due to nerve protection, rest, ice, compression, and elevation
(“PRICE”). Unexplained bruising can signal an
underlying disorder such as a blood clotting
problem, meningitis, or leukemia.

SKIN CANCER Basal cell carcinoma scaling, pinkish patch that may ulcerate, bleed, PIGMENTATION
The typical smooth pink bump of a basal cell and crust. It slowly enlarges, sometimes DISORDERS
Skin cancers are the most often diagnosed carcinoma. The center may crust and bleed and developing into a large mass, and it rarely
cancers worldwide. The most common is often described as a sore that does not heal. metastasizes. It is diagnosed by skin biopsy, Loss of normal skin color is usually due
forms are basal cell carcinoma, squamous and the usual treatment is surgical excision. to the skin’s inability to produce the
cell carcinoma, and malignant melanoma. Squamous cell carcinoma (SCC) arises from pigment melanin. This may be hereditary
the squamous cell layer. It may rarely be due to Malignant melanoma arises from the or develop later in life.
Basal cell and squamous cell carcinoma are exposure to chemical carcinogens (such as tar) melanocytes (pigment-producing cells) in the
both usually caused by cumulative ultraviolet or ionizing radiation as well as UV light. It skin. Sunlight exposure especially in childhood, Melanin is the pigment that gives the skin its
(UV) light exposure (often from sunshine and usually occurs from the age of 60 onward, but episodes of blistering sunburn, using sunbeds, color. Abnormal pigmentation is caused by
tanning beds). They are most common in people this varies. SCC accounts for about 16 percent and a family history increase the risk. It is most several conditions, including albinism and
with light skins in countries with high levels of of skin cancers. The lesion is a raised, hard, common in light-skinned people and those vitiligo. Albinism (see p.417) is a genetic disorder
UV light. They affect males more often, perhaps with many moles. Melanoma may arise from resulting in a lack of melanin pigment. This
due to differing lifetime sunlight exposures. SKIN BIOPSY a preexisting mole or appear as a new, enlarging may just affect the eyes (ocular albinism) or the
black or brown mole (see below), and is treated eyes, skin, and hair (oculocutaneous albinism).
Basal cell carcinoma (BCC) arises from the During a skin biopsy, a small sample of a by complete surgical excision. The prognosis
basal cell layer and is rare before the age of skin lesion is removed so that it may be depends on the depth and spread of the tumor. Vitiligo affects up to 1 in 50 people. It is
40. It accounts for around 80 percent of skin examined under a microscope. This may be Melanomas often metastasize and are fatal in an autoimmune disorder that is caused by the
cancers. The lesion appears as a raised, smooth, done to diagnose infections or cancers of around 1 in 5 cases. All people—not just those immune system’s antibodies reacting against its
pink or brown-gray bump with a pearly border, the skin and other skin conditions. In an with already diagnosed skin cancer—should own tissues, destroying the cells that produce
which may have visible blood vessels. It is not have yearly screening and should avoid the sun melanin. White or pale skin patches appear,
painful or itchy. The center may be pigmented by wearing protective clothing, applying commonly on the face and hands, and then
or ulcerate. It grows slowly and only very rarely sunscreen regularly, and staying out of the sun enlarge. New patches then develop, usually
metastasizes (spreads to other organs or parts in the middle of the day. all over the body. There is no cure, but
of the body). Diagnosis of basal cell carcinoma phototherapy or laser therapy may help
is by skin biopsy, and it can usually be cured by excisional biopsy, the lesion and a margin repigment areas. Camouflage cosmetics can
surgical excision (removal). of normal skin around it are completely hide smaller areas. Topical treatments may
removed. In a punch biopsy, a small cylindrical be used.
core is taken from the lesion, leaving the rest
of it behind if it is large. In a shave biopsy, Vitiligo
Depigmented patches of skin typically occur
a very thin slice of the top part symmetrically on the extremities, appearing after
of a lesion is removed. This may childhood usually before the age of 30.
be sufficient to completely remove Psychologically distressing, vitiligo may also be
a superficial skin lesion. associated with other autoimmune disorders.

Melanocyte

Melanoma on the skin Melanoma skin biopsy
Warning signs of malignant change in a mole This microscopic view of a tissue
include a change in size, shape, color, or height; sample shows cancerous
bleeding; itching; ulceration; irregular shape; melanocytes, containing brown
variable color, and asymmetric border. melanin pigment, that have invaded
the epidermal (uppermost) skin layer.

425

SKIN, HAIR, AND NAIL DISORDERS

MOLES, WARTS, CYSTS, by their appearance. They can be left alone, or NAIL DISORDERS (see p.422) can cause pitted nails. Leukonychia
AND BOILS can be surgically removed if they cause distress punctata (white flecks on the nails) is common
or become infected. A boil is a bacterial Localized infection, inflammation, and and usually due to injury to the base of the nail,
Local overgrowth of certain skin cells infection—a warm, painful lump that develops deformity of the nails is common. The disappearing as the nail grows out.
leads to a mole or a wart. A sebaceous a central yellow or white head of pus before it nails may also show evidence of diseases
cyst or a boil causes a lump in the skin. discharges the pus and then heals. Clusters of that occur elsewhere. With neglect, nails may thicken, develop
boils may interconnect to form a carbuncle. grooves, and discolor (onychogryphosis). In
Common warts are small, raised, rough lumps Recurrent boils may occur in diabetes, or those Onycholysis (loosening of the nail from the clubbing of the nail, the nails become curved
usually found on the hands or knees. Plantar with a weakened immune system. Large boils nail bed) may be caused by infection, drugs, and bulbous and the ends of the fingers
warts occur mainly on pressure points on may need incision and drainage. or trauma. Nail trauma can also result in blood eventually thicken. This can occur with
the sole of the foot, forming painful, hard collecting under the nail, leading to pain. The chronic heart and lung disease, malabsorption,
lumps. Warts (verrucae) are diagnosed by Moles are dark, pigmented lesions that blood is released by making a hole in the nail. inflammatory bowel disease, and cirrhosis.
their appearance. They often disappear by may be raised from the surface of the skin. Onychomycosis (fungal nail infection) causes
themselves, but may be treated by cryotherapy They vary in size and can develop anywhere thickened, friable, discolored nails. They are Ingrown toenail
(the use of cold to freeze them) or topical on the body. Most moles occur before the age diagnosed by examining nail clippings for fungi The nails cut into the sides of the nail bed, often
treatments containing salicylic acid. of 20 and disappear after middle age. They and treated with local or oral antifungals. leading to localized redness, swelling, warmth,
may be removed if malignant change or and pain, sometimes with pus and bleeding.
Sebaceous cysts vary in size, are smooth melanoma (see opposite) is suspected. Warning Paronychia (bacterial infection where the Minor surgery may be needed.
and round, freely move under the skin, grow signs can be easily remembered by “ABCDE”: nail and skin meet at the side or the base of
slowly, and are painless unless they become Asymmetry; Bleeding; Color change or a nail) leads to a painful, throbbing, red, hot
infected. Usually harmless, they are diagnosed variability of color; Diameter (if bigger than a swelling of the area. It responds to antibiotics
pencil eraser); Elevation. Some inherited but may need to be drained if there is pus.
conditions lead to a large number of moles. Koilonychia (spoon-shaped nails), where the
nails curve upward, is seen in people with iron-
Raised Excess deficiency anemia (see p.458). Pale nails occur
pigmented squamous in all anemias and may also be due to kidney
area cells or liver disease. The skin condition psoriasis

Pigment Excess
cells cells in
epidermis

HIRSUTISM ALOPECIA

Increased or excessive hair growth in The temporary or permanent loss of hair
areas where hair is usually absent or from the head or body may be in one
minimal, hirsutism can lead to distress area or all over the body, and may
and may have a serious cause. indicate an underlying medical condition.

Mole Wart Around 1 in 10 women develop dark, coarse Androgenic alopecia (male-pattern baldness)
Localized overproduction and build-up of Overgrowths of epidermal cells in a small area, hairs on the chin, upper lip, chest, around causes hair to recede and is most common in
melanocytes leads to a (sometimes raised) warts are caused by the human papilloma virus the nipples, or on the back, abdomen, and males. Alopecia areata is caused by autoimmune
pigmented area. As the cells are not cancerous, (HPV). Warts are passed on by direct contact or thighs. In most cases, there is no underlying attack on the hair follicles. Scalp skin disorders
they do not invade beneath the epidermis. from objects used by affected people. disorder. Serious causes include polycystic such as tinea capitis, burns, chemicals, and
ovary syndrome, hypothyroidism, Cushing’s also cause hair loss. Iron deficiency and
Raised epidermis Head syndrome, anabolic steroid use, and tumors hypothyroidism (underactive thyroid gland)
of boil that produce male hormones. Investigations may cause general hair loss. Physical or
Collection of for hirsutism may include measuring hormone psychological stress can cause telogen effluvium
sebum and Swollen levels and assessing the menstrual cycle. (diffuse general hair loss) by interrupting the
dead cells area Drug therapies include certain combined normal life cycle of the hair. Chemotherapy
oral contraceptive pills. can cause the loss of all body hair.

Cyst capsule Pus-filled Alopecia areata
(membranous sebaceous Hair lost from the scalp in patches usually regrows
wall) gland over several months, but the condition can be
permanent and body-wide.

Follicle Pus-filled
follicle

Sebaceous cyst Boil Excessive hair growth
This is a closed sac under the skin surface, filled Collections of pus in hair follicles, sometimes Shaving, waxing, plucking, electrolysis, depilatory
with accumulated sebum and dead cells. These including the sebaceous gland, boils are creams, and bleaching may help the appearance
most commonly occur on the hairy areas of the commonly caused by infection by Staphylococcus of excessive hair growth, especially on the face.
scalp, face, trunk, and genitals. bacteria and usually clear up within 2 weeks.

426

DISEASES AND DISORDERS

BONE AND JOINT DISORDERS

Bones and joints can be damaged by injury or by disease. Many conditions HOW BONES HEAL
become more common with increasing age as the bones become weaker.
Some disorders may be inherited or associated with poor nutrition and lifestyle. Bone has its own self-repair process. This
begins just after a fracture, when blood
FRACTURE to withstand impacts. There are two main types long bones are less brittle and can sometimes leaks from severed blood vessels and clots.
of fracture. A simple or closed fracture is a clean bend and crack without breaking in two; this is Over the next few weeks, the broken bone
A fracture can be a complete break, a break through a bone, but the bone ends stay known as a greenstick fracture. As long as the ends generate new tissue. The bone will
crack, or a split part of the way through inside the overlying skin. In a compound or broken parts have not become displaced or be immobilized, usually in a cast or splint,
a bone anywhere in the body. open fracture, the broken bone can pierce the abnormally angled, a fracture will usually heal if to keep the ends aligned as they heal.
skin, and there is an increased risk of bleeding the pieces are held in position; otherwise, it will
Bones can normally withstand most strong and infection. Bones may also crack without need to be reset first. Fractures are always Network of The first few days
impacts, but they may fracture if subjected to breaking apart; this is known as a hairline extremely painful. Broken bones bleed, fibrous Specialized cells called
violent force. A sustained or repeated force can fracture. If there are more than two fragments, sometimes with considerable blood loss, and tissue fibroblasts form a
also cause a fracture; long-distance runners are the break is known as a comminuted fracture. movement will provoke further pain. The bone fibrous web across the
particularly prone to this kind of injury. Bone is usually set in a cast, to relieve pain and aid break. White blood
diseases such as osteoporosis (see opposite) In children and adolescents, the long bones healing. The healing process varies from a few cells destroy damaged
can make the bones more fragile and less able of the arms and legs grow from areas near the weeks to several months, depending on the cells and debris, and
bone ends known as growth plates; these areas person’s age, the type of break, whether it is osteoclast cells absorb
can be damaged in a fracture, which may affect open or closed, and whether it has to be reset. damaged bone.
the development of the bone. Young children’s
After 1–2 weeks New woven
Bone cells called bone (callus)
osteoblasts multiply
Diagonal Horizontal and make callus
break break (new woven bone
tissue). The callus
grows from each bone
end to fill the gap.

Regrown New After 2–4 months
vessel compact In time, the blood
bone vessels rejoin across
the break. The callus
Fractured collar bone Spiral fracture Transverse fracture gradually reshapes,
This color-enhanced X-ray shows a collar bone that A sharp, twisting force may break a long bone A powerful force may cause a break across the while new bone tissue
has fractured into three separate pieces. The diagonally across the shaft. The jagged ends width of a bone. The injury is usually stable; is remodeled into
fragments need to be realigned before healing begins. may be difficult to reposition. the broken surfaces are unlikely to move. dense, compact bone.

PAGET’S DISEASE which makes the cells that produce new ABNORMAL SPINAL although the condition often runs in families.
bone (osteoblasts) work faster than normal. The CURVATURE In adults, the excessive curvature may result
This abnormality affects bone growth, resulting new bone is weak and of poor quality. from weakening of the vertebrae, obesity, or
causing bones to become deformed and The condition sometimes runs in families, but The spine normally has gentle curves poor posture. In most children, the curvature
to be weaker than normal. the cause is not known. The most common along it, but it can become excessively corrects itself as the child grows, but in severe
sites for Paget’s disease are the skull, spine, bent due to disease or poor posture. cases a corrective brace or surgery may be
Normally, bone is continually being broken pelvis, and legs, but it can affect any bone. needed to prevent permanent disability.
down and replaced by new bone, to keep the The disease most commonly causes bone pain, The spinal column has two main curves: the
skeleton strong. In Paget’s disease, the cells that which may be mistaken for arthritis, and can thoracic curve, in the chest area, and the Kyphosis
break down bone (osteoclasts) are overactive, lead to fractures of the long bones. In the skull, lumbar curve, in the lower back. Excessive
it can cause headache, pain in the teeth, and thoracic curvature is called kyphosis; curvature Lordosis
deafness resulting from affected small bones in the lower back is called lordosis. Sideways
in the ear compressing the hearing nerves; it curvature is called scoliosis. A curved spine
may also cause pressure on nerves in the neck is common in children, especially girls, and
or spine. Rarely, cancerous changes may develop in most cases there is no obvious cause,
in affected areas. Paget’s disease cannot be
cured, but it can be controlled with medication.

Thickened skull Types of spinal curvature
This color-enhanced X-ray shows abnormalities due A pronounced outward curve in the upper back
to Paget’s disease. The bone is overly thick and dense (thoracic spine) is known as kyphosis. Excessive
(white areas), and the skull appears enlarged. hollowing of the lower back is called lordosis.

427

BONE AND JOINT DISORDERS

OSTEOPOROSIS to the fragility of the bones; typical sites are the and drugs are available to slow the progression. BONE DENSITOMETRY
radial bone at the wrist, the femoral neck (hip Osteoporosis can be prevented by eating a
More common in older people, this bone), and the lumbar vertebrae, where crush healthy diet, rich in calcium and vitamin D, and A bone density scan, also called a DEXA
disorder is a loss or thinning of bone, fractures weaken the spine. The disorder can be by doing regular weight-bearing exercise, not scan, uses X-rays to measure bone density.
which increases the risk of fractures. diagnosed with a bone density test (see right), smoking, and limiting alcohol intake. Such scans are used to reveal evidence
of bone loss and help doctors diagnose
Bones stay healthy when the cells that form Normal bone Periosteum (outer membrane) osteoporosis. The varying absorption of
new bone (osteoblasts) work in balance with The inner layer is X-rays as they pass through the body is
the cells that eat worn out or damaged bone spongy bone, often Cortical bone interpreted by a computer and displayed
(osteoclasts). With increasing age this balance with a central channel Cancellous bone as an image. The computer calculates the
is gradually altered, so that less new bone is called the medullary average density of the bone and compares
formed. As a result the bones lose density, canal. The outer layer Medullary canal Osteocyte it to that of women in their 30s, when the
becoming more fragile, and are likely to break is cortical (hard) bone, (bone cell) density is the greatest. The scan is usually
with only minimal force. made of units known perfomed on the lower spine and hips.
as osteons, which
Osteoporosis is common in old age, but comprise dense layers Hip bone density scan
in some cases the process starts much earlier. called lamellae. Bone density is shown as a color-coded
Genetics, poor diet, lack of exercise, smoking, image, like this scan of a hip joint. In the
and excessive alcohol use are significant risk Cortical bone scan, the least dense areas are blue or
factors. Hormones also play a major role: in green. The most dense areas are white.
particular, a lack of estrogen (which is needed Spongy bone Lamella
to supply minerals for bone replacement) or
high thyroid hormone levels can cause more Enlarged medullary canal NORMAL OSTEON
rapid bone loss.
Osteoporotic bone Lamella
Women may develop osteoporosis after Bone density is reduced, and the medullary OSTEOPOROTIC
menopause, when their estrogen levels drop canal, through the center, is enlarged. Gaps OSTEON
rapidly. In addition, long-term treatment develop in the lamellae, adding to the Gap
with corticosteroids can cause the condition, fragility of the bone.
and people with chronic kidney failure or
rheumatoid arthritis are at increased risk of
developing it. The most common problem
associated with osteoporosis is fracture due

OSTEOMALACIA HIP DISORDERS IN (thigh bone) in the hip socket, and ranges from relatively minor trauma. This condition causes
CHILDREN a mild defect to a complete hip dislocation. symptoms in the hip or knee ranging from mild
In this painful condition, known as rickets Babies are screened for the condition at birth, discomfort to incapacitating pain, and usually
in children, the bones become softened The most common hip disorder in because it is easy to treat in the first year. If needs surgical correction. Perthes’ disease
and may bend and crack. children is known as irritable hip, and untreated, it can lead to early arthritis of the develops when the head of the femur dies
often relates to viral infection—but more hip joints. Slipped upper femoral epiphysis through lack of a blood supply, following a
Osteomalacia is due to a deficiency in vitamin significant problems do also occur. occurs in children at times of rapid growth, reduction in blood flow to the joint. The cause
D, which the body needs to absorb calcium and and is most common in adolescent boys. It is unknown, but it results in hip, knee, or groin
phosphate. These minerals give bone strength Serious problems include congenital hip involves a slippage between the growth plate pain. It is more common in boys than in girls,
and density. In healthy people, vitamin D is dysplasia, which is evident at birth. This leads of the femur and the shaft, usually following affecting mainly prepubertal children.
made in the skin. Small amounts come from oily to a misalignment of the head of the femur
fish, eggs, vegetables, fortified margarine, and Pelvis Pelvis
milk. Deficiency commonly occurs in people Pelvis Cartilage
who follow a restricted diet or cover their skin, Cartilage
and absorption is reduced in darkly pigmented Cartilage forms false
skin. Symptoms include painful, tender bones, Epiphysis joint
fractures after minor injuries, and difficulty
in climbing stairs. Treatment depends on the Growth
underlying cause and may include calcium plate
and vitamin D supplements.

Growth Growth
plate plate

Rickets Direction of Femur Abnormal hip Femur Epiphysis Femur
This child has rickets, slipped epiphysis socket
which is caused by
vitamin D deficiency. Slipped upper femoral epiphysis Congenital hip dysplasia Perthes’ disease
This causes the bones In children, the epiphysis (end of a long bone) This picture shows a severe case of hip dysplasia. In this disorder, the blood supply to the epiphysis
to become softer and is separated from the shaft by a “growth plate.” with the head of the femur failing to engage in (head) of the femur is inadequate. As a result, the
weaker, leading to pain A weakened growth plate in the upper femur can the over-shallow socket and instead forming bone breaks down and cannot engage properly
and deformity. allow the epiphysis to slip out of the hip joint. a false socket on the pelvis. in the socket, causing restriction of movement.

428

DISEASES AND DISORDERS

OSTEOARTHRITIS JOINT REPLACEMENT significantly impair quality of life. It can relieve Pelvis
pain and allow a greater range of movement,
This degenerative joint condition is the If a joint is severely damaged by disease or but the new joint will last for only 10 to 20 Original hip
most common type of arthritis, usually injury, it may be surgically replaced. This years and will then itself need to be replaced. socket may be
affecting people over the age of 50 and procedure, called arthroplasty, involves hollowed out
largely caused by joint aging. removing all or part of the joint surface and Shaft of femur and replaced
areas of damaged bone and replacing them Hip replacement
Osteoarthritis can affect any joint, although it with a prosthetic device, which is usually The top of the femur (thigh bone) is removed Head of
most commonly occurs in the hips, knees, made of metal and hard-wearing plastics or and the hip socket is hollowed out. A prosthesis femuris
hands, and lower back. In a normal joint the ceramics. Not all joints can be replaced, but is inserted into the shaft of the femur, and a new removed and
bone ends are protected by a smooth, even the knee and the hip are commonly treated socket is fitted into the pelvis. replaced with
layer of cartilage, and fluid is secreted by the in this way. Arthroplasty is a last resort, used prosthesis
synovial membranes (which line the joint only when pain or limitation of function
capsule) to allow the bones to move easily. Skin incision

In osteoarthritis, the cartilage becomes Bone Inflamed synovial Tight, thickened
frayed or torn. Friction develops, causing membrane capsule
inflammation of the membranes and leading
to heat, pain, and excess fluid production. Joint Osteophyte Inflamed
Bony growths called osteophytes develop capsule synovial
around the joint edges in response to Excess membrane
inflammation, further increasing friction Synovial synovial
and limiting the range of movement. The membrane Thickened
inflammation may come and go, but eventually fluid bone
the cartilage is so worn that bone grinds on Synovial
bone. Pieces of cartilage or osteophytes can fluid Thinned Bone
work loose within the joint, causing sudden articular surfaces in
locking. Affected joints may also give way Articular cartilage
suddenly. Exercise can be done to help limit cartilage contact
stress on the joints and increase muscle tone
to support them. In severe cases, surgery may Osteophyte
be needed to remove debris, resurface the
bone ends, or replace the joint. Reduced Cyst forming
joint space in bone

Healthy joint Early osteoarthritis Late osteoarthritis
The healthy bone surfaces are covered in smooth, Changes begin with damage and degeneration of The cartilage is worn away in places, and the bone
intact cartilage, and the whole joint capsule (the the cartilage. This leads to narrowing of the joint ends become damaged. Osteophytes and cysts
tissue enclosing the joint) is lined with synovial space, increased friction, and excess synovial fluid form, the synovial membrane is chronically
membrane, which produces lubricating fluid. production, resulting in swelling, heat, and pain. thickened, and the joint can no longer move freely.

ANKYLOSING SPONDYLITIS and Crohn’s disease, which share the same OSTEOMYELITIS AND PSORIATIC ARTHRITIS
predisposing genes. The disorder is incurable, SEPTIC ARTHRITIS
This is a form of inflammatory arthritis but physical therapy and exercise can help A form of arthritis associated with the
mainly affecting the spine and pelvis, control its course. Nonsteroidal anti- Osteomyelitis is a bone infection causing inflammatory skin condition psoriasis,
causing pain and stiffness and, in severe inflammatory drugs (NSAIDs) are used to damage to surrounding tissue. Septic this condition can be highly destructive
cases, making bones fuse together. relieve pain, and immune-modifying drugs arthritis is an infection within the joint if it is allowed to progress.
given to reduce inflammation. capsules and can damage joints.
Ankylosing spondylitis (AS) is an autoimmune This autoimmune condition affects 5–10
disease, in which the immune system attacks X-ray showing ankylosing spondylitis Bones or joints may become infected through percent of people with psoriasis (see p.422). It
the body’s own tissues. It is one of a group of This spinal X-ray shows inflammation, destruction injury or surgery, or by the spread of infection may occur in both small and large joints,
inflammatory disorders called arthropathies, of joint spaces, and joint fusion, which produce a from skin and soft tissue or via the blood. appearing predominantly in the hands, the
which affect the connective tissue in joints flexed deformity of the back. The appearance of Most cases of osteomyelitis in the developed back and neck, or a mixture of joints. In mild
and can cause progressive and irreversible late AS on X-ray is referred to as “bamboo spine.” world are due to infection by bacteria such cases, only a few joints are affected—often
damage. In the case of AS, the damage usually as Staphylococcus aureus, but tuberculosis those at the ends of the fingers or toes. In
involves the spine and pelvis. In the worst (TB) is a common cause worldwide. severe cases, many joints are involved,
cases, the joints in the spine become fused including those in the spine. Often, the arthritis
and the spine loses its flexibility; an affected The condition may be acute (develop flares up at the same time as the skin
person will have a rigid gait with permanently quickly), with many symptoms, and more symptoms of psoriasis. If left untreated,
impaired mobility. common in children, or chronic (longer- psoriatic arthritis can lead to arthritis mutilans,
lasting). In chronic osteomyelitis, the infection in which the joints are completely destroyed.
The tendency to develop AS is inherited. can cause bone tissue to die, and the dead
It typically affects men, usually beginning in tissue must be surgically removed. The bone The affected joints can no longer move at
their 20s, with pain in the lower back and marrow can also become infected. Septic all, with subluxation (slipping beneath
buttocks that is worse during the night and arthritis is usually due to S. aureus bacteria. It neighboring joints) and telescoping (collapsing
eased by walking around. Almost half of those tends to be acute, causing fever with joint pain in) of the bones. This condition is most often
with the condition have eye symptoms— and restricted movement. If fluid and pus build seen in the fingers and feet. Psoriatic arthritis
mainly iritis (inflammation of the iris), which up inside the joint capsule, the joint may be may be treated with analgesics to relieve
causes pain, redness, and temporary reduction permanently damaged. Surgery is necessary to pain and reduce inflammation, as well as with
of vision. AS is also associated with psoriasis drain the affected joint. medications to slow its progress.

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BONE AND JOINT DISORDERS

RHEUMATOID ARTHRITIS morning. RA typically flares up intermittently leading to erosion of the joint surface. Tendon common, as is anemia. People with the
and unpredictably; flare-ups can be sheaths become inflamed. As the joint condition are also at increased risk of developing
This connective tissue disorder can cause incapacitating, and may last from days to destruction progresses, the fingers may be osteoporosis and heart disease. Blood tests for
inflammation in many body systems, but months, sometimes with long symptom-free permanently deformed. Tender nodules can substances called rheumatoid arthritis “markers”
principally attacks the lining of the joints, gaps between them. If left untreated, the develop in the skin and over joints. The may help doctors to detect RA. There is no
resulting in progressive damage. disorder can spread to other areas. Joints condition can involve the heart, lungs, blood cure; treatment involves controlling the
become damaged by synovitis (inflammation vessels, kidneys, and eyes. General symptoms symptoms and using “disease-modifying” drugs
of the membrane lining the joint capsule), such as fatigue, fever, and weight loss are to slow the progression of the condition.

Rheumatoid arthritis (RA) is an autoimmune Bone Muscle Ligament
disorder in which the immune system attacks Bone
the body’s connective tissues (the fibrous Ligament Inflamed
tissues that support and connect body Ligament joint
structures). It tends to run in families and Joint
affects more women than men. Typically it capsule capsule
begins when people are in their 40s, although Synovial
it can start at any age. The first symptoms are membrane Joint Thickened
Synovial capsule synovial
painful, hot swelling
and stiffness in the fluid Thickened membrane
small joints of the Articular synovial
fingers and toes, cartilage Eroded
usually worst in the membrane bone

Rheumatoid Tendon Excess Tendon Synovial Tendon
arthritis synovial fluid
This X-ray shows RA Tendon Tendon
in the joints of the sheath fluid sheath Eroded articular Inflamed
wrist and hand, cartilage tendon
which has caused sheath
deformity of the wrist
and finger joints.. Healthy joint Early rheumatoid arthritis Late rheumatoid arthritis
The bone ends are covered with a smooth, even The synovial membrane becomes inflamed and
layer of cartilage. The joint capsule, lined with produces excess synovial fluid. This fluid contains Fluid and immune system cells build up to form a
synovial membranes, is lubricated with synovial destructive immune cells, which attack the
fluid, which allows the joint to move freely. cartilage and distort the joint space. pannus—thickened synovial tissue that produces

harmful enzymes. These rapidly destroy remaining

cartilage and bone and attack other tissues.

BONE TUMORS osteochondroma, bone cysts (holes that usually on nerves, or restrict movement, they may GOUT AND PSEUDOGOUT
form in growing bone), and fibroid dysplasia. need to be removed. Myeloma is treated with
Bone can be affected by various kinds of Primary malignant tumors (cancers arising in chemotherapy, but most other primary bone In these disorders, crystals formed from
growth, involving the bone tissue itself, the bone) include osteosarcoma and Ewings’ cancers require surgery as well as chemotherapy. chemical substances collect in the joints,
the bone marrow, or the joints. tumor, which develop from the bone itself; Secondary cancers may be treated with causing inflammation and severe pain.
chondrosarcomas, which develop from joint chemotherapy or radiation therapy, depending
Tumors that originate in the bone can be cartilage; and myeloma, which develops in on their nature and the site of origin. Gout results from excessively high levels of uric
either benign (noncancerous) or malignant the bone marrow. acid (a waste product formed by the breakdown
(cancerous). Benign bone growths are fairly Thyroid Secondary of cells and proteins) in the blood. The acid is
common and most often develop in children Secondary bone tumors are caused by gland bone cancer deposited as crystals in the joint space, causing
and adolescents. They include osteoma, cancer that has spread from other areas via Common sites inflammation and severe pain. Gout may be
the blood or lymph and they are particularly Lung of origin are the triggered by foods containing purine, including
associated with breast, lung, and prostate lung, breast, offal, oily fish, certain red wines, and some
cancer. They are more common than primary thyroid, kidney, drugs. Attacks usually affect middle-aged men.
bone cancer. Soft tissue tumors may also and bladder. and tend to last for about a week. Treatment
spread to invade nearby bone. The most involves avoiding triggers and taking medication
notable symptom of bone tumors is gnawing, Breast to lower blood levels of uric acid. Pseudogout
persistent pain that becomes worse during is caused by deposits of calcium pyrophosphate,
movement but can be relieved by anti- Kidney and is often seen in older people with joint or
inflammatory analgesics. The affected area is kidney disease. Both
often tender, and fractures may occur, in which disorders normally
the abnormal bone breaks and cannot heal. affect single joints,
causing severe pain,
Tumors may be identified by biopsy (tissue heat, and swelling.
samples). X-rays, CT or MRI scans are also used
to study the tumor. Benign tumors often need Early gout in foot
no treatment, but if they grow very large, press This X-ray shows gout
as a dense white area
Malignant tumor Prostate in the joint at the base
of the big toe; this is
Malignant tumor the most common site
Metastases (secondary deposits of cancer) may for the condition.
occur at any site in the skeleton, but most often
develop in the axial skeleton—the bones of the
skull, chest, pelvis, and spine.

430

DISEASES AND DISORDERS

MUSCLE, TENDON, AND LIGAMENT DISORDERS

The muscles enable the skeleton and organs to move. Tendons attach skeletal muscles to bones,
while ligaments connect bones to one another. Disorders affecting any of these structures can
interfere with conscious movements and other muscle functions.

MYOPATHY MYASTHENIA GRAVIS the neck). The condition often develops slowly; DUCHENNE MUSCULAR
it varies in severity as the levels of antibodies DYSTROPHY
The name myopathy means a disorder A relatively rare autoimmune condition, fluctuate. Affected muscles still function to
of the muscle fibers. Myopathies can myasthenia gravis causes fatigue and some extent but get tired quickly, although The most common form of muscular
lead to cramps, muscle pain, stiffness, weakness in muscles under voluntary they may recover with rest. Myasthenia affects dystrophy, this condition mainly affects
weakness, and wasting. (conscious) control. the eye and eyelid muscles in particular. It may boys, causing progressive, severe muscle
also affect the face and limb muscles, causing weakness and premature death.
Myopathies range from simple muscle cramps Myasthenia gravis develops when antibodies difficulties in swallowing and breathing, and
to muscular dystrophy. Some are inherited, produced by the immune system attack the loss of strength. A severe attack, or myasthenic Duchenne muscular dystrophy is an X-linked
including dystrophies (muscle-weakening) and receptors in muscles that receive signals from crisis, can cause paralysis of breathing muscles. genetic condition. Females carry the condition
myotonias (abnormally prolonged contraction the nerves. As a result, the affected muscles There is no cure, but thymectomy (removal of on one of their two X chromosomes, but are
of muscles). Others are acquired and may be only respond weakly, or fail to respond at all, a thymoma) and drugs may relieve symptoms. protected by a normal second X chromosome.
due to autoimmune inflammatory conditions, to nerve impulses. The cause is unknown, Boys, who have one X chromosome and one
such as polymyositis. The disorders may also but many affected people have a thymoma experience tiredness, disturbed sleep and Y chromosome, may inherit the faulty gene
be associated with diabetes or advanced (a tumour of the thymus, an immune gland in memory, mixed sensory symptoms, and anxiety from carrier mothers and develop the disease.
kidney disease. Some myopathies grow worse, and depression. No specific cause has yet
and become life-threatening if respiratory Myasthenia and the eyes been found, but it has been suggested that the Affected baby boys tend to start walking
muscles are affected. The treatment depends The condition typically affects the muscles that disorder may be due to a problem with the later than normal, then by the age of 3 or 4
on the cause; for many conditions, only control the eyelids, causing the eyelids to droop. way in which the brain registers pain signals. become clumsy and weak, finally losing the
supportive measures are possible. Other areas of the body may also be affected. ability to walk by the age of 12 years. The
Research also suggests some brain progressive weakness and deterioration of the
Myopathy treatment FIBROMYALGIA abnormalities that may be linked to symptoms. skeletal muscles (those attached to bones)
Treatment is mainly given to relieve symptoms of Stress and physical inactivity make the leads to deformities affecting the spine and
myopathy; it includes physical therapy and This condition, whose cause is unknown, symptoms worse, while programmes that breathing, but with modern surgical corrective
exercise programs to make muscles stronger and mainly causes muscle pains and tiredness include pain relief, exercise, cognitive treatments many affected men now live into
more mobile and analgesics to manage pain. and can last for months or years. behavioural therapy, and education can help. their 20s and 30s, or sometimes longer.

Fibromyalgia develops gradually, over a long
time, with widespread muscle pain and
tenderness. Muscles appear normal and
functional, although affected people

as tennis elbow, golfer’s elbow, and de Quervain’s a sensation of swelling, although no swelling NORMAL Damaged membrane
tenosynovitis, which result from inflammation can be seen or felt. Numbness and tingling are Fat
of tendons through repeated use. Repetitive common, and sleep may be disturbed by the
CHRONIC UPPER LIMB strain injury (RSI) is often due to occupational symptoms. The disorders are often relieved by
SYNDROME overuse. Symptoms include gradual onset of rest, gentle exercise, and modifying the activity
pain, often difficult to pinpoint to one area, and that brings on the condition.
This name is used for a group of disorders
affecting the hands and arms, such as Lower end of humerus ABNORMAL
repetitive strain injury (RSI), which cause
pain and restriction of movement. Area of damage to articular surface Effects of muscular dystrophy
Progressive destruction of muscle is seen here at
The cause is often thought to relate to overuse Osteoarthritis at the elbow the cellular level, as muscle cells undergo damage
of the arm. Certain inflammatory conditions Abnormal stresses on a joint can predispose to the to their outer membranes and are replaced by
are also sometimes included within this group. development of osteoarthritis. Here, stress on the connective tissue and fat.
They include carpal tunnel syndrome (see elbow from pneumatic drilling has led to damage
p.434), which affects the hand and forearm of the articular cartilage and underlying bone.
due to nerve compression at the wrist, as well

431

MUSCLE, TENDON, AND LIGAMENT DISORDERS

anatomically; Achilles tendinitis, for example, Humerus Inflamed supraspinous
affects the back of the heel, causing pain on tendon
TENDINITIS AND putting the foot to the floor. FIRST AID TREATMENT
TENOSYNOVITIS Clavicle
Tenosynovitis can arise as a degenerative (collarbone) Injuries to muscles, tendons, or ligaments
These conditions involve inflammation of disorder or in connective tissue disease, arthritis, can be treated quickly and easily by a
the tissues that connect muscles to bones, or an overuse injury, or with tendinitis. The most Acromial process of technique called PRICE—this stands for
often due to injury or overuse. common example is de Quervain’s tenosynovitis, shoulder blade Protection, Rest, Ice, Compression, and
which affects the tendon sheath enclosing the Elevation. Protection helps prevent further
Tendons are fibrous tissues that attach muscles two muscles that move the thumb outward Tendinitis injury; rest relieves the injured area; an
to bones, enabling the bones to move when from the hand. This condition causes pain, Tendons transmit the pull of muscles to bones. ice pack every few hours reduces pain,
muscles contract. Inflammation of the tendons swelling, tenderness, and difficulty in gripping. Injury or overuse can cause inflammation or a inflammation, and bruising; compression
is called tendinitis; this often occurs together Tenosynovitis may also cause joints to stick, as tear in the tissues, resulting in pain and sometimes with an elastic bandage helps reduce
with tenosynovitis, inflammation of the sheath in “trigger finger.” In both conditions, treatment a crackling sensation as the limb moves. swelling; and elevation (raising the limb)
of tissues enclosing a tendon. Both conditions may involve rest or modifying the use of the also reduces swelling, by allowing excess
cause pain on movement, sometimes with a tendon with braces, splints, or supports, as fluid and waste from the body’s repair
“catch” point during a limb motion, when the well as analgesics, anti-inflammatory drugs, process to disperse. PRICE reduces blood
affected tendon moves. and gradual return to exercise. flow to the injury and therefore reduces
bleeding, bruising, and swelling.
Some tendons form pulleys, as seen in the Inflammation
shoulder, where the supraspinatus tendon Treatment for strains and sprains
passes in a groove over the joint; an inflamed The PRICE technique includes applying an ice
tendon that “catches” will cause a painful arc of pack and elevating (raising) the affected area
movement. Tendinitis is generally referred to above the level of the heart.

Tendon sheaths Tendon sheath
Tendons
Tenosynovitis
The synovium, the protective sheet of tissue that
covers some tendons, produces fluid to keep the
tendon moving smoothly. Inflammation of these
tissues causes pain and tenderness.

LIGAMENT SPRAINS People taking part in sport or exercise are MUSCLE STRAINS Pelvis
AND TEARS advised to do “warm-up” exercises to protect AND TEARS
their ligaments. These tissues are not easily
Ligaments are bands of connective tissue torn owing to their strength, but they can be Excessive stress on muscles can cause Femur
that hold bones together; they are tough damaged by a fall or a sudden twisting or strain (sometimes referred to as “pulling Tendon
and thick, but not very stretchy, so are wrenching movement. Injuries range from a a muscle”) or even a tear in the muscle.
prone to tearing. sprain (minor tear) to a rupture (a complete Semi-
break in the ligament). The wrists and ankles Muscles contract in order to move joints. They tendinosus
Ligaments can stretch gradually under tension, are common sites of injury. Symptoms come comprise groups of parallel fibers that move
as gymnasts and ballerinas show by stretching on suddenly and include pain, swelling, and relative to one another and grip one another muscle
their ligaments gradually during their training restricted movement in the joint. Damaged like interlocking ladders. Muscle injuries are Site of tear
to achieve extreme body positions. Ligaments ligaments heal relatively slowly because their common and range from a mild strain, in which
also become stretchier in pregnancy, to allow blood supply is not as rich as that of muscle. fibers are pulled apart lengthwise but without Vastus lateralis
the pelvis a little more “give” during childbirth. Mild sprains can be relieved by PRICE (see tearing, to a complete tear, which can cause muscle
right), but severe, incapacitating injuries need pain, bleeding, and dramatic swelling. Strains
medical attention to prevent joint dislocation. are often caused by over-stretching or Torn hamstring
over-contracting a muscle, in sports or heavy The hamstrings are the muscles at the back of the
Sprained ankle Tibia physical work. Some strains are chronic, due thigh, which bend the knee and pull the leg back.
The ankle is prone to sprains if the foot to repeated over-stressing of a muscle. Hamstring injuries are often seen in athletes who
twists suddenly. Common injuries are Fibula do a lot of sprinting or jumping.
lateral ligament sprains, in which the Injury is particularly common during
foot turns inward, or medial ligament Torn lateral sudden changes in directional force, such as
sprains, in which it twists outward. ligaments twisting suddenly while running, during falls,
and when lifting heavy objects. Injuries need
Talus immediate treatment with PRICE (see above),
and the affected muscle will have to be kept
Navicular still for a few days. Muscles have a rich blood
supply, so they heal relatively quickly, but
Calcaneus recovery time also depends on the severity of
the injury, the natural variation in healing time
between individuals, and the level of normal
activity required of the muscle.

432

DISEASES AND DISORDERS

BACK, NECK, AND SHOULDER PROBLEMS

Disorders of the spine and shoulders are common but can be disabling. The lower back is vulnerable
to damage since it supports most of the body’s weight and is under continual pressure from bending
and twisting movements. The shoulder is also prone to problems as the body’s most mobile joint.

fibers, to major trauma, in which neck Ligament Disk
ligaments are torn. The sudden pull of tear
muscle and tendon on bone may break
WHIPLASH pieces off the ends of the vertebrae Disk pinched
(spinal bones). Nerves may be between
This term is used for a range of injuries damaged, causing pain in the neck, vertebrae
caused by sudden back-and-forth shoulders, and arms, and possibly
movements of the neck. dizziness and disturbed vision; some Cervical
people also suffer memory problems spine
Whiplash commonly occurs in traffic and depression. In the hours following Ligament
accidents, due to deceleration: the sudden a whiplash injury, bleeding occurs in the tear
impact first forcibly flexes the neck as the head tissues, and tissue swelling and muscle spasm
is thrown forward, then forcibly extends the follow; the injury reaches its peak in the first 48 1 Hyperextension 2 Flexion
neck as the forward momentum of the head is hours. It can take many weeks or months for If hit from behind, the head rapidly moves Following hyperextension, flexion of the
stopped by the body, and the head rebounds whiplash to get better. Treatment includes backward then forward. Whiplike backward vertebrae occurs as the head’s momentum carries
backward. The severity of the injury varies from anti-inflammatory drugs and physical therapy. motion hyperextends the cervical vertebrae. it forward and causes the chin to arc down.
small strains, with tearing of a few muscle

TORTICOLLIS FROZEN SHOULDER Inflammation of the fibrous tissues leads to
frozen shoulder, also called adhesive capsulitis.
Also known as wry neck, torticollis In this condition, the tissue around the Although the cause is unknown, the disorder is
usually involves spasm of the muscles in shoulder joint becomes inflamed, stiff, more common in people who also have other
the neck, which pulls the head to one side and painful, severely limiting movement. inflammatory joint or muscle conditions, and
and results in pain and stiffness. in those with diabetes. It begins gradually, with
In the shoulder joint, the humerus (upper arm pain and inflammation in one area or muscle
Torticollis is thought to be due to pulling on the bone) and end of the scapula (shoulder blade) group, but then progresses around the joint,
deep ligaments of the neck, causing a muscle are enclosed in a capsule of fibrous tissue filled with adhesions (bands of scar tissue) forming
spasm. It may occur in babies due to a difficult with fluid that enables the joint to move easily. between the tissues. The pain can disturb sleep
birth or an awkward position in the womb. In and limit movement. In a typical case, there
adults, it may be caused by damage to the joint Calcification of rotator cuff are three stages: slow, painful “freezing” of the
at the skull base, or possibly by a nerve disorder. shoulder over several weeks or months; a
Often, torticollis can simply be due to sleeping Inflammation of the shoulder joint “frozen” stage lasting for months, when the
in an awkward position; in this case, it usually Chronic inflammation of the tissues around the pain is less but the stiffness is severe; and then
improves in 2 or 3 days and can be relieved by shoulder joint can cause calcium deposits to form several weeks of “thawing.” Treatment involves
anti-inflammatory or antispasmodic drugs, in the tissues; these show as white areas on X-ray. physical therapy, analgesics, and occasionally
massage, and rest. Further treatment may be corticosteroid injections into the shoulder.
needed for more permanent torticollis. however, it also makes the joint unstable, or
DISLOCATED SHOULDER liable to dislocate under pressure. Dislocation
Torticollis is most commonly due to falling or impacts in
Spasm of the large muscle around the side of the Dislocation is an injury in which a joint is sports such as football. It can also be caused
neck causes torticollis, with a resulting tilt of displaced from its normal position. The by inherited loose joints. A dislocated shoulder
the head to one side. shoulder is particularly prone to this is painful and swollen and may look deformed.
problem, usually due to sudden impacts. An X-ray will be needed to confirm and assess
the injury. Treatment involves manipulation to
The shoulder is a ball-and-socket joint in which move the bones back into place.
the head of the humerus (upper arm bone) sits
in a shallow socket at the end of the shoulder Dislocation of humeral head
blade. The shoulder bones are kept in place by
the rotator cuff, a group of strong muscles X-ray showing shoulder dislocation
around the joint. This structure allows the arm This X-ray shows an anterior (forward) dislocation.
a wide range of movement in many directions; In most cases the bone is displaced forward,
because the rotator cuff is weakest at the front.

433

BACK, NECK, AND SHOULDER PROBLEMS

LOWER BACK PAIN sitting or standing, or lifting heavy objects in a DISK PROLAPSE herniate (protrude) through it; this is often
way that does not safeguard the back. Injury to AND SCIATICA called a slipped disk. The problem is more
Most people suffer back pain at some the structures of the spine and back as a result common in the lumbar disks (those in the lower
point, often due to strain on the muscles of excessive strain may be caused by twisting, The vertebrae (spinal bones) are separated back), which are subject to the most force—
and ligaments; the lower back is the area bending, or lifting. The lumbar area of the by disks of soft tissue; if one of the disks especially if they have started to degenerate due
most commonly affected. back, below the waist, is especially vulnerable slips out of place or ruptures, this can put to age. It may occur suddenly or slowly. Sudden
to back pain because it already bears much of pressure on a nerve and cause pain. slippage may occur after lifting or injury; and it
Although there are many theories about lower the body’s weight. Pain may arise from the may cause pain or difficulty in moving.
back pain, and many studies have been done, muscles, ligaments, vertebrae (spinal bones) or The disks that separate the vertebrae are
the definite cause is unknown. MRI scans can the disks between the bones, or the nerves, composed of a tough, fibrous coating and a A prolapsed disk may press on the nerves
show marked damage to muscles and joints although muscle strain is most common. softer, jellylike core. Sometimes, excessive stress leading from the spinal cord, causing sciatica:
in people who have no back pain, while scans on the back can cause a disk to get pushed out burning, tingling pain in the sciatic nerve, which
of people with debilitating pain may fail to In most cases, an affected person can of position. If the disk is squeezed, the outer travels via the buttock, down the back of the
show any abnormality at all. relieve back pain with heat, anti-inflammatory coating may rupture, and the soft core may leg, to the foot. In many cases, gentle exercise
analgesics, and gentle exercise. For pain that is and analgesics bring recovery within 6–8 weeks.
It is important to avoid behavior that might more severe or that lasts for more than a few More serious cases may require physical
lead to back injury, such as poor posture when days, medical treatment or physical therapy therapy or surgical repair of the disk.
may be needed.
MANAGING BACK PAIN
Spinal nerve Nucleus pulposus Protruding Annulus fibrosus
After a back injury, a person should remain (gelatinous core) core pressing (fibrous outer layer)
physically mobile and resume normal
activities as soon as possible. Back pain Annulus on nerve Spinal nerve
generally gets better within 2 or 3 weeks fibrosus
with exercise and pain relief. However, a (fibrous outer
person with chronic back pain may need layer)
treatment with physical therapy and back
rehabilitation programs in addition to Vertebra Spinal cord
analgesics. Addressing lifestyle issues such
as losing weight, and learning a method of NORMAL
using the back muscles safely, such as the
Alexander technique, can help ease the
pain and prevent recurrences.

Treatment for back pain Disk prolapse Pressure on
Treatments include medication for pain and A prolapsed disk may push into the center of the spinal cord
muscle spasm, physical therapy to strengthen spine, pressing on the spinal cord and the roots of
the back, and advice on back health. the nerves leading from it. In the lumbar spine PROLAPSED DISK
this can affect nerves to the legs, causing sciatica.

SPINAL STENOSIS SPONDYLOLISTHESIS

Stenosis, or narrowing, of the spinal Vertebra The forward slippage of one vertebra
canal can compress the spinal cord or over another is called spondylolisthesis;
nerve roots; this condition is usually due it usually causes no symptoms, although
to the effects of aging. at worst it can compress the spinal cord.

Age-related changes to the spine may begin Degeneration Spondylolisthesis may result from a congenital Scan of spine showing spondylolisthesis
in the mid-30s, but obvious symptoms are Stenosis spinal deformity (one that is present from Spondylolisthesis most often affects the lumbar
unusual before age 60. Stenosis begins with birth), or may develop during growth in mid- vertebrae, in the lower back, as seen in this scan.
stiffening of the joints between the vertebrae X-ray of the spine to late childhood. However, most cases occur The overhang where the upper vertebra has
and the formation of bony growths called This color-enhanced X-ray shows spinal stenosis in adults and result from degenerative changes slipped is clearly visible.
osteophytes on them. These growths encroach caused by severe degeneration of the spine. The to the joints between vertebrae, which alter the
on the spinal canal and the foramina (gaps red areas are bones distorted by osteophytes, and angle of the bones and allow higher vertebrae
through which the nerve roots exit the spine), the greenish area is the spinal canal. to slip over lower ones. In most cases there are
narrowing the spinal canal. Stenosis is most no symptoms, but some people have pain,
common in the lumbar spine, and can lead to stiffness, or sciatica (see above). If there is
pain, cramping, and weakness in the back, coexisting spinal stenosis (see left), symptoms
neck, shoulders, legs, or arms. An affected may be worsened by the narrowing. Severe
person may be given anti-inflammatory drugs cases (in which the upper vertebra is more
and physical therapy, but serious cases may than 50 percent out of line) may cause
need decompression surgery, in which bone or significant pressure on the spinal cord, and
tissue is removed to ease pressure on the cord. decompression surgery may be needed.

434

DISEASES AND DISORDERS

LIMB JOINT DISORDERS

Problems involving the muscles, tendons, or other soft tissues around the joints are often caused
directly by the way we use those joints. They can result in considerable pain, but many of them
get better by themselves or need only rest and treatment at home.

EPICONDYLITIS area is tender to touch, with pain that is made CARPAL TUNNEL addition to the nerve, 10 tendons pass through
worse by movement. In golfer’s elbow, lifting SYNDROME the space. Carpal tunnel syndrome occurs
This condition includes tennis elbow and the arm with the palm upward will worsen when the nerve is compressed. This may be
golfer’s elbow and involves inflammation pain; in tennis elbow, lifting the arm with the Compression of the median nerve, which caused by swelling of the tendons, or by fluid
of the epicondyles, the bony protrusions palm downward makes it worse. passes through the carpal tunnel in the collecting in the carpal tunnel due to wrist
on either side of the elbow joint. wrist, causes carpal tunnel syndrome. arthritis, hormone fluctuations, thyroid
Pain moves down one side of the arm, problems, diabetes, or overuse. The pressure
Tennis elbow, affecting the outer epicondyle, into the hand, with tingling in the forearm and The median nerve passes down the forearm to results in pain, loss of grip, tingling in the
and golfer’s elbow, which develops in the inner heat, pain, and swelling over the epicondyle. the hand, where it operates the muscles at the thumb, first two fingers, and half the ring finger
epicondyle, usually result from overuse of the Treatment involves resting the arm and using base of the thumb and controls sensation in and, if severe, wasting of the thumb muscles.
muscles that attach to the bone at these analgesics. A splint may help, and braces the thumb half of the palm. En route it passes In mild cases, it is treated with rest, analgesics,
points, or occasionally from direct injury. The are used to take the strain off the muscles. through the carpal tunnel, a space between the and splints. Corticosteroid injections are
damage causes inflammation of the tendons Physical therapy may be recommended and wrist bones that is enclosed by a ligament. In sometimes given to relieve inflammation. In
that attach the muscles to the epicondyles. corticosteroid injections given for severe pain. severe cases, decompression surgery is used
Tennis elbow classically arises from recurrent to relieve pressure by dividing the ligament.
serving in tennis, and golfer’s elbow from the
golf swing, but the conditions are far more Carpal ligament Median nerve
commonly due to other overuse injuries. The
Carpal bone Carpal tunnel
Skin
Median nerve

Tennis elbow Tendon sheath
Epicondylitis can affect both sides of the elbow
simultaneously. Symptoms include a painful, Carpal
reddened area around the joint. ligament

GANGLION KNEE JOINT EFFUSIONS Cross section of carpal tunnel Tendon
This cross section shows the nerve in yellow
Most often found on the wrist, ganglions Also known as “water on the knee,” an immediately beneath the carpal ligament and just
are soft, harmless swellings that often effusion on the knee can cause swelling above the 10 flexor tendons, which act to bend
disappear by themselves eventually. and, sometimes, stiffness and reduced the fingers, thumb, wrist, and palm.
ability to use the joint.
Ganglions are cysts that form just under the
skin, over a tendon sheath. They often occur Joints contain bone ends inside the synovial BURSITIS buildup called bursitis. The area may become
close to joints, in which case they tend to be membrane, which produces the synovial fluid red, painful, and swollen. Bursitis is common
connected to the joint; typical sites are the that lubricates the joint. Sometimes an Inflammation of a bursa, one of the small around the knee and elbow, perhaps because
feet, wrists and hands, most commonly the effusion—a collection of excess fluid—can pads that provide cushioning in joints, these joints often suffer injury. An olecranon
extensor (upper) side of the wrist. Ganglions accumulate around a joint. An injury, or an can cause pain and obvious swelling. bursa, at the back of the elbow, can become
contain synovial fluid, a thick, clear, gel-like infective or inflammatory disorder (such as very large because the loose skin allows
substance, from inside the joint. If they cause osteoarthritis or gout), can cause the condition Bursae are lined with synovial membrane and expansion. Bursae usually settle by themselves;
no symptoms they can be left to disappear by provoking the membrane to produce filled with jellylike synovial fluid. They act as they can be drained but often refill.
excess synovial fluid. cushions between the moving parts of most
by themselves. If they joints. Injury or infection of a bursa can cause
cause pain or impede The knee is particularly prone to effusion as the lining to produce excess fluid leading to a
movement, they can be it bears considerable downward and rotatory
drained or removed. forces and is therefore prone to wear and Housemaid’s knee
injury. Knee effusions tend to cause obvious, Bursitis in the knee, also known as housemaid’s
Ganglion soft swellings, with pain, and it may be difficult knee, often occurs in people who spend a lot of
Like most ganglions, this to put weight on the leg. Treatment depends time kneeling, such as gardeners.
swelling is situated on the on the cause; it may involve draining the excess
extensor (outer) surface fluid and/or giving corticosteroids or anti-
of the thumb joint. inflammatory drugs to reduce the inflammation.

435

LIMB JOINT DISORDERS

CHONDROMALACIA OSGOOD-SCHLATTER Osgood-Schlatter ACHILLES TENDINITIS
DISEASE disease
Chondromalacia patellae is pain at the This photograph shows The Achilles tendon connects the muscles
front of the knee, which is probably Usually seen in active teenagers, this a prominent tibial of the calf to the ankle, and may often
related to overuse and is most often seen condition is caused by inflammation at tuberosity in a person become inflamed in athletes and runners.
in active young people. the front of the tibia (shinbone), just with Osgood-Schlatter
below the knee. disease. Recurrent Achilles tendinitis results from small tears in the
The pain in chondromalacia may be caused small fractures lead to tissue as the foot hits the ground with excessive
by chronic friction where the patella (knee Osgood-Schlatter disease usually occurs during a bony lump, which is force—typically when someone is running or
cap) passes back and forth over the knee joint adolescent growth spurts, often in teenagers usually very painful if jogging on hard or rough ground. Pain and
as it flexes and extends. In adolescents, the who do a lot of sports. It develops at the tibial it is knocked. swelling develop at the back of the ankle, and
condition can be very painful but is essentially tuberosity, a bony point at the top of the tibia the ankle itself may swell. The inflamed tendon
harmless. It may be relieved by rest and where the quadriceps muscles, at the front of the Bony prominence is particularly painful if it has been stretched
physical therapy and, because it usually clears thigh, attach to the tibia via the patellar ligament (as it is when a person flexes the heel to “push
up over a couple of years, most physicians (which connects the kneecap to the tibia). It is of shin splints—stress fractures of the growth off ” from the ground during a stride). In many
prefer to avoid surgery that could scar the thought to result from excess strain on tibial plate at the end of the tibia. As the body tries cases, the condition can be relieved by rest,
joint. Chondromalacia, which is sometimes tuberosities as the long bones of the leg grow to heal the fractures, it produces new bone applying an ice pack to the area, and taking
known as runner’s knee, is also common in more rapidly than the muscles can lengthen. growth at the tuberosity, enlarging the point analgesics. If it persists, treatment may include
adults, particularly in women over 40 years into a prominent lump that is tender to touch physical therapy or temporarily fitting an
of age. In adults, the condition can usually Repeated stress from contraction of the and may be so painful that it prevents exercise orthosis into the shoe—a device such as a
be relieved only by exercises, rest, ice, overstretched quadriceps is transmitted to the altogether, particularly when a splint has just heel pad or cup that reduces the stress on the
and therapy. tuberosity, causing pain and swelling. In the formed. However, the condition does clear tendon as the foot is placed to the floor. The
most severe cases, this results in the formation up after a couple of years, and often needs no Achilles tendon has a relatively poor blood
Achilles treatment except rest, ice, and analgesics. supply, so healing tends to be slow.
tendon PLANTAR FASCIITIS
is caused in a similar way to Achilles tendinitis Achilles tendinitis
Inflammation The plantar fascia is a thick band of (see right), by repeated overstretching. Common If an Achilles tendon is severely inflamed, as
tough, fibrous tissue running beneath the in people who do a lot of walking over rough shown here, excess tissue fluid collects and gravity
Plantar sole of the foot and supporting the arch; ground or jogging, it can be degenerative and causes it to move downward, resulting in swelling
fascia inflammation here can cause severe pain. can accompany inflammatory arthritis, obesity, of the ankle and heel.
osteoarthritis, and diabetes. Pain occurs when
The plantar fascia is the continuation of the the sole of the foot is stretched, and is usually
Achilles tendon and connects the heel bone to felt most severely beneath the heel; it is
the base of the toes. Inflammation in this tissue described as “walking on marbles.”

Treating plantar fasciitis Initial treatment includes rest, ice packs,
The pain from plantar fasciitis most commonly and analgesics. Exercises may be prescribed to
stretch the tissues gently. Some people may
develops near the back of the sole, where be given orthoses, devices that fit in the shoes
the plantar fascia attaches to the to relieve the stretch on the fascia when the
calcaneus (heel bone). foot is used. Severe cases may be treated with
an injection of corticosteroids and local
anesthetic into the affected area.

FOOT DEFORMITY disorders. There are usually no symptoms, but HALLUX VALGUS (BUNION) wearing tight, pointed shoes, which tend to
it can cause problems with fitting shoes. Club compress the toes into an angled position.
Abnormalities in the bones, muscles, and foot is inward twisting of one or both feet, and Some people have a structural deformity The affected toe may develop arthritis. Some
ligaments of the foot can distort the is present from birth; the cause is unknown. of the joint at the base of the big toe, people have difficulty finding shoes that fit
shape and cause problems with function. Most cases are treated with minor surgery, which leads to the formation of a bunion. over the bunion. Pads, orthoses (corrective
along with physical therapy and special shoes. devices), and comfortable shoes may help
The valgus deformity begins with the big toe relieve the pressure, but
The shape of the feet develops as a child Flat foot gradually turning inward, sometimes with the if symptoms are severe,
grows, and the bones, ligaments, and fascia This image shows flattening of the arch due to other toes also bending at an angle. As the big surgery will be needed to
(connective tissue) form an arch in the sole; collapse of the bony structures under the weight toe moves out of position, the joint between remove the excess bone
this structure gives flexibility and acts as a of the patient. The entire sole of the foot can be its base and the head of the first metatarsal and realign the toe.
shock-absorber. Structural disorders can seen in contact with the ground. bone (in the body of the foot) is exposed,
affect the shape of the arch, causing flat or becoming swollen and painful. Inflammation Enlarged part
high-arched feet. In flat feet, or pes planus, the of the bursa over the joint adds to the of joint
arch collapses or may never have developed, enlargement and pressure. The resulting bony
and the entire sole contacts the ground on lump is called a bunion. The condition tends Bunion
walking. It can lead to pain, but arch supports to run in families. The cause is complex and Bending of the big toe
will help. Pes cavus is a condition in which the involves abnormal action of the foot—possibly causes deformity in the
arches are abnormally high; it may be inherited combined, in some cases, with years of bone and thickening
or may be acquired in some muscular or nerve of the soft tissues
around the toe joint,
forming a bunion.

436

DISEASES AND DISORDERS

CEREBROVASCULAR DISORDERS

The cerebrovascular system comprises the blood vessels that supply the brain. It is prone to
conditions that can affect blood vessels elsewhere, such as blood clots and atherosclerosis,
but the effects on the brain are specific and sometimes catastrophic.

STROKE stream until it lodges in a cerebral artery already relatively common for strokes to affect one time, function may gradually return, and with
narrowed by atherosclerosis. A minority of whole side of the body (hemiplegic stroke) rehabilitation it is possible to relearn skills. The
A stroke causes sudden, irreversible strokes are hemorrhagic (caused by bleeding), initially, leading to one-sided paralysis. Speech, risk is reduced by not smoking and by
damage to areas of brain tissue due to due to a tumor or to blood vessel malformation. swallowing, and vision may be affected, as lowering blood pressure and cholesterol
disturbance of the blood supply—it is may personality, memory, and mood. The levels. Sometimes early treatment with
the brain’s equivalent of a heart attack. Stroke occurs if the damage caused is not damaged brain swells, and it can be weeks or clot-busting drugs can minimize or reverse
completely reversed within 24 hours. It can months before the swelling settles. During this the damage.
The brain needs a rich supply of oxygen and involve small or large areas of the brain; it is
nutrients from the blood in order to function LONG-TERM EFFECTS
properly. If the blood supply is interrupted, Tiny blood vessels can become OF A STROKE
brain cells can fail and die, interfering with the blocked as a result of prolonged
physical or mental function controlled by the high blood pressure or diabetes The long-term effects of a stroke depend
affected part of the brain. This is cerebral on which part of the brain is damaged,
infarction. Most strokes are atherotic, occurring Carotid Posterior cerebral artery whether the damage is permanent, and
when a thrombus (a piece of atherosclerotic artery how well the brain learns new pathways
material) breaks off from the heart or a large Basilar to accomplish tasks. Even a major stroke
cerebral artery and flows along the blood artery may be followed by gradual but dramatic
recovery. Speech is commonly affected,
Hemorrhage External particularly in terms of finding and forming
carotid words. Stroke may also alter personality,
Blood vessel and increased emotional difficulties and
artery depression are common aftereffects.
Bleeding within the brain
Rupture of blood vessels in the brain is termed Fatty deposits in Internal Facial paralysis
intracerebral hemorrhage. This is the least an artery cause a carotid The facial paralysis sometimes seen with
common type of stroke, usually resulting from a clot (thrombus) to stroke usually affects just one side, preventing
tumor or preexisting blood vessel abnormality. form, which may artery the eye and mouth from closing fully.
block blood flow
Vertebral artery
in the brain. Common

carotid artery
Blood flow

Blood flow A piece of clot material
(embolus) may become

lodged in a vessel

Blocked blood vessels supplying the brain

Blockages can have various causes: most often

plaques (fatty deposits on blood vessel walls),

but also emboli (free-floating blood clots) or

narrowing of blood vessels due to disease.

brain tissue results. TIAs can last for seconds Blocked blood
or hours, and may involve any of the functions flow
that are affected in stroke. It is a warning sign
TRANSIENT ISCHEMIC for stroke—more so if prolonged or frequent. Dispersed
ATTACK TIAs therefore require urgent investigation, particles
including scans of the heart and carotid
In this condition, brief interruptions to arteries (which supply the brain), to find the Embolus Blood flow
normal cerebral blood flow result in a source of the material causing the blockage. resumes
sudden, temporary loss of function. Temporary
The risk factors for TIA, as for stroke, are blockage Dispersal of
If stroke is the brain’s equivalent of a heart high blood pressure, smoking, diabetes A TIA begins when a blockage
attack, transient ischemic attacks (TIAs) are the (especially if control is poor), and high fragment of a blood The blockage is moved
equivalent of angina. The process of a TIA is cholesterol, all of which increase the risk of clot (an embolus) by the pressure of the
like that in a thrombotic (clot-related) stroke, atherosclerosis and of fatty deposits forming in detaches from a blood blood building up
except that in TIA the blockage in the blood blood vessels. Treatment aims at reducing the vessel and lodges in behind it. Oxygenated
vessel is temporary and possibly only partial, risk factors and thinning the blood with aspirin one of the small blood blood can then reach
and clears itself before permanent damage to or warfarin to prevent clots from forming. vessels in the brain. the area of the brain
that has been starved
of oxygen.

437

CEREBROVASCULAR DISORDERS

SUBARACHNOID be present from birth, but trauma can also SUBDURAL blood called a hematoma, which presses on
HEMORRHAGE damage blood vessels, causing them to HEMORRHAGE brain tissue. Severe bleeding causes pressure
hemorrhage. The bleeding causes a sudden, on the brain, with rapid loss of consciousness.
This dangerous condition involves blood severe “thunderclap headache,” with vomiting, A subdural hemorrhage occurs when
leaking between the inner two of the confusion, intolerance of light, and, in severe blood leaks into the space between the Acute subdural hematomas are usually
three meninges—the layers of membrane cases, coma and death. Warning headaches outer two of the three meninges—the caused by severe head injuries. They are most
covering the brain. may occur before the blood vessel ruptures. membranes covering the brain. often seen in young men, and in babies—
A CT scan may be done to find the source of possibly as a result of shaking (“shaken baby
Subarachnoid hemorrhage occurs when an bleeding, and the affected vessels surgically Subdural hemorrhage usually results from tears syndrome”). Chronic subdural hemorrhages
artery near the brain surface suddenly ruptures repaired. However, full recovery does not in the veins that cross the subdural space, cause gradual confusion and decline in
and blood escapes into the subarachnoid always occur, and almost half of cases are fatal. between the dura mater (the outermost of the consciousness; they are usually seen in older
space, between the inner two meninges—the meninges) and the arachnoid mater. This leads people, in whom they may be mistaken for
arachnoid mater and the pia mater. In most Capillaries to acute, severe bleeding or a slow, chronic dementia, or in people who abuse alcohol.
cases, hemorrhage results from the rupture of a bleed. The bleeding produces a pocket of This is because age and alcohol are associated
berry aneurysm—a swollen, weakened area at NORMAL with a tendency to cerebral shrinkage, which
the join between two arteries in the brain—or Scalp stretches the veins crossing the meninges and
malformed blood vessels, problems that may ABNORMAL Abnormal possibly makes them more liable to rupture.
knot of Skull
Blood vessel vessels LOCATION
Dura mater
Neck of aneurysm Arteriovenous malformation Blood
Abnormally formed arteries and veins are Arachnoid
Berry aneurysm connected in a tangled knot. High-pressure matter Subdural hemorrhage
A berry aneurysm is a swelling in a blood arterial blood meets low-pressure venous blood The hematoma, or collection of blood, between
vessel wall that develops at a weak point in the at these points, so they are prone to bleeding. Pia mater the outer two layers exerts pressure on the brain.
join between two blood vessels. Berry aneurysms It may grow rapidly within hours, or may take
are often found at the base of the brain. Normal weeks or months to increase in size.
The brain is enclosed in three layers of membrane
called meninges: the dura mater, arachnoid mater,
and pia mater. These layers carry sensitive nerves
and blood vessels over the brain’s surface.

MIGRAINE beyond the age of 50. The cause is not fully Migraine attack HEADACHE
understood, but one theory suggests that This scan shows
Migraine is a recurrent and often severe migraine starts with sudden constriction of different levels of brain Most headaches are tension headaches,
headache, usually on just one side of the blood vessels in the meninges (membranes activity during a resulting from stress; a more painful form
head, which occurs with disturbed vision, covering the brain), causing a transient slight migraine. The red and is cluster headache, with brief attacks
nausea, and other abnormal sensations. ischemia, followed by a “flush” or dilation, yellow areas show high happening several times a day.
which stretches the sensitive veins and nerves activity; areas of gray
Migraine affects more women than men and and leads to pain. It is typically triggered by and blue indicate Tension headache is a feeling of constriction
tends to run in families. The condition can first factors such as stress, hunger, fatigue, and low activity. across the forehead, brought on by tightness
appear at any age, although it rarely starts certain foods and drinks including chocolate, in the muscles of the scalp and neck. It is often
red wine, and caffeine. In women, attacks or behavior. The premigraine aura (if present) worse at the end of the day and is increased
Prodrome may last may be associated with hormone fluctuations often consists of visual disturbances such as by fatigue or stress. The pain can usually be
for hours or days and often occur before menstrual periods. blurred vision and seeing flashing lights; relieved with analgesics and relaxation.
abnormal sensations such as numbness or pins
Aura typically lasts Migraine attacks are often disabling and and needles; loss of balance or coordination; Cluster headache affects more men than
for up to an hour may last for up to 3 days. They typically have and difficulty speaking. The headache is women, and is an excruciating one-sided pain
four stages—the prodrome (warning signs), typically a throbbing pain on one side of the around one eye or temple, associated with
the aura, the headache, and the postdrome head, with nausea and vomiting, intolerance watering red eyes and nasal congestion. The
(recovery stage). Symptoms of the prodrome of light and noise, and altered scalp sensation. pain is due to dilation (widening) of blood
include loss of appetite and changes in mood vessels, but the underlying cause is unknown,
About one-third of sufferers have migraine although temperature changes or drinking
INTENSITY Headache phase Course of with aura (classic migraine); migraine without alcohol may trigger an attack. Onset is rapid,
may last for migraine attack aura is called common migraine. There are and the headache is sometimes described as a
hours or days A typical migraine attack also various atypical migraine patterns, such red-hot poker in the eye. As the name suggests,
comprises four stages, as “ice pick” headache, “cold air” headache, the headaches occur in clusters. Attacks last
Postdrome which vary in intensity and “hat-band” headache, which tend to from a few minutes to a couple of hours and
phase and duration. recur in certain people. There is no cure, but recur up to several times a day. They may be
migraine can be controlled by avoiding triggers treated with medication or oxygen therapy.
TIME and by using drugs that help prevent or
limit attacks or relieve headache and nausea.

438

DISEASES AND DISORDERS

BRAIN AND SPINAL CORD DISORDERS

The brain and spinal cord process the information coming in from sensory nerves and
blood-borne chemicals and formulate responses that are sent to body tissues. Damage
to either of these structures can severely impair brain and body functions.

HEAD INJURY impact—the skull is a strong structure, and only covering the brain) or subdural (between Skull fracture
forceful injury will fracture it. The fracture may the brain and the tissues that cover it). The This three-dimensional CT scan
Many bumps and bruises to the head are expose brain tissue and the cerebrospinal fluid accumulating blood presses against the brain of the skull shows several severe
minor, but a severe blow or other injury (which cushions and protects the brain and and causes headache and altered consciousness. fractures. Injuries like these can
can put the brain tissue at risk of damage. spinal cord) to trauma and infection. A fracture cause brain damage or death.
at the base of the skull may allow cerebrospinal The brain may also be bruised in
Severe head injuries include open injuries, which fluid to leak down the nose or out of the ear. deceleration injuries (which occur when the Hematoma
expose brain tissue, and closed injuries, in which Where fluid can get out, infection can get body is moving fast and is suddenly halted, In this scan, the blue area
the brain is shaken inside the head. An open in. Shaking of the brain in the skull can cause as in a traffic accident). The shaken brain hits is a hematoma, or a pocket in
skull fracture may result from a heavy blow or bleeding, and the blood may build up to form a the inner surfaces of the skull, and is bruised which blood has accumulated,
hematoma. The hematoma may be extradural both at the site of the impact and then on outside the skull. Severe
(between the bone and the membranes the opposite side as the brain bounces back. bleeding within the brain
This results in concussion, which can cause is highlighted in orange.
Brain impact 2 Brain Brain impact 1 vomiting, double vision,
and headaches.
Movement
The brain may swell,
Brain Brain causing symptoms such
Skull as confusion, seizures,
loss of consciousness,
1 Moving rapidly 2 Impact and sometimes death.
In a person moving at speed—for example, in If movement is suddenly stopped, the brain Urgent treatment is
a car—the skull and brain are moving at the same hits the front of the skull, and then rebounds and needed to relieve the
speed as the body and the vehicle. hits the back (a “contrecoup” injury). pressure on the brain,
and to treat any bleeding.
Care and rehabilitation
may be needed for many
months afterward.

Arachnoid (site Choroid plexuses
of reabsorption) (site of production)

CEREBRAL PALSY HYDROCEPHALUS Third BRAIN AND SPINAL CORD
ventricle ABSCESSES
The name “cerebral palsy” is used for a This condition results from an excess of
group of disorders that result from brain cerebrospinal fluid, which puts pressure Fluid on the brain An abscess is a pus-filled swelling caused
damage and cause difficulties with on brain tissues and can damage them. Cerebrospinal fluid is produced by the choroid by infected material in body tissue; in the
posture and movement. plexuses that line the ventricles at the center of the brain or spinal cord, it can cause severe
Cerebrospinal fluid surrounds the brain and brain, and bathes the brain and spinal cord. Excess or life-threatening damage.
In many cases, the damage to the developing fills the ventricles (spaces) within it. Normally, fluid is reabsorbed via the arachnoid membrane.
brain occurs before birth; in others, the brain it cushions and nourishes the brain, and any Infected material can reach the brain or spinal
is starved of oxygen before, during, or just after excess is absorbed into the blood. Excess fluid cord directly if the blood-brain barrier is
birth. Cerebral palsy involves damage to the may build up due to overproduction, or to breached by injury, or from infections of the
motor cortex of the brain, leading to difficulties impairment of the drainage process by a sinuses (the bones around the ears and the eye
in standing and moving. If the disability is blockage or a structural abnormality. In babies, sockets) or the meninges. Abscesses of the
severe, there is spasticity (stiffness) of the arms the skull bones are not yet fused but are held brain or spinal cord are rare, but the symptoms
and legs. Mildly affected children may show together by stretchy cartilage. As the fluid are severe. In the brain, the pressure caused by
only slight stiffness and “scissoring” (crossing) gathers, the bones separate, causing the skull the abscess can result in confusion, headache,
of the legs and some alteration in their gait. to become large and translucent. fever, and possible collapse if the infection is
However, the cognitive (thinking) processes, severe. Abscesses around the spine may cause
and therefore the child’s intelligence, are not In adults, hydrocephalus causes increased pain and paralysis, and can swiftly lead to
necessarily affected. The child will need pressure on the brain, leading to persistent meningitis (see p.441) as the cerebrospinal
physical therapy, to keep the muscles flexible, headaches, which tend to be worse in the fluid carries infection to the meninges (the
and possibly help with speech and language. morning; problems with vision and gait; and tissues covering the brain). Surgery may be
The condition does not worsen over time, and drowsiness or lethargy. The excess fluid may needed to drain the abscess, and drugs will be
many children adapt well to their difficulties. be cleared with a shunt (drainage tube) which given to kill the infection and prevent seizures.
drains the fluid to another part of the body.

439

BRAIN AND SPINAL CORD DISORDERS

DEMENTIA EPILEPSY Site of seizure Secondarily
generalized

seizure

The name “dementia” refers to a gradual This disorder is typified by recurrent
loss of cognitive ability—understanding, seizures or convulsions as a result of
reasoning, and memory. abnormal electrical activity in the brain.

Dementia most commonly affects older NORMAL ALZHEIMER’S Brain cells send messages to each other, and
people. It is usually caused by diseases of the to the rest of the nervous system, in the form of
brain or the cerebral blood vessels. The most Brain activity electrical signals. Seizures occur when these Partial seizure
common form is Alzheimer’s disease, in which This PET scan shows the result of brain stimulation signals are temporarily disrupted. In epilepsy, Partial seizure
brain cells degenerate and deposits of protein tests made on a healthy person and a person with such abnormal brain activity is recurrent and The abnormal activity originates in one lobe
build up in the tissue. Another form is vascular Alzheimer’s disease. The blue areas show reduced unprovoked. It can arise spontaneously or result and remains confined to this area. In some
dementia, in which the small blood vessels brain activity in the person with the disease. from disease or damage to the brain. cases a partial seizure becomes generalized
supplying the brain are blocked by blood clots, and spreads (above right).
leading to multiple tiny areas of brain damage. symptoms do become worse and the person Seizures can be triggered by stress or a lack
Dementia with Lewy bodies is a condition in begins to forget basic information such as of food or sleep. Symptoms vary depending Site of seizure
which tiny round nodules, called Lewy bodies, where he or she lives. Problems such as on where the abnormal activity arises. Partial
collect in the brain and impair its function, speech difficulties, incontinence, and seizures involve only one side of the brain. Generalized seizure
causing symptoms such as hallucinations. personality changes may develop. Those with Simple partial seizures, confined to a small Abnormal activity spreads through the brain.
severe dementia may lose all memory of loved area, may just cause twitching of one body Symptoms vary but typically include uncontrolled
Dementia can occasionally occur in ones and friends and need full-time care. part, whereas complex partial seizures, in which movements of the whole body, with loss of
younger people, as a result of chronic brain the disturbance spreads to nearby areas, consciousness lasting from one to several minutes.
injuries, Parkinson’s disease, or Huntington’s To identify dementia, doctors may carry produce bizarre movements, confusion, and
disease. Most forms of dementia grow out scans and and assessments of mental loss of consciousness,
progressively worse over the years. Typically, abilities. The risk of dementia can be
the affected person’s relatives notice that he diminished by mental activity, especially new Generalized seizures, affecting the whole
or she has become more forgetful, with loss learning opportunities. Although there is no brain, cause loss of consciousness, collapse, and
of memory for recent events but with clear, cure, memory and daily life can be improved severe muscle spasms, followed by a period of
long-lasting memories about distant events. with mental exercises, and occasionally with altered consiousness and fatigue. Many sufferers
It is initially difficult to distinguish this from medication. experience a warning “aura” just before a
the normal aging process. Eventually, however, seizure, with abnormal sensations. Epilepsy can
be managed with medication to control seizures
and lifestyle changes to ensure safety.

Blood vessel Clot blocking
blood vessel

ELECTROENCELPHALOGRAPHY

Area of Vascular dementia Electroencephalography (EEG) is a recording EEG trace during generalized seizure
dead tissue In this form of dementia, tiny blood vessels of electrical activity within the brain. Small This EEG shows electrical activity across
throughout the brain become blocked, causing electrodes are fixed to the scalp with adhesive all areas of the brain, corresponding with
tissue death (infarction) in the areas that they gel and record brain activity for several a generalized epileptic seizure.
supply. The disease becomes worse as further hours. The results are shown as a trace
blood vessels are affected. on paper or a computer. EEG is often
performed on sleep-deprived patients, in
whom abnormalities are more likely to show.
During an epileptic seizure an EEG will show
areas of abnormal activity, and there may be
visible centers of abnormal activity even
when the person is not having a seizure.

BRAIN TUMORS is far less common. Malignant tumors typically separating them from the surrounding brain
grow fast and spread through the brain. Benign tissue would be too destructive, although
Tumors in the brain may be either benign tumors tend to grow more slowly and remain radiation therapy or chemotherapy can help
(noncancerous) or malignant (cancerous), in one area. Any kind of tumor can damage reduce their size. Many people with benign
but both types can cause severe the brain—there is no room in the skull for the tumors recover, but those with cancer may
impairment of brain function. tumor to grow, so it puts pressure on the brain face a shortened life expectancy.
tissue. Symptoms vary according to the area
Most brain tumors are metastatic, meaning affected; they include severe headaches, Site of tumor
that they grow from cancer cells that have confusion, blurred vision, paralysis of one body
spread via the blood from another part of the part, difficulty speaking or understanding Brain hemisphere
body. Breast and lung cancers are particularly speech, and changes in personality. If a tumor
liable to spread to the brain, and are often a causes bleeding, there may be sudden pain Meningioma
sign that the primary disease is accelerating. and loss of consciousness. It may be possible This scan shows a large tumor in the frontal lobes,
Primary brain cancer, originating in the brain, to remove a benign tumor surgically, although pushing the healthy brain tissue aside. The frontal
this epends on the site. Malignant tumors lobes affect personality, and changes in this area
generally cannot be removed because can lead to abnormal moods and behavior.

440

DISEASES AND DISORDERS

GENERAL NERVOUS SYSTEM DISORDERS

The nervous system carries a constant two-way flow of signals from body tissues to the brain and
responses returning from the brain to the body. However, certain disorders cause degeneration of
brain and nerve tissue, impeding or stopping these signals.

MULTIPLE SCLEROSIS an autoimmune disorder in which the immune PARKINSON’S DISEASE slower; and problems with balance. Abnormal
system attacks the body’s myelin tissue. The head movements are common, and the face
In multiple sclerosis (MS), nerves in the cause is unknown, although both genetic and This chronic, progressive disorder may become less expressive as the facial
brain and spinal cord suffer progressive environmental factors seem to play a part. typically causes tremor, slowing, stiffness, muscles lose their mobility. People may also
damage, which causes problems with and problems with voluntary movement. experience mood disturbance, depression,
a wide range of body functions. Typically, the disorder first appears between shuffling gait, problems with speech and
the ages of 20 and 40. Symptoms may include Parkinson’s disease results from degeneration cognition, and difficulties with sleep.
Electrical signals pass between the brain and problems with vision or speech, difficulties of cells in the basal ganglia, a part of the brain
the body along the nerves. Healthy nerves in with balance and coordination, numbness or involved in initiating movement. Normally, the Drugs may be given to mimic dopamine
the brain and spinal cord have a protective tingling, weakness, muscle spasms, muscle or cells produce a neurotransmitter (a chemical production, although over time these can
covering of a fatty substance called myelin, nerve pain, fatigue, incontinence, and altered that carries information between nerves) called become less effective. Treatment also includes
which enables signals to travel faster and more mood. In some people the symptoms come dopamine, which helps coordinate muscle physical therapy and lifestyle changes to help
smoothly. MS involves progressive destruction and go, although often with a deterioration activity. In Parkinson’s disease, these cells preserve mobility. Some people may be offered
of the myelin sheaths around the nerves. It is after each episode, while in others they grow produce much less dopamine, and the signals surgery such as deep brain stimulation, a
steadily worse. There is no cure, although to the muscles become slow and faulty. procedure in which electrodes are implanted
various drugs are used to relieve symptoms into the basal ganglia to help control tremors.
and delay the progression of the disease. The disease is most common in older
people, but may also occur in young adults or, Skull Fluid-filled ventricles
rarely, in children. In most people there is no (larger than normal)
obvious cause, although there is some evidence
T-lymphocyte Early stage for a genetic origin. Parkinson’s disease can also
T-lymphocytes and result from encephalitis, or from damage to the
Myelin sheath Nerve axon macrophages (cells basal ganglia by certain drugs or repeated head
from the immune trauma. The main symptoms are trembling of
Cell body system) attack the one hand, arm, or leg at rest, which may
myelin sheaths on progress to affect the limbs on the opposite
Damaged the nerves. Some side; muscle stiffness, which makes it difficult
myelin sheath repair may occur to begin moving and makes movements
in the early stages.
Demyelinated area Brain in Parkinson’s disease
Late stage This color-enhanced MRI scan of the brain in
Significant nerve injury Parkinson’s disease shows generalized shrinking
occurs early in MS. By (atrophy) of brain tissue. Other changes are
the late stage this has microscopic and cannot be seen on scans.
become irreversible,
with death of nerves
and scarring and
swelling of damaged
nervous tissue.

AMYOTROPHIC LATERAL susceptibility. Weakness first appears in the may become difficult, and the person may abilities are usually unimpaired. Most people
SCLEROSIS hands, arms, and legs. There may be muscle start to stumble. As ALS worsens, it causes with ALS die of respiratory failure only a few
cramps, twitching, or stiffness. Daily activities spasticity (severe muscle spasms), slurred years after diagnosis, although there are
such as holding objects and climbing stairs speech, and difficulty swallowing. Mental exceptions to this.

This incurable condition causes gradual Neurons (nerve cells) in the
but inevitable loss of function in the dorsal (back) horns receive sensory
motor nerves, which carry signals from information from around the body
the brain to cause conscious movements.
Neurons in the ventral (front) horns
Amyotrophic lateral sclerosis (ALS) typically Motor neurons in the spinal cord send motor nerve fibers to skeletal
begins between the ages of 50 and 70. The ALS destroys the motor nerves in the ventral muscles, causing them to contract
disorder damages both the nerves and the horns of the spinal cord. The most common form
muscles: as the motor nerves lose the ability to attacks here first, leading to peripheral weakness
stimulate muscle activity, the muscles weaken of the hands, feet, and mouth.
and waste away. The cause is unknown,
although in a few people there is a genetic

441

GENERAL NERVOUS SYSTEM DISORDERS/NERVOUS SYSTEM INFECTIONS

NERVOUS SYSTEM INFECTIONS

The brain and spinal cord are extremely well protected from infection, but any infective organisms
that do penetrate them can cause problems such as inflammation or tissue abnormalities, which
can become serious or even life-threatening.

MENINGITIS people with reduced immunity. Meningitis ENCEPHALITIS seizures, loss of consciousness, and coma.
may also result from certain drug reactions, or Difficulty speaking and paralysis in part of the
In this disorder, the meninges—the three from bleeding in the brain. In viral meningitis Inflammation of the brain, or body may also be present. The disorder is rare,
layers of membranes that surround the the symptoms arise gradually; in the bacterial encephalitis, is usually due to infection most often occurring in older people and children
brain and spinal cord—become inflamed, form they come on within hours. Inflammation but occasionally to autoimmune attack. It under 7. Encephalitis is usually diagnosed by
usually as a result of infection. may spread from the meninges to blood is a rare but life-threatening emergency. MRI scan and treated with drugs to kill infection.
vessels and brain tissue. Symptoms include Recovery may be slow and incomplete.
The most common forms in Western countries fever, headache with intolerance of light, stiff Most cases result from viruses, although bacteria Long-term consequences can include epilepsy,
are bacterial meningitis and viral meningitis. neck, vomiting, and altered consciousness. It and other microorganisms can also cause it. memory problems, and personality change.
The viral form (caused by organisms such as may be life-threatening and can cause brain The most common viral causes are herpes
enteroviruses) is more common but relatively damage. Vaccination provides protection; simplex (the cold sore virus), measles, and Infected tissue in
mild; bacterial meningitis (usually caused by meningitis requires urgent hospital treatment mumps; the incidence in children has greatly temporal lobe
Neisseria meningitides or Streptococcus where drugs may be given to kill the infection. reduced since vaccination became widespread.
pneumoniae) is much more serious. Other Encephalitis usually results from systemic Viral encephalitis
forms occur in the developing world or in Brain tissue (whole-body) infection breaching the brain’s MRI brain scan
defenses, but can also occur secondary to showing infected tissue
Meninges Dura mater meningitis (see left) or brain abscess (see p.438). due to encephalitis
The meninges comprise Arachnoid It causes flulike symptoms, fever, and headache; caused by herpes
the dura mater (outermost Pia mater more severe cases progress rapidly to confusion, simplex infection.
layer), arachnoid (middle),
and pia mater (inner layer)

Meningitis-causing bacteria Sites of infection HERPES ZOSTER as children, in pregnant women, and in people
The bacteria that most commonly give rise Most bacterial meningitis is caused by bacteria with a weakened immune system. After the
to meningitis are meningococci (shown here), transmitted through the bloodstream. Bacteria Also known as shingles, herpes zoster is a illness clears up, the virus lies dormant in the
Haemophilus, and pneumococci, although any can also enter the brain or spinal cord directly in nerve infection caused by a reactivation body but can be reactivated, causing shingles
bacteria could potentially cause the disease. head or spinal trauma, brain abscess, or surgery. of the virus that produces chickenpox. (an itchy, blistering rash, with burning or
stabbing pain, that follows the path of a nerve).
Chickenpox normally causes a blistering rash Herpes zoster may also result in inflammation
and mild illness, and lasts for about a week. and infection of various organs. In the brain, it
However, it can be more serious in adults and can cause loss of coordination, speech
older teenagers who did not have the disease disturbance, and encephalitis (see above), and
can be life-threatening. It may be treated with
antiviral drugs, steroids, and analgesics.

LUMBAR PUNCTURE The procedure CREUTZFELDT-JAKOB A rare variant form is inherited. The prion
The person lies on one side, curled DISEASE protein triggers a misfolding of normal proteins
In this procedure, a sample of cerebrospinal up as tightly as possible, and the needle in the brain. As a result, the brain cells die and
fluid (the fluid that bathes the brain and is inserted between two of the lumbar This is a rare brain disease, similar to BSE are replaced with
spinal cord) is taken from the spine with a vertebrae into the subarachnoid space (mad cow disease) in cattle and scrapie in deposits of prions.
needle. Lumbar puncture is used mainly for below the bottom of the spinal cord. sheep, that may be contracted by eating This causes rapid loss
diagnosing meningitis, by identifying contaminated meat or may be inherited. of body functions,
the organisms causing the infection and Cerebrospinal Spinal dementia, progressive
revealing high numbers of white blood cells fluid cord Creutzfeld-Jakob disease (CJD) is thought to brain failure, and
(which fight infection). It may also be used be caused by prions, abnormal proteins that death within months.
to detect abnormal protein and antibody Spine behave as infectious organisms and have a
levels if multiple sclerosis is suspected, or particular affinity for nervous tissue. The new Brain with CJD
to detect bleeding or a tumor in the brain. Hollow needle variant form of CJD, first diagnosed in 1996, In this MRI scan, the
Lumbar puncture is occasionally used to is acquired from prion-contaminated meat. red areas show the
remove excess cerebrospinal fluid if it is Similar conditions are seen in some animals. thalamus, in which the
putting too much pressure on the brain. tissue has degenerated
as a result of vCJD.

442

DISEASES AND DISORDERS

MENTAL HEALTH DISORDERS

Disorders of the mind may involve mood, as in depression; thought, as in OCD; or SUBSTANCE ABUSE
serious disturbance of brain function. Talking therapies and medications can help
managing symptoms, but the more serious relapsing illnesses cannot be cured. The main substances of abuse are alcohol;
tobacco; and illegal or restricted-use drugs
DEPRESSION poor sleep, and poor appetite. In Prefrontal such as heroin, amphetamines, cocaine,
severe cases, an affected person cortex cannabis, benzodiazepines, and LSD. Drugs
This is broadly speaking a condition of may consider or attempt act on the brain’s “reward system,” which
depressed mood and feelings of sadness, suicide, or may develop Hippocampus normally responds to pleasurable stimuli,
but it affects people in different ways. psychosis (delusional Amygdala making us want to repeat the activity.
thoughts). It is a chronic Taking a drug overstimulates this system,
Depression causes lowered mood, drive, and condition, typically producing a “high” feeling. The brain can
enjoyment, leading to a sense of sadness and lasting for several become dependent on the drug and
hopelessness. It is very common, but is often months unless treated, may experience unpleasant withdrawal
not diagnosed and treated. Depression is also and recurring in most symptoms if the drug is stopped. The same
more than just temporary sadness—it is a people. Treatment may drugs can also cause mental problems
medical condition caused by disorders in involve talking therapies, such as such as paranoia and psychosis.
brain chemistry that can seriously disrupt cognitive behavioral therapy or
daily life. Those affected see the whole world, psychotherapy, antidepressant medication,
including themselves, as pointless and useless. or electroconvulsant therapy.
Some people become flat and down, lacking
energy, with excessive eating and sleeping. Brain areas and mood
Others become more anxious, with agitation, Mood and feelings are regulated by three
main areas. The amygdala and the hippocampus
produce emotional responses, and the prefrontal
cortex generates thoughts about those emotions.

ANXIETY DISORDERS which would have saved our distant ancestors heartburn. It also causes feelings of being on OBSESSIVE COMPULSIVE
from the many physical dangers that they edge, anger, sleeplessness, poor concentration, DISORDER
Anxiety is a condition that causes fear, faced. This primitive but vital response still and difficulty coping with simple stresses
agitation, worrying, poor sleep, loss operates in the modern world but is triggered without feeling overwhelmed. At its worst, The main characteristics of this disorder
of appetite, and physical symptoms. by stresses such as problems at work or in anxiety can lead to panic attacks, with shaking, are repetitive behavior and intrusive
personal relationships. Some people have a sweating, racing heartbeat, and a feeling that thoughts that can interfere with daily life.
Anxiety is a natural response to stresses, which stronger than usual response to stresses, which one is about to die.
arises in the amygdala and hippocampus—in they may have inherited. Otherwise, anxiety Many people have some degree of obsessive
evolutionary terms, the oldest parts of the can arise as a result of difficult life events such Treatment may involve learning relaxation or compulsive tendencies. However, in
brain. It stimulates the fight/flight response, as loss of a job. Chronic anxiety produces techniques or undergoing a “talk treatment” obsessive compulsive disorder (OCD), the
physical symptoms such as fast heart rate, such as cognitive behavioral therapy to help need to perform a specific action becomes
NORMAL MANIA sweating, butterflies in the stomach, and control thought patterns that can lead to stress. constant, and the person may become very
Antidepressant drugs may also be given. anxious if unable to carry out the action. The
Brain activity scan BIPOLAR DISORDER person may also have intrusive or upsetting
During a high or manic phase of bipolar disorder thoughts; and delusional beliefs that can thoughts, such as fear that their loved ones will
the brain shows increased levels of activity as This condition causes extreme mood render the person a danger to themselves or die if they do not carry out the action. Many
shown in this brain scan. Common symptoms swings, with alternating periods of others. At worst, mania leads to psychosis, can be helped with antianxiety medications
include increased energy and less need for sleep. profound elevation in mood (hypomania disordered perception, or hallucinations. By and therapies that help people confront and
and mania) and depression. contrast, in the depressive phase, the person manage the fear underlying their behavior.
loses all interest in life and hope for the future,
Bipolar disorder, also called manic depression and may be low enough to consider suicide. Compulsive
or manic affective disorder, causes episodes handwashing
of high or euphoric mood, alternating with Most affected people have longer periods A common “ritual”
depression. During a “high” phase, known as of depression and relatively short periods of action seen in OCD is
mania, the person can feel elated, confident, mania, interspersed with periods of normal compulsive washing of
full of energy, and highly creative. However, mood, and the condition is chronic and hands, due to extreme
the elevated mood can lead to risky behavior recurrent over many years. Treatment is with fear of contact with
such as overspending or unsafe sex; sometimes long-term medication to correct the disorders dirt or germs.
feelings of being indestructible; disordered in brain chemistry and thereby stabilize the
moods, together with intensive psychological
support through high or low periods. If the
symptoms are particularly severe, the person
may need treatment in the hospital.

443

MENTAL HEALTH DISORDERS

SCHIZOPHRENIA about them. A person may also have delusions, Frontal lobe
such as believing that people on television
Schizophrenia is characterized by a loss are speaking directly to them, as well as Temporal lobe
of contact with reality with hallucinations difficulty distinguishing reality. Other
and delusions. symptoms include disordered thinking Hippocampus
and bizarre repetitive movements.
Schizophrenia involves a mixture of “positive” Schizophrenia and the brain
symptoms such as hallucinations, which tend Negative symptoms include loss of Studies have shown an excess of some
to predominate early in the course of the emotional expressiveness and social neurotransmitters in some parts of the
condition, and “negative” symptoms such as withdrawal. Schizophrenia has some genetic brain of those with schizophrenia, but
lack of any pleasure in life, which predominate basis, and tends to appear in the late teens or it is not known if this is a cause or a
later as the positive symptoms die down. early 20s. Stressful life events may trigger the result of the condition.
Hallucinations most commonly involve an onset or cause flare-ups. The condition needs
affected person hearing voices talking to or long-term treatment with antipsychotic
medication, social support, psychotherapy,
and rehabilitation, but rates of physical illness,
anxiety, and depression are high.

EATING DISORDERS periods of fasting with intense binges Dry, brittle Dizziness; depression;
of overeating, often of high-calorie hair; hair loss low self-esteem
Psychological disorders to do with eating “forbidden” foods, followed by
cause the affected person to avoid food, self-induced vomiting, sometimes Fatigue; fainting; Gum disease; sensitive
induce vomiting, or, conversely, to with laxative abuse. People with depression; moodiness teeth; tooth erosion
overeat compulsively. bulimia may have normal body and decay
weight, but they are at risk of salt Dry skin; growth of
Anorexia nervosa and bulimia nervosa are the imbalance, tooth decay, and downy hair on body Sore throat;
most common eating disorders; many affected stomach rupture. inflammation
people have elements of both. People with Low blood pressure; of esophagus
anorexia believe themselves to be fat when Other disorders include palpitations
they are very underweight. The disorder begins compulsive overeating and Low blood
with severe calorie restriction but may progress eating non-food items such as Muscle weakness; pressure; heart
to refusal of all food and fluids. Menstrual paper tissues. Eating disorders bone thinning muscle disorders
periods may stop, and fine, downy hair may may be brought on by stress
grow on the body. Anorexia has a 10 percent and a need for control in life, Kidney stones Stomach pain;
fatality rate. Bulimia involves some of the same but the illness can come to and failure bloating;
attitudes to the self, but people alternate short take over a person’s life. ulceration
Treatment involves Bloating and
psychological help and constipation Anemia; low
nutritional support. levels of
electrolytes;
dehydration

Anemia; low levels
of electrolytes

Acid-worn teeth in bulimia Cessation of Irregular or
Recurrent vomiting in bulimia causes the teeth to menstruation in absent periods
be exposed repeatedly to gastric acid. This wears women; problems
away the enamel covering the teeth; eventually Effects on body in conceiving
the enamel is worn through and the teeth decay. Anorexia and bulimia both have
widespread effects on the body, Muscle
affecting almost every system. weakness

ANOREXIA NERVOSA BULIMIA NERVOSA

PERSONALITY DISORDERS or others. The disorders fall into three main PHOBIAS with daily life. Many people manage phobias
groups. The first group (paranoid, schizoid, effectively by avoidance. However, some, such
These disorders involve persistent, fixed schizotypal) involves odd or eccentric thinking. A phobia is an intense and persistent fear as agoraphobia (a fear of going out), can
dysfunctions in a person’s perceptions The second (histrionic, borderline, narcissistic, of certain objects, people, animals, or become disabling, and challenging them can
and the way they relate to others. antisocial) is typified by emotional, impulsive, situations, so that the person feels great provoke severe anxiety. Phobias can be cured
attention-seeking, or cruel behavior. The third anxiety if forced to confront them. by very gradual phased exposure to the source
Our personality is largely established by the (avoidant, dependent, obsessive-compulsive) of their fear, sometimes aided by sedating
time we reach adulthood. In most people, shows anxious or fearful thinking. Personality Some fears, such as fear of deadly creatures medication. Alternatively, people may be given
it continues to develop in response to new disorders cannot be cured, but management or fear of heights, are normal, natural survival “flooding therapy,” when massive, sustained
experiences. However, people with personality involves talking therapies such as cognitive mechanisms. Phobias, however, are fears that exposure is used to demonstrate that the
disorders show rigid, dysfunctional patterns of behavioral therapy (CBT), as well as support to involve nondangerous animals, objects, or feared object or situation is harmless. A third
behavior that cause problems for themselves help the person gain insight into the way they situations, or are so intense that they interfere method is “counter-conditioning,” in which the
respond to the world and to help them adapt affected person learns relaxation techniques
their behavior and function successfully. to replace the fear response.

444

DISEASES AND DISORDERS

EAR DISORDERS

The ear is a complex structure whose roles include converting sound waves of differing
amplitude and frequency into nerve impulses for transmission to the auditory cortex,
localization of sound, and the sense of balance and body position.

OUTER EAR DISORDERS middle ear. It can be extremely painful, but can MIDDLE EAR INFECTIONS
usually be relieved by ear drops. People with
The outer ear comprises the pinna or recurrent infection may find that nightly The ear drum and the space behind it are
visible part, and the ear canal, leading to application of olive oil will protect the ear highly sensitive structures, so infections
the ear drum. Problems here can cause canal and reduce the frequency of attacks. in this area can be extremely painful.
discomfort but are usually treatable.
Infected ear canal The middle ear space, which lies behind the ear
The ear canal secretes ear wax to clean and Ear canal infection is prone to cause discharge, drum, contains three small bones (ear ossicles);
lubricate the canal. Most excess wax comes usually due to a mixture of pale yellow fluid from these bones transmit vibrations from the ear
out by itself. Any build-up can be cleared by the inflamed tissues and wax liquefied by the drum to an inner window connecting with the
warm olive oil or ear drops, to melt the wax increase in temperature as a result of infection. hearing nerves, which turn the vibrations into
and relieve the sensation of blockage. Using electrical signals that pass to the brain. Normally
objects such as cotton buds to clean the ear, this space is filled with air, which enters through Ear infection
however, interrupts the outward flow of wax, the Eustachian tubes. Middle ear infections may When the ear is infected the normally
compressing it back against the ear drum and arise during an infection such as a cold, when translucent ear drum looks dull and may
damaging the skin of the ear canal. Infection of mucus builds up in the middle ear and air can bulge under pressure.
the ear canal can occur when the delicate no longer get in. The trapped mucus thickens
lining of the ear canal is damaged, most often and becomes infected with viruses and, in some the mucus drain out. Ear infections are more
by having objects poked into it, irritation from cases, bacteria. This causes pain and reduced common in children under 6, who have shorter,
detergents such as shampoo and chlorinated hearing. Sometimes the mucus exerts so much straighter Eustachian tubes than adults, allowing
water, or infection spreading out from the pressure on the ear drum that it bursts and lets bacteria swift passage to the middle ear.

PERFORATED EAR DRUM CHRONIC OTITIS MEDIA may be fitted into the ear drum to allow air LABYRINTHITIS
WITH EFFUSION into the middle ear. They do not prevent ear
The ear drum, or tympanic membrane, infections, but do help clear mucus and This common condition of dizziness and
sits between the ear canal and the middle Common in children, otits media is due to improve hearing. The condition is most nausea is caused by inflammation in the
ear. Its job is both to amplify sound and the accumulation of mucus in the middle common in children under 5 years, who have inner ear. It is painless but often very
to protect the middle ear from debris. ear cavity, which normally contains air. short, straight tubes, which are more susceptible unpleasant in its effects.
to viral infections from the throat. As the adult
External or middle ear infections can cause the In adults, the condition is commonly due to teeth come through, the jaw lengthens and the The labyrinth is a coiled, fluid-filled structure in
ear drum to become inflamed. Pressure from long-term Eustachian tube blockage (often tubes lengthen and become less straight. the inner ear that consists of the cochlea (the
fluid in the middle ear can make the ear drum associated with sinus problems). The Eustachian hearing apparatus) and the vestibular system
burst; when it does so the ear may discharge tubes connect the middle ear space to the back Ear tube (the balance apparatus). The role of the
a bloody fluid, although pain is often partly of the throat, keeping the space ventilated and vestibular system is to sense the position of the
relieved. The drum can also be perforated by at the correct pressure. If the tubes are blocked, Chronic otitis media with effusion head in relation to gravity, indicating whether
objects being used to clean the ear canal. air cannot get into the middle ear. Gluey mucus An ear tube has been inserted into the drum to the head is upright or tilted, and to help the
replaces it and remains trapped there, reducing allow air into the middle ear space, preventing eyes stay focused on objects as the head is
Most perforated drums heal by themselves the ability of the ossicles (tiny bones in the development of chronic otitis media. The turned. Inflammation of the labyrinth upsets
over a couple of weeks; the ear canal and middle ear) to transmit sound. Hearing is condition is caused by bacteria or viruses. the balance system, causing vertigo, nausea,
drum must be kept dry while they recover. reduced, and the ear feels full. A popping and disorientation. If both labyrinths are
If the ear drum does not heal, it may need sound can occur when the Eustachian tubes involved, these symptoms can be severe.
surgical repair. intermittently open to let a little air in.
The brain can compensate for the
View of perforated In children, the condition commonly follows disturbances to the inner ear, but loud sounds
ear drum ear infection, when the mucus can be slow to and sudden head movements stimulate the
The eardrum has burst, clear. If the child has several ear infections in a labyrinth and make symptoms worse. Viral
allowing trapped pus row, the mucus can become persistent, leading labyrinthitis is the most common type, and can
to escape. to prolonged hearing reduction that can affect last from several days to several weeks. Bacterial
schooling or language development. When this labyrinthitis is less common but, if untreated,
happens, a small ventilation tube, or ear tube, can lead to permanent impairment of hearing.

445

EAR DISORDERS

ADULT HEARING LOSS and is usually temporary. It can be resolved by TINNITUS pulsating blood vessels in the ear, or false
syringing the ear. In children it may be caused signals from damaged nerves. Causes of
Some degree of hearing loss is common by chronic otitis media with effusion (see left). Damage to the hearing apparatus can temporary tinnitus include ear wax, glue ear,
as part of the aging process, but hearing Sensorineural hearing loss most commonly cause tinnitus, the perception of sound ear infection, and exposure to noise. Permanent
can also be damaged by loud noise, occurs during the aging process as the cochlea when no external sound is present. tinnitus is usually caused by damage to the
injury, or disease. deteriorates. This is known as presbyacusis, and auditory (hearing) nerves, including age-related
it affects many people over the age of 50. The sounds associated with tinnitus range from loss (in these cases, the frequency of the sound
Hearing loss may be conductive (due to poor intermittent and quiet to a constant loud noise, is often in the range that the person can no
sound wave transmission) or sensorineural Persistent exposure to loud noise can and one or both ears may be affected. They longer otherwise hear). The condition can be
(due to nerve damage). Conductive hearing also cause sensorineural hearing loss as this include whooshing, hissing, musical sounds, difficult to tolerate, as people with the condition
loss is often caused by a blockage of earwax damages the nerves more rapidly. Ménière’s clickings, and buzzings. The origin can be the have to develop strategies to ignore or mask
disease (see right) or damage to the cochlea the sound. It can be cured by cutting the
may also cause sensorineural hearing loss. auditory nerves, but absolute deafness results.
The ability to hear high-frequency (high-
pitched) sounds is reduced first, and the MENIERE’S DISEASE both ears. The underlying cause is a problem
problem may initially be noticed when the with the drainage of the fluid in the vestibular
This inner ear disorder is common but system (the balance apparatus). This causes an
frequencies of speech become difficult to long-lasting and difficult to treat well and increase in fluid pressure, resulting in damage
distinguish. Tests can be done to find the its symptoms can be disabling. to the sensitive nerve structures. It usually
cause and seriousness of the problem. comes on gradually, but sudden attacks of
Hearing aids (see below) may help Ménière’s disease is a disorder of the fluid in severe vertigo, lasting less than 24 hours, are
people to cope with loss of hearing. the labyrinth, which contains the organs of common and can cause people to fall to the
hearing and balance. It typically causes tinnitus ground. The underlying trigger is unknown,
Auditory nerve although the viral infection herpes has been
(see above), hearing loss, vertigo (see suggested. The vertigo and tinnitus can be
Cochlea below), and a full feeling in the cured by cutting the auditory nerves, which
ear, and may affect one or causes total deafness, so most sufferers choose
Eustachian tube to manage the symptoms instead.

Outer ear Bones of Semicircular
canal middle ear canals

Structure of the ear LOCATION Semicircular
Hearing is affected by problems in various canals
structures of the ear, which may result in
partial or complete hearing loss. Most Vestibular Vestibular
adult hearing loss is age-related. nerve nerve

Tumor

HEARING AID Tumor in left internal auditory canal Balance mechanism Utricle Saccule Ménière’s disease Dilated Dilated
This acoustic neuroma (tumor) is growing on Contained within a bony Vestibule A buildup of excess fluid utricle saccule
The purpose of a hearing aid is to amplify the cochlear nerve. These tumors are benign labyrinth are the fluid- in the vestibule causes
(increase) the sound reaching the inner ear. but cause progressive hearing loss, with vertigo filled organs of balance; the chambers to dilate Dilated vestibule
The device is an electroacoustic amplifier, and tinnitus, and usually require surgery. the semicircular canals and then, it is thought,
consisting of a microphone, amplifier, and and the vestibule. Fluid to rupture.
speaker. The limitation of hearing aids Wearing hearing aids movement is interpreted
is that they only amplify sound, but do not Hearing aids are usually worn inside or behind by the brain as motion. from an inner ear disorder, as in benign
clarify it—and much hearing loss involves one or both ears. Some have an in-canal paroxysmal positional vertigo (BPPV), which is
high-frequency sounds such as consonants. receiver with an amplifier behind the ear, VERTIGO caused by tiny crystals in the balance system
The result can be that speech is less clear while others are surgically implanted. being displaced. It can also be caused by poor
rather than not loud enough. To combat blood supply to the balance system (often due
this problem, FM listening devices are being An unsteady feeling due to upset balance, to atherosclerosis), Ménière’s disease, or ear
developed with wireless receivers integrated vertigo can be brought on by visual infection. In addition, vertigo can result from
with hearing aids. stimuli or by being spun around, or can problems in the balance centres of the brain;
be a symptom of a balance disorder. for example, due to migraine or stroke. It is
usually worsened by sudden head movements
Vertigo gives a sensation of spinning or tilting, and loud noises, and partially relieved by drugs
sometimes with nausea or vomiting. In some to relieve nausea or simply closing the eyes.
people it is triggered by heights. It can result

446

DISEASES AND DISORDERS

EYE DISORDERS

The eye collects light by focusing, then converts the light signals into sequences of nerve messages
that enable the brain to build an accurate picture of the world, in full color. Disorders can affect all
parts of this surprisingly tough structure.

EYELID DISORDERS INFLAMMATION OF THE contact with the eye surface. Many chemicals Conjunctivitis
EYE SURFACE can irritate the eye, such as chlorine, used in Conjunctival inflammation is common and causes
The eyelids can be affected by irritation swimming pools, and pyruvic acid, released a sore, itchy, red eye, often with sticky or crusty
or infections on their surfaces, at the The conjunctiva is a sensitive layer of cells when cutting onions. Allergic conjunctivitis is discharge, but without any real impairment of
margins, or in their internal structures. covering the sclera (the white of the eye), often caused by pollens, in which case it is vision or focusing ability.
inner eyelids, and cornea, and can suffer seasonal (hay fever), but may occur throughout
The eyelids protect the eye surface, both directly damage for a variety of reasons. the year if it results from other forms of allergy. LENS PROBLEMS
and by spreading tears and lubricating fluid
across it. The most common disorders affecting Infective conjunctivitis may be caused by Atmospheric irritation such as wind, heat, The most common disorder of the lens
them are inflammation at the margins, known bacteria (usually staphylococci) or by viruses solar radiation, ultraviolet light, and dust may is cataract, in which the lens becomes
as blepharitis, styes, and chalazia. (often adenoviruses). People who wear contact cause progressive damage to the cornea, leading clouded and cannot focus light properly.
lenses are particularly vulnerable. Chemical to thickening and degeneration. These changes
Blepharitis results from infection of the conjunctivitis results from irritants coming into may result in pinguecula, an area of yellowish The lens is a clear, rounded structure suspended
follicles at the roots of eyelashes, usually by thickening, or pterygium, a lumpy growth on between the front and rear chambers of the eye,
staphylococci (the bacteria that commonly GLAUCOMA the surface of the eye. Surgery may be needed and changes its shape to focus light precisely
cause conjunctivitis) or fungi (often associated if these areas spread across the cornea. on the retina. A cataract is a clouding of the lens
with seborrheic dermatitis, a type of eczema). A common cause of visual loss, glaucoma from clear to milky-white. Symptoms include
It causes a gritty, irritated feeling, but can be often runs in families and generally with increased pressure in the eye do not go blurred or distorted vision and “dazzle” around
relieved by cleaning the eyelids, ideally with becomes more common with age. on to develop the condition. Glaucoma may lights, and, if untreated, blindness. Cataracts
diluted baby shampoo, and warming the eyelid be chronic (long-term) or acute (short- lived). may be caused by eye trauma, drugs (such as
margin to melt and release trapped sebum. Normally, fluid is secreted into the front of the Chronic glaucoma is painless and can go long-term corticosteroid use), overexposure to
eyeball by a structure called the ciliary body, to unnoticed for years. Increased pressure within environmental irritants such as ultraviolet light
Rosacea, a skin inflammation common in nourish the tissues and maintain the shape of the eye reduces the blood supply to the optic and solar radiation, or changes due to aging.
older women, may cause blockage of the eyelid the eye. Excess fluid drains away through a gap and retinal nerves, causing progressive damage Most cataracts are treated by surgery, which
glands, producing a similar result. Styes and called the drainage angle. In glaucoma, the to these nerves and areas of visual loss. consists of breaking up and removing the center
chalazia are infected glands in the eyelid, which system that allows this movement of fluid part of the lens and replacing it with a plastic
cause red, painful lumps. Styes develop in the becomes blocked, and fluid builds up in the In acute glaucoma, the pressure in the eye lens, to allow restoration of useful vision.
sebaceous glands at the edge of the eyelids. eye. Raised pressure in the eyes is a common rises quickly, because the iris bulges forward
Chalazia develop in Meibomian glands (tiny risk factor for glaucoma; however, most people and blocks the drainage angle. It causes Cataract (cloudy lens)
glands that secrete oily fluid to lubricate the severe pain and sudden loss of vision, and A cataract may affect just one eye, or both eyes
eye) and are bigger and farther from the edge is a medical emergency, but a small surgical may be affected, one more severely than the
than styes. Both disorders usually get better procedure will relieve it. Acute glaucoma is other. Here, the right eye has a dense cataract,
with the application of warm compresses. more common in farsighted people because making the entire pupil appear opaque.
Good eyelid care, careful removal of eye the eyeball is smaller and more prone to
makeup, and regularly replacing mascara, if structural and functional problems.
used, may help prevent all of these conditions.
Blocked
Stye on eyelid trabecular
A familiar eyelid disorder, a stye causes pain when meshwork
blinking, and is sometimes accompanied by a a
discharge. Styes are more common in people with Ciliary muscle
seborrheic dermatitis, a type of eczema.
LOCATION Drainage angle

Trapped fluid

Chronic glaucoma Iris
Usually fluid continually

flows out through the

pupil and drains out of Cornea

the trabecular meshwork,

a sievelike structure Lens
located between the iris

and the edge of the cornea.

In chronic glaucoma, the

meshwork becomes

blocked and pressure

builds up in the eye.

447

EYE DISORDERS

FOCUSING PROBLEMS the lens is responsible for accommodation, glasses or contact lenses. This condition in front of the retina because the eyeball
or adjustment of focus between near and far is called presbyobia. It differs from near- is too long, the cornea too curved, or the
The most common disorders of vision are objects. This is achieved by the ciliary body, and farsightedness, which affect all aspects lens too powerful for the length of the eye.
refractive (focusing) errors and can often a ring of muscle that contracts to make the of vision. In farsightedness (hypermetropia)
be corrected by wearing glasses. lens rounder, or relaxes to make it flatter. either the eyeball is too short, the lens not The degree of myopia is measured by the
round enough, or the cornea not curved strength of the spectacle lens needed to correct
The lens is the main structure involved in The ability of the lens to change shape enough. As a result, light rays are not focused it. In very high myopia there is an increased
focusing light, although the cornea and the declines with age, partly due to age-related exactly onto the retina, but the “focus point” risk of retinal detachment. Astigmatism, in which
fluid in the eye also play a part. In particular, stiffening of the lens and partly due to would actually lie behind the eye, so vision there are irregularities in the shape of the lens
lessening in the power of the ciliary muscles. is blurred. In nearsightedness (myopia), or the cornea, also impairs focus. These
By the age of 60 most people cannot achieve the opposite occurs: the light rays converge problems can usually be corrected by glasses
near focus (used for reading) without wearing or contact lenses or through laser eye surgery.

Retina Cornea Retina Cornea LASER TREATMENT

Light rays Light rays This procedure is designed to correct
focus converge nearsightedness, farsightedness, and
too soon astigmatism. It involves the use of lasers to
behind reshape the cornea, aiming to eliminate
retina the need for glasses. Laser correction has
not previously eliminated the need for
Lens Light rays Lens Light rays reading glasses, since age-related loss of
UNCORRECTED NEARSIGHTEDNESS accommodation is not related to lens and
corneal curvature. However, new advances
mean that this is also becoming possible.

UNCORRECTED FARSIGHTEDNESS

Retina Convex Retina Concave
lens makes lens makes
Light Light ray
focuses light rays focuses on light rays
on retina converge bend apart
retina

Lens Lens of eye Laser eye treatment
CORRECTED FARSIGHTEDNESS CORRECTED NEARSIGHTEDNESS This form of surgery involves opening a flap
in the corneal surface and removing some of
Farsightedness Nearsightedness the tissue from inside, or removing some of
The eyeball is too short relative to the focusing power of the The eyeball is too long relative to the focusing power of the lens, the outer layer, to make the cornea flatter.
cornea and lens, so light is focused behind the retina. A convex so light is focused in front of the retina. A concave lens makes the
lens bends the light rays together so that they meet on the retina. light rays diverge (bend apart) so that they meet on the retina.

UVEITIS AND IRITIS DISORDERS OF THE RETINA bleeding from ruptured blood vessel linings. a common cause of blindness and results from
This condition, often termed retinopathy, degenerative change in the retina around the
These terms describe inflammation of a The retina is a delicate, light-sensitive is most common in diabetes mellitus and macula (the central point of vision). The retina
group of structures in the eye (the uvea) structure lining the back of the eye. It can hypertension (high blood pressure). can also become detached from the back
and the iris, the colored part of the eye. become damaged through a variety of of the eye and its blood supply, for example
disorders and injuries. Chronic glaucoma may also damage the by injury, so that loss of vision results.
Both uveitis and iritis cause pain and reduction retina through compression of the surface Reattachment by laser, if done within
in vision. There are many possible causes; the The retina receives an image of the world from blood vessels, which leads to restriction of a few hours, may successfully restore vision.
most common are inflammatory disorders, the focusing structures of the eye and converts the blood supply. Macular degeneration is
such as Crohn’s disease, and infection, this into nerve messages that are sent to the
particularly by herpes viruses, including brain. It contains light-sensitive cells, as well as Normal retina Leaking blood vessels
shingles. Inflammatory joint conditions such a network of blood vessels that supplies it with
as rheumatoid arthritis can also affect the eye. nutrients. Depending on the area of the retina Retinopathy
Symptoms include redness, blurring of vision, affected, any problem has the potential to Magnified retina of a
and aching in the eye. Iritis and uveitis can impair vision. Permanent damage results in healthy eye (left) and
permanently impair the vision, causing scarring loss of vision in the corresponding area of the an eye affected by
and sticking of the eye structures, and require visual field. One possible cause of damage is diabetes (right), a
treatment by an ophthalmologist. impaired blood flow, including blockages and common cause of
retinopathy. The leaking
blood vessels and
blockages are evident
in the affected eye.

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DISEASES AND DISORDERS

RESPIRATORY DISORDERS

The upper respiratory tract constantly encounters inhaled microbes and often becomes infected. The lower
respiratory tract can become irritated and damaged by inhaled agents, especially cigarette smoke—the
major cause of lung cancer and chronic obstructive pulmonary disease.

COLDS AND INFLUENZA RHINITIS AND SINUSITIS forward, a discharge of pus from the nose, Location of sinuses
and fever. Treatment is with analgesics and There are four pairs of sinuses, which drain
Viral upper respiratory tract infections Inflammation of the sinuses and the decongestants. Antibiotics may be used in through small channels. These channels may
are most common in winter. The common linings of the nasal cavity may occur bacterial or chronic sinusitis. Chronic sinusitis become blocked when inflamed, leading to a
cold is mild and short-lived but influenza together and be acute or chronic. They may sometimes require surgery. buildup of fluid and a sensation of pressure.
can lead to serious complications. are due to infection or other causes.
Sphenoid sinus
The viruses that cause colds and influenza are Rhinitis causes a runny nose, sneezing, and
airborne, spreading in fluid droplets coughed nasal congestion. It may be allergic (see p.460), Frontal Ethmoid
or sneezed out or in films of moisture transferred infectious (such as a cold), or vasomotor. In sinus sinuses
to close contacts by sharing objects or shaking vasomotor rhinitis, blood vessels in the nose
hands. Most adults develop the common cold are oversensitive and overreact to changes in Frontal
up to four times a year, children more often. It weather, emotion, alcohol, spicy foods, and sinus
is caused by over 200 different viruses, and, as inhaled irritants such as pollution. It is treated
yet, there is no vaccine. It starts with sneezing by avoiding triggers and using nasal sprays. Ethmoid
and a runny nose with mucus (initially clear, sinuses
then thicker and darker), then a headache and Sinusitis may be acute—clearing up within
mild fever may develop along with a sore 12 weeks, or chronic, lasting for over 12 weeks. Sphenoid
throat, cough, and sore, reddened eyes. It is Acute sinusitis is most common and typically sinus
relieved by regular intake of fluids and rest. follows a cold. Symptoms include headache,
facial pain, facial pressure when bending Maxillary
Influenza is caused by three main types sinus
of influenza virus called A, B, and C, and is
common. A new vaccine is developed annually Maxillary
to fight the most common strains, and yearly sinus
vaccination is important, particularly for those
at risk of complications, people over 65 or FRONT VIEW SIDE VIEW
under 5 years, and those with other health
issues. Symptoms include a high fever, muscle THROAT DISORDERS viral. Symptoms include a sore throat, pain Tonsillitis
aches and pains, coughing, sneezing, sweats, and difficulty in swallowing, fever, chills, and The tonsils are swollen and have white, pus-filled
shivers, and exhaustion. It typically lasts a Inflammation in the tonsils or pharynx enlarged lymph nodes in the throat. Treatment spots on them. For recurrent episodes or when
week, but fatigue may persist. Complications (throat) leads to a sore throat; in the is with rest, fluids, analgesics, and lozenges and swallowing becomes impossible, surgical removal
include pneumonia, bronchitis, meningitis, and larynx, to hoarseness; and in the sprays. Antibiotics may also be given. of the tonsils (tonsillectomy) may be performed.
encephalitis. Treatment includes intake of epiglottis, to blockage of the airway.
fluids, rest, and antiviral medications. Bacterial infection of the epiglottis
The pharynx connects the back of the mouth (epiglottitis) usually affects children. It causes
and nose to the larynx (voice box) and the fever, drooling, hoarseness, and stridor (an
esophagus. Infection of the tonsils (tonsillitis) abnormal, high-pitched breathing noise). This
or pharynx (pharyngitis) can be bacterial or condition requires urgent medical attention.

Pharynx Tonsils Inflammation of the larynx (laryngitis) can
be due to infection, overuse of the vocal cords,
gastroesophageal reflux disease, or excessive
smoking, alcohol, or coughing. Laryngitis
causes hoarseness or inability to speak. When
due to infection, there may be fever and flu or
cold symptoms. Chronic laryngitis is treated by
addressing the underlying cause, resting the
voice, and voice therapy. Chronic laryngitis can
cause white plaques (leukoplakia) to develop
on the vocal cords. These may turn cancerous,
so specialist treatment is required. Hoarseness
or a change in voice lasting for more than
3 weeks needs treatment by a specialist.

Influenza virus Larynx Sites of upper respiratory tract infections Laryngitis
Colored micrograph of influenza viruses. A core of Most infections of the nose, sinus pharynx, and Endoscopic view of the inside of the larynx, which
RNA-genetic material (red) is surrounded by a larynx are caused by viruses and do not respond is inflamed due to acute infection. The vocal cords
spiked protein envelope (yellow) that can change to antibiotics. However, patients with underlying are the paired central white structures that
its structure to create a new strain of influenza. lung disease may be treated with antibiotics. resonate to produce vocal sounds.