How It Works - Book of the Human Body

5 TOP Welcome to the world When you need to breathe And relaaax Amino what now? Fight or flight
FACTS
1 A baby’s stress level during 2 Due to its blood-vessel- 3 After stressful situations, it’s 4 Adrenaline can be obtained from 5 The saying ‘fight or flight’ is
ADRENLINE birth is high and, as a result, constricting properties, adrenaline often a good idea to physically animals or synthesised in the lab. associated with adrenaline because
their adrenaline level is also is also used to treat breathing work off the adrenaline in your The chemical name for it is when we’re stressed we produce the
very high at this time. This difficulties associated with body so it doesn’t stay in your aminohydroxyphenylpropionic hormone in order that we can either
subsides post birth back down anaphylactic shock caused by system, keeping you awake at acid, which is represented with the get ready to defend ourselves or
to normal levels. allergic reactions. night, for example. chemical formula C9H13NO3. make a run for it.

Adrenaline Medulla Cortex

Discover the science behind your body’s At the core of the At the edge of the adrenal gland, the
amazing chemical coping mechanism adrenal gland, the cortex produces steroid hormones that
adrenal medulla include cortisol (for balancing blood sugar
produces, stores and and carb metabolism) and aldosterone
releases adrenaline. (for balancing the body’s salts and water).

Nestling on a layer of fat as adrenaline. Identified in 1900, Kidney
located just above each adrenaline is a fast-acting hormone
of your kidneys are the that helps the body deal with The organ that
body’s adrenal glands. unexpected stresses – not to mention filters waste
Around 8cm long, the adrenal glands high levels of excitement – by upping
produce hormones that affect your your heart rate and the flow of blood from the blood.
body’s consumption of energy as well to your muscles.
as your stress responses. Fat
Adrenal glands consist of two main The effect of this is that your blood
layers of hormone-secreting cells: the vessels and air passages dilate, Each adrenal
outer cortex and the inner medulla. meaning that more blood passes to gland is protected
While the cortex produces energy- the muscles and more oxygen gets to
balancing hormones, the medulla the lungs quicker, temporarily by a layer of fat.
produces a chemical called improving the body’s physical
epinephrine, which we know better performance and potentially saving
your life.

“Adrenaline is a fast-acting Your
hormone that helps the adrenal glands
body deal with stresses”

101

THE BODY AT WORK

How we breathe

Human
respiration

Respiration is crucial to an organism’s
survival. The process of respiration is the
transportation of oxygen from the air that
surrounds us into the tissue cells of our
body so that energy can be broken down

The primary organs used exercising, breathing rate increases 1. Nasal passage/
for respiration in humans and consequently so does heart rate oral cavity
are the lungs. Humans to ensure that oxygen reaches tissues
have two lungs, with the that need it. Oxygen is then used to These areas are where air
left lung being divided into two lobes break down glucose to provide
and the right into three. Lungs have energy for the body. This happens in enters into the body so that
between 300–500 million alveoli, the mitochondria of cells. Carbon
which is where gas exchange occurs. dioxide is one of the waste products oxygen can be transported into
Respiration of oxygen breaks into of this, which is why we get a build up
four main stages: ventilation, of this gas in our body that needs to and around the body to where
pulmonary gas exchange, gas be transported back into the lungs to
transportation and peripheral gas be exhaled. it’s needed. Carbon dioxide
exchange. Each stage is crucial in
getting oxygen to the body’s tissue, The body can also respire also exits through these areas.
and removing carbon dioxide. anaerobically, but this produces far
Ventilation and gas transportation less energy and instead of producing
need energy to occur, as the co2 as a byproduct, lactic acid is
diaphragm and the heart are used to produced. The body then takes time
facilitate these actions whereas gas to break this down after exertion has
exchanging is passive. As air is drawn finished as the body has a so-called
into the lungs at a rate of between 10- oxygen debt.
20 breaths per minute while resting,
through either your mouth or nose by 5. Alveoli
diaphragm contraction, and travels
through the pharynx, then the The alveoli are tiny little sacs which are situated
larynx, down the trachea, and into at the end of tubes inside the lungs and are in
one of the two main bronchial tubes. direct contact with blood. Oxygen and carbon
Mucus and cilia keep the lungs clean dioxide transfer to and from the blood stream
by catching dirt particles and through the alveoli.
sweeping them up the trachea.
When air reaches the lungs, oxygen Pulmonary How our
is diffused into the bloodstream artery lungs work
through the alveoli and carbon
dioxide is diffused from the blood Pulmonary Lungs are the major
into the lungs to be exhaled. Diffusion vein respiratory organ in humans
of gases occurs because of differing
pressures in the lungs and blood. This Capillary beds
is also the same when oxygen
diffuses into tissue around the body.
When blood has been oxygenated by
the lungs, it is transferred around the
body to where it is most needed in the
bloodstream. If the body is

102

5TOP Lung capacity The right lung We have excess Alveoli have massive We breathe 11,000
FACTS varies hugely is bigger lung capacity surface area litres of air per day

LUNGS 1 Dependant on sex and body 2 Interestingly, the left lung is 3 On average, humans only use 4 If one person’s entire 5 On average, one individual will
size, alongside external slightly smaller than the right in about one-eighth of the alveoli were laid out they would breathe in 11,000 litres of air in
factors such as altitude, lung the human body because the left capacity of our lungs for each have the surface area of about 70cm2 any given day. If they exercise
capacity ranges between lung has to make room for the breath so we have a large – that’s roughly the size of half a heavily during that day, this will
4,000 and 6,000cm3. heart to fit in. reserve volume. tennis court! increase further.

DID YOU KNOW? Trained free-divers can hold their breath underwater for up to nine minutes

2. Pharynx How do we breathe? Chest cavity
The intake of oxygen into the body is complex
This is part of both This is the space that
the respiratory and Breathing is not something that we have to the alveoli at the ends, which are the final is protected by the
digestive system. A flap think about, and indeed is controlled by muscle branching. The chest will be seen to rise
of connective tissue contractions in our body. Breathing is because of this lung expansion. Alveoli are ribs, where the lungs
called the epiglottis controlled by the diaphragm, which contracts surrounded by blood vessels, and oxygen and and heart are
closes over the trachea and expands on a regular, constant basis. carbon dioxide are then interchanged at this
to stop choking when When it contracts, the diaphragm pulls air into point between the lungs and the blood. Carbon situated. The space
an individual takes food dioxide removed from the blood stream changes as the
into their body. the lungs by a vacuum-like effect. The lungs and air that was breathed in but not
expand to fill the enlarged chest cavity used is then expelled from the lungs diaphragm moves.
3. Trachea and air is pulled right through by diaphragm expansion. Lungs
the maze of tubes that deflate back to a reduced size Rib cage
Air is pulled into the make up the when breathing out.
body through the nasal lungs to This is the bone
passages and then structure which
passes into the trachea. protects the organs.
The rib cage can
4. Bronchial tubes Lungs move slightly to © DK Images

These tubes lead to either the Deoxygenated blood allow for lung
left or the right lung. Air passes arrives back at the expansion.
through these tubes into the lungs, where another
lungs, where they pass gas exchange occurs at
through progressively smaller the alveoli. Carbon
and smaller tubes until they dioxide is removed and
reach the alveoli. oxygen is placed back
into the blood.

Diaphragm

This is a sheet of muscle situated
at the bottom of the rib cage
which contracts and expands to
draw air into the lungs.

© DK Images Heart

6. Ribs The heart pumps oxygenated
blood away from the lungs,
These provide protection around the body to tissue,
for the lungs and other where oxygen is needed to
internal organs situated break down glucose
in the chest cavity. into a usable form
of energy.
© DK Images
Tissue

Oxygen arrives
where energy is
needed, and a gas
exchange of
oxygen and carbon
dioxide occurs so
that aerobic
respiration can
occur within cells.

Why do we need oxygen?

We need oxygen to live as it is crucial for the release
of energy within the body

Although we can release energy through more than a few minutes, an individual will die.
anaerobic respiration temporarily, this method Oxygen is pumped around the body to be used
is inefficient and creates an oxygen debt that in cells that need to break down glucose so that
the body must repay after excess exercise or energy is provided for the tissue. The equation
exertion has ceased. If oxygen supply is cut off for that illustrates this is:

C6H12O6+6O2 = 6CO2+6H2O + energy

103

THE BODY AT WORK

Sweating / Dehydration

© Science Photo LibraryPore Skin
© DK Images
Sweat is Once the sweat is on the skin’s
released directly surface, its absorbed moisture
into the dermis
via the secretary evaporates, transferring the
duct, which then heat into the atmosphere.
filters through
the skin’s pores
to the surface.

Beads of sweat from the pores in
human skin, taken with a

scanning electron microscope

Why do we sweat?

As your doctor may tell you, it’s glandular…

Sweat is produced by dedicated sweat internal temperature of the body rises, secrete a Secretary Secretary part Nerve fibres
glands, and is a mechanism used salty, water-based substance to the skin’s surface. duct
primarily by the body to reduce its This liquid then cools the skin and the body This is where the Deliver messages to
internal temperature. There are two through evaporation, storing and then transferring Secreted sweat majority of the gland’s glands to produce
types of sweat gland in the human body, the excess heat into the atmosphere. sweat when the
eccrine gland and the apocrine gland. The former travels up to the secretary cells can body’s temp rises.
regulates body temperature, and is the primary Both the eccrine and apocrine sweat glands only be located.
source of excreted sweat, with the latter only appear in mammals and, if active over the majority skin via this duct.
secreting under emotional stresses, rather than of the animal’s body, act as the primary
those involved with body dehydration. thermoregulatory device. Certain mammals such
Eccrine sweat glands are controlled by the as dogs, cats and sheep only have eccrine glands in
sympathetic nervous system and, when the specific areas – such as paws and lips – warranting
the need to pant to control their temperature.

Dehydration Dangers of dehydration

How does a lack of water vary from mild to fatal?

What happens if we don’t drink enough? 1% Mild Thirst is triggered by
a concentration of

Just by breathing, salt and sugar levels going particles in the
sweating and urinating, haywire. Enzymatic activity is
the average person loses slowed, toxins accumulate more 2% Moderate blood, indicating a
ten cups of water a day. With H2O easily and even breathing can need to hydrate.
making up as much as 75 per cent become more difficult as the lungs
of our body, dehydration is a are having to work harder. 3% Other symptoms at
frequent risk. Water is integral in
maintaining our systems and it Babies and the elderly are most Dizziness Dry skin Headaches this level include
performs limitless functions. susceptible as their bodies are not
Essentially, dehydration strikes as resilient as others. It has been fatigue, a dry mouth
when your body takes in less fluid recommended to have eight
than it loses. The mineral balance glasses of water or two litres a day. 4% and constipation.
in your body becomes upset with More recent research is undecided
as to how much is exactly needed. 5% Severe Fever Racing pulse Lack of sweat

Too much H2O? Dehydration levels 6% Dehydration is Other symptoms
7% now so severe include sunken
Hydration is all about finding the perfect balance. 8% that IV fluid eyes, low blood
Too much hydration can be harmful as well as 9% replacement pressure and
too little; this is known as water intoxication. If 10% is necessary. dark urine.
too much liquid is in your body, nutrients such 11%
as electrolytes and sodium are diluted and the 12% Fatal Delirium Loss of Here symptoms
body suffers. Your cells bloat and expand and consciousness become much
can even burst, and it can be fatal if untreated. ? more extreme and
The best treatment is to take on IV fluids cognitive abilities
containing electrolytes. may also suffer.

Risk of heat exhaustion or
heat stroke is prevalent and
can even be fatal.

104

F5ATCOTPS Jet lag Mental state Latin name The living clock Time to take your pills

CIRCADIAN 1 Time zone changes can often 2 Health conditions such as 3 With these rhythms known to 4 In the 18th Century, a botanist 5 Doctors tell you to take medicine
RHYTHMS disrupt circadian rhythms. depression, bipolar disorder occur approximately every 24 called Carolus Linnaeus is said at a prescribed time because the
Your body clock may be out and seasonal affective hours, the phrase ‘circadian’ to have invented a living clock. human body clock can affect
of sync with your wristwatch, disorder (SAD) are all stems from Latin for ‘circa’, His garden could help him tell their effectiveness. Aspirins
but it will reset itself after a associated with abnormalities which means ‘about’, and ‘diem’, the time based on the flowers function better when taken early
few days. in circadian rhythms. which means ‘day’. he planted. in the morning.

DID YOU KNOW? The pineal gland, located near the centre of the brain, is about 8mm long and shaped like a pine cone

Circadian rhythms
How does our internal body clock tell us when to sleep? The sleep-
wake cycle
10.00 NOON
The variations in the amount of
High alertness 12.00 melatonin secreted by the body create

09.00 14.30 a daily rhythm of rising and falling
hormone levels. These hormones,
Highest testosterone Best co-ordination along with the SNC, affect appetite,
secretion here
body temperature and a lot else.
08.30
15.30
Bowel movement likely
Fastest reaction time

07.30

Melatonin secretion ends

06.45 17.00

Steep rise in blood Highest cardio-
pressure. Heart attacks vascular efficiency
are more likely to occur in and muscle strength
the morning than any
other time due to this rise
in blood pressure

06.00 18.00

18.30

Highest blood
pressure time

04.30 19.00

To conserve energy during Body temperature is
sleep, body temperature highest during the
drops. It is at its lowest just late afternoon
before waking
21.00
LARKS VS OWLS 02.00 00.00 22.30
With the fading of sunlight into
We all know that our genes make us Deepest sleep MIDNIGHT Bowel movements the evening, melatonin secretion
different, and this also affects our suppressed here begins – and increases tenfold –
individual natural rhythms. Some people making us sleepy
have a body clock that lasts longer than 24
hours, which means they tend to stay up Output rhythms:
later: these people are referred to as owls. physiology
Other people with shorter body clocks, behaviour
meanwhile, tend to rise earlier in the
morning: people like this are larks. 105

Circadian rhythms are biological changes that occur at roughly 24-hour Light © National Institute of General Medical Sciences
intervals, whether we’re aware of the time on our watch or not. These
changes, which are controlled by internal biological time-keeping Suprachiasmatic
systems, affect us physically, mentally and behaviourally. nucleus (SCN)
Located behind the eyes in the hypothalamus is a region of the brain called the
suprachiasmatic nucleus. No larger than a grain of rice, the SCN is a kind of master
body clock that controls all our other internal clocks, which in turn control our
circadian rhythms, or daily wake-sleep cycles. Circadian rhythms respond mainly
to light and dark cues but even if the body was monitored under conditions devoid
of day or night signals, our circadian rhythms still cycle in a period of around 24
hours. The retina in the eye senses light level information, which is relayed to the
SCN, which sends a signal to the pineal gland. This pea-sized gland, located
beneath the thalamus, is responsible for the secretion of melatonin – a hormone
that tells the body to sleep – and so at night when light levels fall, the production of
melatonin increases, telling us to head to bed…

THE BODY AT WORK

Human immune system

How your immune
system works

Your body is locked in a constant Physical
war against a viscous army defences

Human anatomy subscribes to the notion
that good fences make good neighbours.
Your skin, made up of tightly packed cells
and an antibacterial oil coating, keeps
most pathogens from ever setting foot in
body. Your body’s openings are well-
fortified too. Pathogens that you inhale
face a wall of mucus-covered membranes
in your respiratory tract, optimised to
trap germs. Pathogens that you digest end
up soaking in a bath of potent stomach
acid. Tears flush pathogens out of your
eyes, dousing bacteria with a harsh
enzyme for good measure.

It’s true: while you’re sitting around that take over host cells and replicate inside them; Just about everything in our environment is
watching TV, trillions of foreign invaders and fungi, a type of plant life. teeming with these microscopic intruders... including
are launching a full scale assault on the you. The bacteria in your stomach alone outnumber
trillions of cells that constitute ‘you’. Bacteria and viruses are by far the very worst all the cells in your body, ten-to-one. Yet, your scrappy
Collectively known as pathogens, these attackers offenders. Dangerous bacteria release toxins in the microscopic soldiers usually win the day against
include bacteria, single-celled creatures that live to body that cause diseases such as E. coli, anthrax, and pathogens, through a combination of sturdy barriers,
eat and reproduce; protists, larger single-cell the black plague. The cell damage from viruses causes brute force, and superior battlefield intelligence,
organisms; viruses, packets of genetic information measles, the flu and the common cold, among collectively dubbed the immune system.
numerous other diseases.

106

F5ATCOTPS The cure can Immunity soldiers You can ‘borrow’ It deals with internal It has trouble with
sometimes hurt are everywhere immunity troubles, too change
IMMUNE SYSTEM
1 Sneezing, coughing, a sore 2 A single drop of blood contains 3 Antibodies in breast milk give 4 In addition to fighting 5 Unfortunately you cannot
throat, and fever are all common around 375,000 white blood babies temporary immunity pathogens, T-cells fight the develop immunity to the
means of expelling pathogens, so cells, and blood constitutes for from diseases their mother is body’s own cancerous cells and flu and common cold
as annoying as they are, each seven per cent of your total immune to, preventing some cancer therapies boost because the viruses are
one is necessary. body weight. infancy infection. the number of T-cells. always mutating.

DID YOU KNOW? Dr Karl Landsteiner first identified the major human blood groups – A, B, AB and O – in 1901

The adaptive immune system

Fighting the good fight, and white blood cells are 2. Bacterium antigen
right on the front line…
These distinctive molecules allow your
When a pathogen is tough, wily, The B-cells flood your body 4. Engulfed immune system to recognise that the
or numerous enough to survive with antibodies, molecules that bacterium bacterium is something other than a body cell.
non-specific defences, it’s up to either disarm a specific pathogen
the adaptive immune system to or bind to it, marking it as a target During the initial 3. Macrophage 1. Bacterium
clean up the mess. The key forces for other white blood cells. When
in the adaptive immune system T-cells find their target, they lock inflammation reaction, These white blood Any bacteria that enter
are white blood cells called on and release toxic chemicals cells engulf and digest your body have
a macrophage engulfs
any pathogens they characteristic antigens
the bacterium.

lymphocytes. Unlike their that will destroy it. T-cells are come across. on their surface.

macrophage cousins, especially adept at destroying

lymphocytes are engineered to your body’s cells that are infected

attack only one specific type of with a virus.

pathogen. There are two types of This entire process takes

lymphocytes: B-cells and T-cells. several days to get going and may

These cells join the action take even longer to conclude. All

when macrophages pass along the while, the raging battle can

information about the invading make you feel terrible.

pathogen, through chemical Fortunately, the immune

messages called interleukins. system is engineered to

After engulfing a pathogen, a learn from the past. While

macrophage communicates your body is producing new 7. Non-
details about the pathogen’s B-cells and T-cells to fight the matching B-cells
antigens – telltale molecules that pathogens, it also produces
characterise a particular memory cells – copies of the Other B-cells, engineered to
pathogen. Based on this B-cells and T-cells, which stay in
attack other pathogens,

don’t recognise

information, the immune system the system after the pathogen is the antigen.

identifies specific B-cells and defeated. The next time that 5. Presented

T-cells equipped to recognise and pathogen shows up in your body, bacterium antigen

battle the pathogen. Once they these memory cells help launch a After engulfing the bacterium, the

are successfully identified, these counter-attack much more macrophage ‘presents’ the
cells rapidly reproduce, quickly. Your body can wipe out bacterium’s distinctive antigens,
assembling an army of cells that the invaders before any infection communicating the presence of
are ready and equipped to take takes hold. In other words, you the specific pathogen to B-cells.

down the attacker. develop immunity. 6. Matching B-cell 9. Memory cell
Vaccines accomplish the same
Non-specific The specific B-cell that The matching B-cell also
defences thing by giving you just enough recognises the antigen, and replicates to produce
pathogen exposure for you to can help defeat the pathogen,
develop memory cells, but not receives the message. memory cells, which will
enough to make you sick. rapidly produce copies of

itself if the specific

As good as your physical defence system is, pathogens bacteria ever returns.

do creep past it regularly. Your body initially responds How B-cells
with counterattacks known as non-specific defences, attack
so named because they don’t target a specific type
of pathogen. B-cells target and
destroy specific bacteria
After a breech – bacteria rushing in through a cut, for and other invaders
example – cells release chemicals called inflammatory
mediators. This triggers the chief non-specific defence,
known as inflammation. Within minutes of a breach,

your blood vessels dilate, allowing blood and other fluid

to flow into the tissue around the cut.

The rush of fluid in inflammation carries various types 11. Phagocyte 10. Antibodies 8. Plasma cell
of white blood cells, which get to work destroying
intruders. The biggest and toughest of the bunch are White blood cells The plasma cells release The matching B-cell
macrophages, white blood cells with an insatiable called phagocytes antibodies, which replicates itself,
appetite for foreign particles. When a macrophage detects recognise the antibody disable the bacteria by
a bacterium’s telltale chemical trail, it grabs the intruder, marker, engulf the
engulfs it, takes it apart with chemical enzymes, and bacteria, and
digest them.

spits out the indigestible parts. A single macrophage can latching on to their creating many

swallow up about 100 bacteria before its own digestive antigens. The antibodies plasma cells to fight
chemicals destroy it from within. also mark the bacteria all the bacteria of this
for destruction.
type in the body.

107

THE BODY AT WORK

Human immune system

Your tonsils can help 1. Tonsils
fight bacteria
Lymphoid tissue loaded with
lymphocytes, which attack
bacteria that get into the body
through your nose or mouth.

© Klem 2007
© Ed Uthman, MD
2. Left subclavian vein 6. Lymph
Disorders of © DK Images node cluster
the immune One of two large veins that serve
system as the re-entry point for lymph Located along lymph vessels
returning to the bloodstream. throughout the body, lymph nodes
Who watches the filter lymph as it makes its way back
watchmen? 3. Right lymphatic duct
into the bloodstream.
The immune system is a powerful set of Passageway leading from lymph vessels
defences, so when it malfunctions, it to the right subclavian vein. 7. Left
can do as much harm as a disease. lymphatic duct
Allergies are the result of an overzealous 4. Right subclavian vein
immune system. In response to Passageway leading from
something relatively benign, like The second of the two subclavian lymph vessels to the left
pollen, the immune system triggers veins, this one taking the opposite subclavian vein.
excessive measures to expel the path to its twin.
pathogen. On the extreme end, allergies 8. Thymus gland
may cause anaphylactic shock, a 5. Spleen
potentially deadly drop in blood Organ that provides area for
pressure, sometimes accompanied by An organ that houses white lymphocytes produced by bone
breathing difficulty and loss of blood cells that attack
consciousness. In autoimmune pathogens in the marrow to mature into
disorders such as rheumatoid arthritis, body’s bloodstream. specialised T-cells.
the immune system fails to recognise
the body’s own cells and attacks them. 10. Lymph vessels 9. Thoracic duct

In an allergic reaction, the body may resort to Lymph collects in tiny capillaries, The largest lymph vessel
sneezing to expel a fairly harmless pathogen which expand into larger vessels. in the body.
Skeletal muscles move lymph
108 through these vessels, back into 11. Peyer’s patch
the bloodstream.
Nodules of lymphoid tissue supporting
The white blood cells that battle pathogens
lymphatic
system in the intestinal tract.

The lymphatic system is a network of 12. Bone marrow
organs and vessels that collects lymph
– fluid that has drained from the The site of all white blood
bloodstream into bodily tissues – and cell production.
returns it to your bloodstream. It also
plays a key role in your immune Lymph
system, filtering pathogens from nodes
lymph and providing a home-base for explained
disease-fighting lymphocytes.
Lymph nodes
filter out

pathogens moving
through your
lymph vessels

Your immune system depends
on these .04-1-inch swellings to
fight all manner of pathogens.

As lymph makes its way
through a network of fibres in

the node, white blood cells
filter it, destroying any
pathogens they find.

HEAD MOST DEADLY © National Photo Company 1. Influenza MOST CONTAGIOUS 2. Measles MOST COMMON 3. Tuberculosis

2HEAD The flu kills hundreds of One person infected with Excavated Ancient Egyptian
GERMS AND thousands of people in a measles will spread the virus mummies show signs of
VIRUSES good year. And every to just about every tuberculosis, and the disease
once in a while, a virulent unvaccinated person they is still thriving today. Around
form can take out tens of encounter. Luckily, the 2 billion people around the
millions of people. vaccine is very effective. world are infected.

DID YOU KNOW? In 2008, approximately 33 million people worldwide were living with HIV or AIDS

3. Capsule 1. Flagella Know your
enemy:
Protects the Flagella swish
inner contents for movement Bacteria

2. Pili Bacteria are the smallest and, by far, the most populous form of life
on Earth. Right now, there are trillions of the single-celled creatures
The pili anchor to crawling on and in you. In fact, they constitute about four pounds of
cell surfaces your total body weight. To the left is a look at bacteria anatomy…

4. Nucleoid What is HIV…

The nucleoid contains … and how does it affect the
genetic material immune system?

6. Cell wall The human immunodeficiency virus (HIV) is a retrovirus (a virus
carrying ribonucleic acid, or RNA as it’s known), transmitted
Provides structural through bodily fluids. Like other deadly viruses, HIV invades
integrity cells and multiplies rapidly inside. Specifically, HIV infects cells
with CD4 molecules on their surface, which includes infection-
7. Cell membrane fighting helper T-cells. HIV destroys the host cell, and the virus
copies go on to infect other cells. As the virus destroys helper
The cell’s interior barrier T-cells, it steadily weakens the immune system. If enough
T-cells are lost, the body becomes highly susceptible to a range
of infections, a condition known as acquired immune deficiency
syndrome (AIDS).

8. Cytoplasm

5. Ribosomes Home of all material
outside the nucleoid
These help with protein
manufacturing

Bacteria
anatomyInside these

microorganisms

1 3 Major points of the lymph node
2 4
1. Outgoing lymph 7. Sinus
11 5 vessel
10 6 A channel that slows the
The vessel that carries flow of lymph, giving
9 7 filtered lymph out of the macrophages the
lymph node opportunity to destroy any
88 detected pathogens Scanning electron micrograph of HIV-1 budding (in green) from cultured
2. Valve lymphocyte. This image has been coloured to highlight the most
8 8. Incoming lymph important features. Multiple round bumps on the cell surface represent
A structure that prevents vessel sites of assembly and budding of virions.
lymph from flowing back
into the lymph node A vessel that carries lymph 109
into the lymph node
3. Vein
9. Lymphocyte
Passageway for blood
leaving the lymph node The T-cells, B-cells and
natural killer cells that
4. Artery fight infection

Supply of incoming blood 10. Germinal centre
for the lymph node
This is the site of
5. Reticular fibres lymphocyte multiplication
and maturation
Divides the lymph node
into individual cells 11. Macrophage

6. Capsule Large white blood cells that
engulf and destroy any
The protective, shielding detected pathogens
fibres that surround the
lymph node

THE BODY AT WORK

Mending bones

Bone fracture
healing process

Learn how your body mends broken bones

If a bone has too much pressure put gradually fuse together, like a bridge being All-star cast
on it, there is a chance it will break. constructed from either side of a river until both
Your body has ways of repairing ends meet in the middle. Most breaks on an arm or a leg will have a plaster
these breaks, but it takes time and cast put on them to prevent the bone from
care. There are different kinds of break, ranging Once both sections of bone are connected setting at a wonky angle or not setting at all.
from a hairline fracture to a fully shattered again, specialised cells called osteoblasts enter to
bone, but they all mend in a similar way. produce bone cells. These new cells replace the It will generally be made from plaster of Paris.
As a bone breaks, the blood vessels are also callus, returning the bone to its original shape. This is a mixture of water and gypsum that sets
severed. Blood leaks out and forms a clot called really hard once it has dried. The broken bone is
a fracture haematoma. This stops blood flow to Much like repairing a broken toy with glue, bandaged and the wet mixture is applied to the
the area and also helps keep both pieces of bone the bone needs to be kept straight and steady gauze. Once it has dried then it should provide
aligned, ready for healing. for the fusion to happen correctly. This is why safety and stability for the bone.
The body then makes fibrous cells and doctors will put a cast on the broken bone. The
cartilage, which reinforce the bond and cast provides essential support, protection and Fibreglass is an increasingly common cast
strengthen it. This creates a callus, which is stability, ensuring the broken bone doesn’t material. As with the plaster cast, the broken
essentially a weakened bone. Over time, the move. A cast will generally stay on for a few bone is bandaged up. Next, another bandage,
callus builds up and the two parts of the bone weeks until the bond has become strong made of fibreglass and layered with resin, is
enough, but it could take months for a properly soaked in water. This makes it flexible enough to
set bone to fully recover. be wrapped around the bone before it hardens as
it dries. This is much lighter than a plaster cast
and the outer layer is waterproof.

The stages of bone repair

Blood Marrow New Healed
clot blood fracture
forms Internal callus vessels
(fibrous tissue
and cartilage)

Ruptured Hard
blood bone
vessels callus

External Blood flow
callus improves

Blood clot Tissue growth Remodelling © Thinkstock

When a bone breaks, the blood vessels A few days later, the blood clot – called the fracture Bone-forming cells called osteoblasts work in
that run through the bone are severed. haematoma – is gradually replaced by tougher teams to build a new bone, creating a more solid
The blood forms a clot to align the bones. tissue, which becomes a soft callus. Fibrous tissue structure called a hard bone callus. It takes several
This creates a solid yet weak structure to and cartilage are produced that begin to bridge the months to fill the cavity with harder bone,
prepare for mending. The clot also cuts off gap between the fractured ends. New blood vessels strengthened by nutrients like calcium and
blood flow to the edges of the broken bone, begin to form and the callus usually lasts around phosphorus. However, it may take longer for the
so these cells die. three weeks. bone to be completely healed.

110

5TOP Pokémon Protein from food Protein we need Biuret test Genome studies
FACTS
1 Speedy Pokémon character 2 We get protein from meat, 3 Your body makes thousands 4 The Biuret test is a chemical 5 From studies into the human
PROTEIN Pikachu had a protein named fish, eggs, nuts and dairy of proteins every day. For each form of analysis that is used to genomes sequenced so far, it
after it in 2008. The protein, products. We digest the 1kg you weigh, you typically measure the amount of has been discovered that the
pikachurin, is used in kinetic proteins into amino acids, require 1g of protein. So daily a protein that is present in food. body contains over 2 million
vision, which, aptly, is the which we later use to replace 70kg man must manufacture It works out protein levels by proteins, coded by just
detection of fast objects. these proteins in our bodies. 70g of protein for his needs. analysing the peptide bonds. 20,000-25,000 genes.

DID YOU KNOW? Around half of your body’s ‘non-water’ mass is made up of proteins

1. Cell Protein production

The body is made up of millions Protein is generated in the nucleus of a cell using genetic
of cells, none of which could coding information held within our DNA. To produce
survive without protein, for
repair and replacement. protein, DNA unravels to allow messenger RNA (or mRNA) to
copy it and form a template. This template is translated by
ribosomes into amino acids, which then line up to form a
protein. Parts of DNA code will
serve as punctuation, telling
the ribosome when to start
and stop, and some parts
will instruct the cell how
frequently it must produce
the specific protein.

6. mRNA 7. Ribosome 5. DNA

This type of genetic acid This is the ‘protein-making DNA (deoxyribonucleic
forms a template based on machine’ in the cell. It uses acid) holds the information
DNA sequences, which is mRNA templates to synthesise
then used to produce amino the specific protein needed. necessary for amino acid
acids by the ribosome. – and ultimately protein
– production in the letter

sequence in its structure.

9. Protein 8. Amino acid 4. Nucleosomes

Proteins are made up of long chains of These small molecules These are balls formed of
amino acids. Each protein has a specific combine in specific string DNA strands and histones
function which suits its role and is sequences to generate the (spool-like proteins) which
crucial to our bodies being able to different types of protein.
operate effectively. sit inside chromosomes.

2. Nucleus 3. Chromosome Why are © SPL
amino acids
This is the control centre of Most human cells have a set of important?
the cell where all important 46 chromosomes and these
genetic data is stored. Amino acids are vital to
contain our genetic information our bodies being able to
which, among other things, operate as they are the
building blocks of
instructs the cell which protein proteins. Each type of
to make and also how. amino acid performs a
different job, which aids
How do we make protein? protein activity in the
body and determines the
Proteins are the building blocks of the human body, protein’s primary
but how do we go about manufacturing them? function(s). Without these,
proteins would not be
Proteins are large complex molecules made up of a and T) and these short sequences, which are known as triplets able to help the body with
chain of amino acids. Every cell in our body needs or codons, then code mRNA templates; these templates are movement, defence
protein to stay alive as it is necessary for tissue ‘translated’ by cell ribosomes into amino acids. against disease,
repair and replacing dead cells. processing food or
They have many other functions as well as aiding cell repair Each protein is made up of hundreds of thousands of amino co-ordinating general
and production including forming antibodies to help fight off acids, which are in long chains. There are 20 different types of growth and development.
disease, forming enzymes which speed up or trigger chemical amino acid that can be combined to build a protein and it is the
reactions and co-ordinating processes within the body (via sequence of amino acids that determines each protein’s unique There are nine
hormone regulation, for instance). Proteins also provide three-dimensional structure and its function. essential amino acids for
support for cells and form structural elements of the body, such humans that must be
as nails and teeth, as well as facilitating the transportation of However, not all amino acids can be made by the body. The absorbed from external
some small molecules around various systems. ones that need to be consumed via our diet are called essential protein sources (eg meat/
We build proteins using information encoded in our genetic amino acids. If possible, the body will also conserve energy by fish) as they cannot be
code. DNA code utilises groups of three letters (a mix of A, G, C using amino acids from food rather than producing them itself. synthesised by the body.
Protein deficiency can cause diseases such as kwashiorkor, a Without the required
form of malnutrition common in poverty-stricken areas. amount of amino acids,
the body can really suffer.

111

THE BODY AT WORK

Cell division explained

The cell cycle

Inside one of the body’s most vital processes

The continuous cycle of cell Cell duplication
division and growth is essential
to all life on Earth. Without it, no Explore the key stages of mitosis now
organism ont he planet would be
able to reproduce or develop. The cell cycle Prophase Prometaphase Metaphase Anaphase
consists of three main stages: interphase,
mitosis and cytokinesis. Chromosomes The nuclear envelope In this phase, all the Now, the spindle fibres
During interphase, the cell expands and condense, becoming breaks down and spindle spindle fibres are pull the chromosomes
makes the new proteins and organelles it will thicker and shorter. fibres extend from attached and the apart, with the
need for division. It then makes copies of its Sister chromatids form either side of the cell to chromosomes are chromatids moving to
chromosomes, doubling the amount of DNA in when the chromosomes attach to the middle of arranged in a line along opposite ends or ‘poles’
the cell and ensuring the conditions are right replicate themselves. each chromatid. the equator of the cell. of the cell.
to begin the next phase.
In mitosis, the membrane surrounding the
nucleus breaks down, exposing the
chromosomes, which are pulled to opposite
sides of the cell by tiny spindle fibres. A new
nuclear envelope then forms around the
chromosomes at each end of the cell. During
cytokinesis the cytoplasm splits in half to
create two ‘daughter’ cells, each with their own
nucleus and organelles.
The cycle is managed by regulating enzymes
known as CDKs . These act as a checkpoint
between the phases of division, giving the
signal for the next stage in the cycle to begin.
The cell cycle of prokaryotic cells (those
without a nucleus) is slightly different. Bacteria
and other prokaryotes divide via a process
called binary fission, in which the cell
duplicates its genetic material before doubling
in size and splitting in two. Meiosis is another
type of cell division and is concerned with
sexual reproduction as opposed to the asexual
organic growth of tissue in mitosis.

Cancer and the cycle

If the cell cycle goes wrong, cancerous
tumours are a possible consequence. It all
depends on the levels of proteins in the cycle. A
protein called p53 halts the process if DNA is
damaged. This provides time for the protein to
repair the DNA as the cells are then killed off
and the cycle begins anew. On the rare
occasions this process fails, cells can
reproduce at a rapid rate and tumours can
form. Chemo- and radiotherapy work by
destroying these mutated cells. A p53 mutation
is the most frequent one leading to cancer. An
extreme case is Li Fraumeni syndrome, where
a genetic defect in p53 leads to a high
frequency of cancer in those affected.

112

STRANGE What is apoptosis? Answer:
BUT TRUE
A Another type of cell division B Programmed Essentially a cell committing suicide, apoptosis is a
APPETITE FOR SELF- cell death C A new type of soft drink controlled biological system that kills off unneeded
DESTRUCTION or excess cells. One example is the removal of
webbing in between your fingers and toes before
you are born.

DID YOU KNOW? A common theory is that every living cell is descended from a single ancestral cell from 3-4bn years ago

Every step of the cell An expert’s view
division cycle is vital for

life as we know it

Paul Nurse, Nobel Prize winner and director of the Francis Crick Institute, chats
about cell cycle

What is the cell cycle? Why do skin cells divide so quickly and nerve
The cell is the basic unit of life for all living things. cells so slowly?
One of its many properties is the ability to reproduce. Cells change at varying rates and some nerve cells
The cell cycle is a series of processes that occur barely divide at all. This is one reason why it is
between the birth of the cell and its division into two. difficult to regenerate the nervous system when it
becomes damaged. Because the body has to deal
What is mitosis? with cuts and abrasions, it is much easier to get skin
Mitosis describes what happens near the end of the cells to divide.
cycle. The replicated chromosomes are separated
from each other into opposite ends of the cell just What is tissue culture and why is it important?
before the cell divides. It is simply a way of growing cells from animals and
plants in test tubes. They will divide under these
What are the different parts of the cycle? circumstances so you can study the cell cycle away
The other major part occurs before mitosis and is the from the complexities of an animal or plant.
process in which the DNA that makes up the
chromosomes replicates itself. This is called the What are the differences between plant and
S-phase or DNA synthetic phase [which is part of animal cell cycles?
interphase]. The S-phase replicates and mitosis Fundamentally, not very much. They both undergo
separates and divides. the same processes but are subject to different
overall controls.
What is the difference between mitosis and
meiosis and does cell division occur in both? What is proteolysis and how does that
Meiosis is usually considered to be the mitotic full mechanism help the cell cycle?
cycle and also leads towards cell reproduction. It is a biochemical mechanism that breaks down
However, in meiosis there are two M-phases or protein. It takes away certain proteins as part of a
divisions so the number of DNA and chromosomes regulatory system for a variety of biological process
are halved. Meiosis uses gametes for fertilisation in such as the cell cycle. It is used at the end of the
diploid cells in animal and plants. cycle to destroy excess protein and prepare for the
next cycle.
Does it occur in eukaryotic or prokaryotic cells?
Only in eukaryotic cells. In prokaryotic cells there is a You discovered CDK (Cyclin-dependent kinase).
cell cycle but it is not mitosis. This [process] is How do they contribute to the cell cycle?
simply the copying of DNA and then a much less CDK is a type of enzyme and my research group was
obvious separation of the copied DNA into the two involved in discovering that they were the major
divided cells. regulators in the cycle. CDK brings about the S-phase
and mitosis and controls them.
Why did you use yeast in your experiments?
Yeast is a very simple eukaryote, which reproduces How can the cycle help understand potential
in much the same way as more complex cells in us. It cures for cancer?
only has 5,000 genes compared to our 25,000. It To understand cancer, you have to be able to
simplifies cell division so is extremely convenient to understand the cell cycle. Crudely blocking the cell
study. It’s got fantastic genetics and genomics, cycle is a problem as a therapy as our body is full of
which allow you to investigate complicated other cells that have to divide.
processes like the cell cycle.

Telophase Cytokinesis Paul Nurse is also the © Dreamstime; BBC; Thinkstock; Dr. Cecil Fox; Corbis
former director of Cancer
The two new sets of The cytoplasm divides Research UK and president
chromosomes form and two or more of the Royal Society
groups at each pole and daughter cells are
a new envelope forms produced. Mitosis and
around each as the the cell cycle have now
spindle disappears. reached their end.

113

THE BODY AT WORK

Blood cells explained

How do white Monocyte
blood cells work?
One of the body’s main defences against infection and Monocytes help prepare us
foreign pathogens, how do these cells protect our bodies? for another infection by
presenting pathogens to the
body, so that antibodies can
be created. Later in their life,
monocytes move from the
bloodstream into tissue,
and then evolve into
macrophages which can
conduct phagocytosis.

White blood cells, or leukocytes, are Types of leukocyte
the body’s primary form of defence
against disease. When the body is Different kinds of WBC have different roles, which
invaded by a pathogen of any kind, the complement one another to defend the body
white blood cells attack in a variety of ways; some
produce antibodies, while others surround and Lymphocyte
ultimately devour the pathogens whole.
In total, there are five types of white blood cell These release antibodies
(WBC), and each cell works in a different way to as well as attack virus and
fight a variety of threats. These five cells sit in two tumour cells through three
groupings: the granulocytes and the differing types of cell. As a
agranulocytes. The groups are determined based group, they are some of
on whether a cell has ‘granules’ in the cytoplasm. the longest lived of the
These granules are digestive enzymes that help white blood cells with the
break down pathogens. Neutrophils, eosinophils memory cells surviving for
and basophils are all granulocytes, the enzymes years to allow the body to
in which also give them a distinct colouration defend itself if repeat
which the agranulocytes do not have. attacks occur.
As the most common WBC, neutrophils make up
between 55 and 70 per cent of the white blood cells
in a normal healthy individual, with the other four
types (eosinophils, basophils, monocytes and
lymphocytes) making up the rest. Neutrophils are
the primary responders to infection, actively
moving to the site of infection following a call from
mast cells after a pathogen is initially discovered.
They consume bacteria and fungus that has
broken through the body’s barriers in a process
called phagocytosis.
Lymphocytes – the second-most common kind
of leukocyte – possess three types of defence cells:
B cells, T cells and natural killer cells. B cells
release antibodies and activate T cells, while T
cells attack diseases such as viruses and tumours
when directed, and regulatory T cells ensure the
immune system returns to normal after an attack.
Natural killer cells, meanwhile, aid T cell response
by also attacking virus-infected and tumour cells,
which lack a marker known as MHC.
The remaining types of leukocyte release
chemicals such as histamine, preparing the body
for future infection, as well as attacking other
causes of illness like parasites.

“Natural killer cells Eosinophil
aid T cell response
by also attacking Eosinophils are the white
virus-infected and blood cells that primarily
tumour cells” deal with parasitic
infections. They also have
a role in allergic reactions.
They make up a fairly small
percentage of the total
white blood cells in our
body – about 2.3 per cent.

114

THE NEUTROPHIL
STATS
6 80mm 4 in 1,000LIFETIME (HOURS)
LEUKOCYTES MACROPHAGE WBCS WHICH
DIAMETER ARE BASOPHILS

BLOOD

1% 5-20 7,000COMPOSITION
BACTERIA CONSUMED NUMBER OF WBCS IN
BY EACH NEUTROPHIL A DROP OF BLOOD

DID YOU KNOW? WBCs have colour but appear white when blood is put through a centrifuge, hence their group name

White blood cells at work

The body has various outer defences against infection, including the
external barrier of the skin, but what happens when this is breached?

Skin breach Mast cells WBCs arrive Macrophages Healing
consume bacteria
A foreign object breaks Mast cells release cytokines Macrophages move to the Following removal of the
through the skin, and then WBCs are called site via the bloodstream to Bacteria are absorbed into bacteria, the body will start
introducing bacteria (shown into action to ensure the start defending against to heal the break in the skin
in green) into the body. infection does not spread. invading bacteria. cytoplasm and broken to prevent further infection.

down by the macrophages.

A microscopic illustration
of a neutrophil – the most
abundant WBC

Basophil

Basophils are involved in
allergic response via

releasing histamine and
heparin into the

bloodstream. Their
functions are not fully

known and they only
account for 0.4 per cent of

the body’s white blood
cells. Their granules

appear blue when viewed
under a microscope.

A faulty immune system

Neutrophil If the immune system stops working We can often treat these conditions with © SPL; Thinkstock
properly, we are at risk of becoming ill. immunosuppressants, which deactivate
Neutrophils are the most However, another problem is if the immune elements of the immune system to stop the
common of the leukocytes. system actually goes into overdrive and body attacking itself. However, there are
They have a short life span starts attacking the individual’s cells, drawbacks with this treatment as, if the
mistaking them for pathogens. There are a person exposes themselves to another
so need to be constantly large number of autoimmune ailments seen pathogen, they would not have the normal
produced by the bone across the world, such as Crohn’s disease, white blood cell response. Consequently,
psoriasis, lupus and some cases of arthritis, the individual is less likely to be able to fight
marrow. Their granules as well as a large number of diseases that normally low-risk infections and, depending
appear pink and the cell are suspected to have autoimmune roots. on the pathogen, they can even be fatal.

has multi-lobed nuclei
which make them easily
differentiated from other
types of white blood cell.

115

THE BODY AT WORK

The science of genetics

GENETICSTHE SCIENCE OF
From inheritance to genetic diseases, what secrets are hidden
in our genes and how do they determine who we are?

116

RECORD 150bn THE LONGEST GENOME
BREAKERS
An ordinary-looking white flower, Paris japonica, has the
GIANT GENOME longest known genome with 150 billion base pairs. If
stretched out it would measure over 91 metres (300 feet)!

DID YOU KNOW? If all 46 human chromosomes were stitched together and stretched they would measure nearly 2m (6.6ft)

Genes define who we are. They are How is our genetic code stored?
the basic unit of heredity, each
containing a coded set of Genetic information is coded into DNA using just four nucleobases: A, C, G and T
instructions to make a protein.
Humans have an estimated 20,500 genes, Chromosome
varying in length from a few hundred to more
than 2 million base pairs. They affect all Humans have 46
aspects of our physiology, providing the code chromosomes – 23 pairs
that determines our physical appearance, the containing around
biochemical reactions that occur inside our 20,500 genes.
cells and even, many argue, our personalities.
Every individual has two copies of every gene Double stranded Nucleus
– one inherited from each parent. Within the
population there are several alleles of each DNA has two complementary strands Surrounded by a double-
gene – that is, different forms of the same code, – one forms a template to make the thickness membrane, the
with a number of minor alterations in the other, allowing accurate replication. nucleus contains the genetic
sequence. These alleles perform the same information of the cell.
underlying function, but it is the subtle
differences that make each of us unique. Base pairs
Inside each of our cells (except red blood
cells) is a nucleus, the core which contains our The bases of DNA
genetic information: deoxyribonucleic acid are always found
(DNA). DNA is a four-letter code made up of in pairs: adenine
bases: adenine (A), guanine (G), cytosine (C) and pairs with thymine,
thymine (T). As molecular biologist Francis and guanine pairs
Crick once put it, “DNA makes RNA, RNA makes
protein and proteins make us.” Our genes are with cytosine.
stored in groups of several thousand on 23 pairs
of chromosomes in the nucleus, so when a cell Double helix
needs to use one particular gene, it makes a
temporary copy of the sequence in the form of DNA is arranged in a double helix
shape, with the bases forming the
ladder-like rungs in the centre.

DNA’s chemical structure Nucleotide

We put deoxyribonucleic acid under the microscope DNA is a polymer made up of
building blocks called nucleotides.
Phosphate

Phosphate groups
link the sugars of
adjacent nucleotides
together, forming a
phosphate backbone.

T A Hydrogen bond

Sugar Nucleobase Two bases interact with
each other by hydrogen
Each base is attached Each nucleotide contains a bonds (weak electrostatic
to a five-carbon sugar base, which can be one of four: interactions that hold the
called deoxyribose. adenine (A), thymine (T), strands of DNA together).
guanine (G) or cytosine (C).
117

THE BODY AT WORK

The science of genetics

ribonucleic acid (RNA). This copy contains all of fully understood, but having the genome Genetic mutations are the source of variation
the information required to make a protein – available to study is making the task of in all organisms. Most genetic mutation occurs
the building blocks of the human body. identifying genetic risk factors much easier. as the DNA is being copied, when cells prepare
to divide. The molecular machinery responsible
The Human Genome Project aimed to map Interestingly, the Human Genome Project for duplicating DNA is prone to errors, and often
the entire human genome; this map is discovered we have far fewer genes than first makes mistakes, resulting in changes to the
effectively a blueprint for making a human. predicted; in fact, only two per cent of our DNA sequence. These can be as simple as
Using the information hidden within our genome codes for proteins. The remainder of accidentally substituting one base for another
genetic code, scientists have been able to the DNA is known as ‘non-coding’ and serves (eg A for G), or can be much larger errors, like
identify genes that contribute to various other functions. In many human genes are adding or deleting bases. Cells have repair
diseases. By logging common genetic variation non-coding regions called introns, and machinery to correct errors as they occur, and
in the human population, researchers have between genes there is intergenic DNA. One even to kill the cell if it makes a big mistake, but
been able to identify over 1,800 disease- proposed function is that these sequences act despite this some errors still slip through.
associated genes, affecting illnesses ranging as a buffer to protect the important genetic
from breast cancer to Alzheimer’s. The information from mutation. Other non-coding Throughout your life you will acquire many
underlying genetic influences that affect DNA acts as switches, helping the cell to turn mutations in your cells. Many of these are
complex diseases like heart disease are not yet genes on and off at the right times. completely harmless, either occurring in

The Human Mapping the human genome Chicken
Genome
Project How does our genetic makeup compare to that of other creatures? Despite the fact
that we are not
The Human Genome Project, an Zebrafish closely related to
initiative to map the sequence of birds, the chicken
the entire human genetic code, Divergence between fish and still has regions of
began in 1990 and was completed mammals occurred very early DNA that are quite
in 2003. The 3.3-billion base pair in evolution, so similarities in similar to ours.
sequence was broken into our genes are very
sections of around 150,000 base fragmented. Dog
pairs in length and the sequence
for each identified. These were Human Some regions of the
then joined and used to map the canine genome are
information on to chromosomes This ring represents very different to ours,
to determine which genes were the genes on a but the pink bands
found on each – and in what order. human chromosome, show an area that has
The genome map (right) shows a with the numbers
human chromosome compared providing a been conserved.
with other animals; the colours representation
are a ‘heat map’ demonstrating of scale.
areas where genetic information
has been conserved through
evolution (the more fragmented
the pattern, the more differences
there are in the genetic code).

Chimpanzee Rat

One of our closest living The mouse and rat genomes
relatives – the solid bands have similar patterns,
demonstrate we share a
great deal of genetic demonstrating these rodents’
information (ie 98 per cent). close evolutionary relationship.

Mouse

There is less in common between
human and mouse (90 per cent),
but we are sufficiently similar that
mice make a good scientific model
for studying human disease.

118

DKEATYES 1865 1905 1953 1983 2003

GENETICS HISTORY Gregor Mendel, the father of William Bateson is the first Francis Crick (right) and Polymerase chain reaction Completion of the
modern genetics, observes person to use the term James Watson reveal the (PCR) is invented, enabling Human Genome Project
patterns of genetic inheritance double helix structure of small DNA samples to be provides access to the
in peas grown in his garden. ‘genetics’ to describe the study human DNA blueprint.
of biological inheritance. DNA using X-rays. amplified for testing.

DID YOU KNOW? Humans share 98 per cent genetic similarity with chimpanzees but just seven per cent with E coli

non-coding regions of DNA, or changing the mutant gene, which gave them black wings; A single nucleotide mutation causes
gene so nominally that the protein is virtually this made them an easy target for predators and haemoglobin, the protein involved in binding
unaffected. However, some mutations do lead kept their numbers low. When factories began oxygen in red blood cells, to misfold. Instead of
to disease (see ‘When genes go wrong’ box). to cover the trees in soot, however, the light- forming its proper shape, the haemoglobin
coloured moths struggled to hide themselves clumps together, causing red blood cells to
If mutations are introduced into the sperm against the newly blackened environment, so deform. They then have trouble fitting through
and egg cells they can be passed on to the next black moths flourished. They survived much narrow capillaries and often become damaged
generation. However, not all mutations are bad, longer, enabling them to pass on their mutation or destroyed. However, this genetic mutation
and this process of randomly introduced to their offspring and altering the gene pool. persists in the population because it has a
changes in the DNA sequence provides the protective effect against malaria. The malaria
biological underpinning that supports Darwin’s It is easy to see how a genetic change like the parasite spends part of its life cycle inside red
theory of evolution. This is most easily observed one that occurred in the peppered moth could blood cells and, when sickle cells rupture, it
in animals. Take, for example, the peppered give an advantage to a species, but what about prevents the parasite from reproducing.
moth. Before the Industrial Revolution the genetic diseases? Even these can work to our Individuals with one copy of the sickle cell gene
majority of these moths had white wings, advantage. A good example is sickle cell and one copy of the healthy haemoglobin gene
enabling them to hide against light-coloured anaemia – a genetic disorder that’s quite have few symptoms of sickle cell anaemia,
trees and lichens. However, a minority had a common in the African population.

Using genetics to Why do we look
convict criminals like our parents?

Forensic scientists can use traces of DNA to It’s a common misconception that we inherit
identify individuals involved in criminal activity. entire features from our parents – eg “You have
Only about 0.1 per cent of the genome differs your father’s eyes.” Actually inheritance is much
between individuals, so rather than sequencing more complicated – several genes work together
the entire genome, scientists take 13 DNA to create traits in physical appearance; even eye
regions that are known to vary between colour isn’t just down to one gene that codes for
different people in order to create a ‘DNA ‘blue’, ‘brown’ or ‘green’, etc. The combinations of
fingerprint’. In each of these regions there are genes from both of our parents create a mixture of
two to 13 nucleotides in a repeating pattern their traits. However, there are some examples of
hundreds of bases long – the length varies single genes that do dictate an obvious physical
between individuals. Small pieces of DNA – characteristic all on their own. These are known as
referred to as probes – are used to identify Mendelian traits, after the scientist Gregor Mendel
these repeats and the length of each is who studied genetic inheritance in peas in the
determined by a technique called polymerase 1800s. One such trait is albinism – the absence of
chain reaction (PCR). The odds that two people pigment in the skin, hair and eyes due to a defect
will have exactly the same 13-region profile is in the protein that makes melanin.
thought to be one in a billion or even less, so if
all 13 regions are found to be a match then Carrier parents
scientists can be fairly confident that they can
tie a person to a crime scene. Each parent carries the
albinism gene (dark pink), but
Carrier children
they have one normal gene
Two out of four will be (light pink), so they are able
carriers, like their parents,
with one normal and one to make melanin.
faulty gene.
Gametes
Healthy child
Each child inherits one
One in four children will gene from the mother and
receive one healthy gene
from the father and one one from the father.
from the mother.
Affected child

One in four children will
receive two copies of the

faulty gene and as a
result will be unable to

produce melanin.

119

THE BODY AT WORK

The science of genetics

but are protected from malaria too, allowing Repairing faulty genes Fertilised egg
them to pass the gene on to their children.
We reveal how donated cells can be used to mend A fertilised human egg is a
Genetics is a complex and rapidly evolving any damaged genes within the human body source of undifferentiated
field and more information about the function
of DNA is being discovered all the time. It is now Target gene stem cells, which can
known that environmental influences can alter become any type of cell.
the way that DNA is packaged in the cell, The healthy gene is
restricting access to some genes and altering isolated from the DNA
protein expression patterns. Known as of the donor individual.
epigenetics, these modifications do not actually
alter the underlying DNA sequence, but Packaging
regulate how it is accessed and used by the cell.
Epigenetic changes can be passed on from one The gene is
cell to its offspring, and thus provide an packaged into a
additional mechanism by which genetic delivery vector,
information can be modified across generations like a virus, to
of humans. help it get inside
the target cell.

Embryonic Transduction
stem cells
The new gene is introduced
The fertilised egg into the stem cells produced
becomes a blastocyst, by the fertilised egg.
which contains
When our genes undifferentiated Transplant
go wrong… embryonic stem cells.
The new cells are transplanted
Cancer is not just the result of one or two genetic Differentiation into the recipient, carrying with
mutations – in fact, it takes a whole series of them the healthy gene.
mistakes for a tumour to form. Cells contain Chemical signals are
oncogenes and tumour suppressor genes, whose added to the stem cells to
healthy function is to tell the cell when it should force them to differentiate
and should not divide. If these become damaged, into the desired cell type,
the cell cannot switch off its cell division eg liver cells.
programme and it will keep making copies of
itself indefinitely. Each time a cell divides there is
a risk that it will make a mistake when copying its
DNA, and gradually the cell makes more and more
errors, accumulating mutations that allow the
tumour to progress into malignant cancer.

How tumours develop

Tumour-associated Mutagens Localised Invasion Metastasis © SPL; Alamy; Thinkstock
genes
Environmental factors, or Cancer usually starts with just As the tumour grows in Further mutations allow cells
Genes normally involved in mutagens – such as radiation one or a few mutated cells; size it starts to invade of the tumour to break free and
regulating cell behaviour can and chemicals – can cause these begin to divide the surrounding area, enter the bloodstream. From
go on to cause cancer if they damage to the DNA, leading to uncontrollably in their local taking over here they can be distributed
become mutated. mutations in key genes. area creating a tumour. neighbouring tissues. throughout the body.

120

DID YOU KNOW? Approximately 300,000 people die from burns each year worldwide

What happens when
we burn ourselves?

Burns range from irritating to life-threatening
– learn about the different types now

Most people associate burns with red skin, but without large blisters. Only the no sensation. The basal growth layer is
flames, but they have many other epidermis is damaged, so regrowth is fast. destroyed so no new skin can grow.
causes. A burn is medically defined Second-degree burns (partial thickness) can be
as ‘coagulative destruction’ of skin, either superficial or deep. The skin usually Even minor burns can cause problems if not
meaning any energy source can cause one. This blisters and can be very painful. The dermis treated properly. The first priority is to stop the
energy damages underlying skin proteins and layer is also damaged so regrowth is slow, burning process; cold running water is often
fat cells, causing breaks in the skin. taking several weeks or even months. In the best first treatment. Infection, dehydration
Burns are generally classified by their depth. third-degree burns (full thickness) the skin is and protein loss are all problems that occur
First-degree (superficial) burns leave painful, left white or pale, with no blistering and little to next, which our resilient skin can solve itself if
the injury isn’t too severe.

How burns are measured

Classified by their depth, each burn case requires unique treatment

1
5

24
3

6

1 The skin 3 First-degree burn 5 Blisters

Your skin is vital to your wellbeing. It has multiple Only the uppermost skin layers (known as the epidermis) Blisters appear when the epidermis separates from the
important functions, including temperature control, are affected, but the burn is painful, leaving the area red, dermis, and are especially common in first and
sensation and appearance. raw and tender to the touch. second-degree burns.

2 Basal layer 4 Second-degree burn 6 Third-degree burn

This layer is the key to regeneration, as new skin cells These partial-thickness burns affect the upper or deep Deep burns destroy the basal layer and nerve endings, so
grow from here. If undamaged, regrowth occurs without dermal layers, and like first-degree burns hurt a lot they are painless. Regrowth will not occur alone, so skin
any need for medical assistance. because the nerve endings remain active. grafts are needed.

Four major causes of burns A second-degree burn will
heal itself over time but
Thermal Chemical Radiation Electrical probably leave scars

Heat can come from Alkalis burn for hours, Ionising radiation These often cause © Thinkstock
a flame or friction whereas acids are burns can be cover the deep burns that heal
(known as dry short-lived. These body due to exposure. slowly. A small skin
burns), hot liquids require no heat to Sunburn is a common defect may mask
(known as wet cause a burn, and can type of radiation burn, underlying damage,
burns) or contact take time to develop caused by exposure to which can extend
with hot surfaces. after skin contact. UV in sunlight. throughout the body.

121

THE BODY AT WORK Most of the amyloid
consisted of acellular pink
Blood vessels
globules that effaced and
Bvelososdels expanded the node, but
this image shows the

characteristic involvement
of blood vessel walls

Arteries and veins form the plumbing system of the human © Ed Uthman, MD
body, carrying blood through a complex system of different
sized and shaped pipes. We find out how they work…

The network of blood vessels in the two varieties; oxygen-rich (oxygenated) blood is like small back-roads connecting motorways to
human body must cope with different what the body uses for energy, and is bright red. dual carriageways.
volumes of blood travelling at different After it has been used, this oxygen-depleted
pressures. These blood vessels come (deoxygenated) blood is returned for recycling and is Arteries and veins are constructed differently to
in a multitude of different sizes and shapes, from dark red (not blue, as is often thought). cope with the varying pressures, but work in perfect
the large, elastic aorta down to very tiny, one-cell- tandem to ensure that the blood reaches its final
thick capillaries. Blood is carried in vessels, of which there are destination correctly. However, sometimes things go
Blood is the ultimate multitasker. It carries oxygen two main different types – arteries and veins. wrong which can lead to certain medical problems:
for various tissues to use, nutrients to provide Arteries carry blood away from the heart and deal varicose veins from failing valves; deep vein
energy, removes waste products and even helps you with high pressures, and so have strong elastic thrombosis from blood clots blocking the deep
warm up or cool down. It also carries vital clotting walls. Veins carry blood back towards the heart and venous system; heart attacks from blocked arteries;
factors which stop us bleeding. Blood comes in just deal with lower pressures, so have thinner walls. and lastly life-threatening aneurysms from weak
Tiny capillaries connect arteries and veins together, artery walls.

Connective Capillary wall
tissue
Elastic layer Cell nucleus
Inner lining
Muscle
Outer
Valve protective Connecting it
all together
How do veins layer
work? Capillaries are the tiny vessels which
Muscle layer connect small arteries and veins together.
Veins carry low pressure blood. They Their walls are only one cell thick, so this is
contain numerous one-way valves which Arteries – under the perfect place to trade substances with
stop backwards flow of blood, which can pressure! surrounding tissues. Red blood cells
occur when pressure falls in-between within these capillaries trade water,
heartbeats. Blood flows through these Arteries cope with all of the pressure oxygen, carbon dioxide, nutrients, waste
valves towards the heart but cannot pass generated by the heart and deliver and even heat. Because these vessels are
back through them in the other direction. oxygen-rich blood to where it needs to be 24 only one cell wide, the cells have to line up
Valves can fail over time, especially in the hours a day. The walls of arteries contain to pass through.
legs. This leads to saggy, unsightly veins, elastic muscles, allowing them to stretch
known as varicose veins. and contract to cope with the wide changes
in pressure generated from the heart. Since
122 the pressure is high, valves are
unnecessary, unlike the low-pressure
venous system.

DID YOU KNOW? Vascular surgeons can bypass blocked arteries using either the patient’s own veins or synthetic grafts

Arteries HEAD AND A game of two halves
ARMS
All arteries carry blood away In human beings, the heart is a double body tissues (the systemic circulation).
from the heart. They carry Aorta pump, meaning that there are two sides The right side of the heart pumps
oxygenated blood, except to the circulatory system. The left side of deoxygenated blood towards the lungs, so
for the pulmonary artery, The aorta is an artery which the heart pumps oxygen and nutrient-rich it can pick up new oxygen molecules to be
which carries deoxygenated carries oxygenated blood to the blood to the brain, vital organs and other used again (the pulmonary circulation).
blood to the lungs.
body; it is the largest blood “Plasma carries all
Lungs vessel in the body and copes of the different
with the highest pressure blood. types of cells”
In the lungs, carbon dioxide
is expelled from the body
and is swapped for fresh
oxygen from the air. This
oxygen-rich blood takes on
a bright red colour.

LUNG HEART LUNG What’s in
LIVER blood?
Veins The left side
It’s only the iron in red blood cells which
All veins carry blood The left side of the heart make blood red – take these cells away and
to the heart. They pumps oxygenated blood what you’re left with is a watery yellowish
carry deoxygenated solution called plasma. Plasma carries all
blood, except for for the body to use. It of the different types of cells and also
the pulmonary vein, pumps directly into contains sugars, fats, proteins and salts.
which carries The main cell types are red blood cells
oxygenated blood arteries towards the brain (formed from iron and haemoglobin, which
back to the heart. and other body tissues. carries oxygen around the body), white
blood cells (which fight infection from
bacteria, viruses and fungi) and platelets
(tiny cell fragments which stop bleeding by
forming clots at the sites of any damage).

Blood vessels

Different shapes and sizes

The right KIDNEY Capillary sphincter muscles Capillary bed
side TRUNK
AND LEGS These tiny muscles can open and close, This is the capillary network that
The right side of the which can decrease or increase blood flow connects the two systems. Here,
heart pumps through a capillary bed. When muscles exchange of various substances
deoxygenated exercise, these muscles relax and blood occurs with surrounding tissues,
blood to the lungs, flow into the muscle increases. through the one-cell thick walls.
where blood
exchanges carbon Venule
dioxide for
fresh oxygen. Arteriole
Vein Artery
Capillaries
123
Tiny capillaries connect
arteries and veins
together. They allow
exchange of oxygen,
nutrients and waste in the
body’s organs and tissues.

THE BODY AT WORK

A look inside your blood

How your
blood works

The science behind the miraculous fluid
that feeds, heals and fights for your life

White blood cells

White blood cells, or leukocytes, are
the immune system’s best weapon,
searching out and destroying
bacteria and producing antibodies
against viruses. There are five
different types of white blood cells,
all with distinct functions.

Platelet

When activated, these sticky cell
fragments are essential to the
clotting process. Platelets adhere to a
wound opening to stem the flow of
blood, then they team with a protein
called fibrinogen to weave tiny
threads that trap blood cells.

Red blood cell

Known as erythrocytes, red blood
cells are the body’s delivery service,
shuttling oxygen from the lungs to
living cells throughout the body and
returning carbon dioxide as waste.

Blood vessel wall Granulocyte © DK Images

Arteries and veins are composed of three The most numerous type of white
tissue layers, a combination of elastic blood cell, granulocytes patrol the
tissue, connective tissue and smooth bloodstream destroying invading
muscle fibres that contract under signals bacteria by engulfing and digesting
from the sympathetic nervous system. them, often dying in the process.

124

HEAD 1. Discovery of 2. First blood 3. Discovery of
veins and arteries transfusion
2HEAD “1818 - first human-to-blood types
In 300 BC, Greek anatomist After a century of animal-
LANDMARK Herophilus of Chalcedon figured human blood transfusions, In 1901, Austrian physician
BLOOD EVENTS out that arteries and veins James Blundell performed the
not only carry blood, but are first recorded human-to-human human transfusion”KarlLandsteinerwasthefirst
distinct pathways. transfusion in 1818.
to identify three basic blood
groups, revolutionising the
success of blood transfusions.

DID YOU KNOW? If you took all of the blood vessels out of your body and laid them end to end, they would stretch for 160,000km

Monocyte Components
of blood
The largest type of white blood cell, monocytes are born in bone
marrow, then circulate through the blood stream before maturing Blood is a mix of solids and liquids, a blend of highly specialised
into macrophages, predatory immune system cells that live in cells and particles suspended in a protein-rich fluid called
organ tissue and bone. plasma. Red blood cells dominate the mix, carrying oxygen to
living tissue and returning carbon dioxide to the lungs. For
every 600 red blood cells, there is a single white blood cell, of
which there are five different kinds. Cell fragments called
platelets use their irregular surface to cling to vessel walls and
initiate the clotting process.

54%
Plasma

1%

White blood
cellls and
platelets

45%

Red blood
cells

Bone marrow contributes
four per cent of a person’s

total weight

Plasma © Bobjgalindo

Composed of 92 per cent water, plasma is
the protein-salt solution in which blood
cells and particles travel through the
bloodstream. Plasma helps regulate

mineral exchange and pH, and carries the
proteins necessary for clotting.

“Red blood cells are so numerous
because they perform the most

essential function of blood”

Blood is the river of life. It watery current of plasma – a straw- deliver oxygen to every cell in the blood cells only live 120 days, the
feeds oxygen and coloured, protein-rich fluid – carrying body and carry away carbon dioxide. supply must be continuously
essential nutrients to billions of microscopic solids As an adult, all of your red blood cells replenished; roughly 2 million red
living cells and carries consisting of red blood cells, white are produced in red bone marrow, the blood cells are born every second.
away waste. It transports the foot blood cells and cell fragments called spongy tissue in the bulbous ends of
soldiers of the immune system, white platelets. The distribution is far from long bones and at the centre of flat A mature red blood cell has no
blood cells, which seek out and equal. Over half of blood is plasma, bones like hips and ribs. In the nucleus. The nucleus is spit out during
destroy invading bacteria and 45 per cent is red blood cells and a marrow, red blood cells start out as the final stages of the cell’s two-day
parasites. And it speeds platelets to tiny fragment, less than one per cent, undifferentiated stem cells called development before taking on the
the site of injury or tissue damage, is composed of white blood cells hemocytoblasts. If the body detects a shape of a concave, doughnut-like
triggering the body’s miraculous and platelets. minuscule drop in oxygen carrying disc. Like all cells, red blood cells are
process of self-repair. capacity, a hormone is released from mostly water, but 97 per cent of their
Blood looks like a thick, Red blood cells are so numerous the kidneys that triggers the stem cells solid matter is haemoglobin, a
homogenous fluid, but it’s more like a because they perform the most to become red blood cells. Because red complex protein that carries four
essential function of blood, which is to atoms of iron. Those iron atoms have

125

THE BODY AT WORK

A look inside your blood

Waste product 6. Reuse and recycle 1. Born in the bones 2. One life to live
of blood cell
As for the globin and other cellular When the body detects a low oxygen Mature red blood cells,
membranes, everything is carrying capacity, hormones released from also known as

converted back into basic amino the kidney trigger the production of new erythrocytes, are
acids, some of which will be used red blood cells inside red bone marrow. stripped of their nucleus

to create more red blood cells. in the final stages of
development, meaning

they can’t divide
to replicate.

Waste Life cycle of
excreted red blood cells
from body
Every second, roughly 2 million red blood cells decay and die. The
body is keenly sensitive to blood hypoxia – reduced oxygen

carrying capacity – and triggers the kidney to release a hormone
called erythropoietin. The hormone stimulates the production of

more red blood cells in bone marrow. Red blood cells enter the
bloodstream and circulate for 120 days before they begin to

degenerate and are swallowed up by roving macrophages in the
liver, spleen and lymph nodes. The macrophages extract iron from
the haemoglobin in the red blood cells and release it back into the
bloodstream, where it binds to a protein that carries it back to the

bone marrow, ready to be recycled in fresh red blood cells.

5. Iron ions 3. In circulation

In the belly of Kupffer cells, Red blood cells pass from
haemoglobin molecules are split into the bone marrow into the
heme and globin. Heme is broken bloodstream, where they
down further into bile and iron ions, circulate for around 120 days.
some of which are carried back and
stored in bone marrow.

4. Ingestion

Specialised white blood cells in the liver and
spleen called Kupffer cells prey on dying red blood
cells, ingesting them whole and breaking them
down into reusable components.

the ability to form loose, reversible red blood cells release their oxygen, another type of white blood cell, proteins and clotting factors found in
bonds with both oxygen and carbon they pick up carbon dioxide produce anti-bodies that build up our plasma, platelets weave a mesh of
dioxide – think of them as weak molecules, then course through the immunity to repeat intruders. And fibrin that stems blood loss and
magnets – making red blood cells such veins back toward the heart, where monocytes, the largest of the white triggers the formation of new collagen
an effective transport system for they are pumped back into the lungs blood cells, enter organ tissue and and skin cells.
respiratory gasses. Haemoglobin, to ‘exhale’ the excess CO2 and collect become macrophages, microbes that
which turns bright red when some more precious O2. ingest bad bacteria and help break But even these three functions of
oxygenated, is what gives blood its down dead red blood cells into blood – oxygen supplier, immune
characteristic colour. White blood cells are greatly reusable parts. system defender and wound healer –
outnumbered by red blood cells, but only begin to scratch the surface of the
To provide oxygen to every living they are critical to the function of the Platelets aren’t cells at all, but critical role of blood in each and every
cell, red blood cells must be pumped immune system. Most white blood fragments of much larger stem cells bodily process. When blood circulates
through the body’s circulatory system. cells are also produced in red bone found in bone marrow. In their resting through the small intestine, it absorbs
The right side of the heart pumps marrow, but white blood cells – unlike state, they look like smooth oval sugars from digested food, which are
CO2-heavy blood into the lungs, where red blood cells – come in five different plates, but when activated to form a transported to the liver to be stored as
it releases its waste gasses and picks varieties, each with its own clot they take on an irregular form energy. When blood passes through
up oxygen. The left side of the heart specialised immune function. The with many protruding arms called the kidneys, it is scrubbed of excess
then pumps the freshly oxygenated first three varieties, collectively called pseudopods. This shape helps them urea and salts, waste that will leave
blood out into the body through a granulocytes, engulf and digest stick to blood vessel walls and to each the body as urine. The proteins
system of arteries and capillaries, bacteria and parasites, and play a role other, forming a physical barrier transport vitamins, hormones,
some as narrow as a single cell. As the in allergic reactions. Lymphocytes, around wound sites. With the help of enzymes, sugar and electrolytes.

126

THE BLOOD PERCENTAGE
STATS
7% 7,000 litresOF BODY WEIGHT
BLOOD BLOOD PUMPED BY
HEART PER DAY

BLOOD IN

5 litres 2 millionHUMAN BODY
RED BLOOD CELLS
MADE EVERY SECOND

DID YOU KNOW? Until the 23rd week of foetal development, red blood cells are produced in the liver, not red bone marrow

Haemophilia “Platelets weave Thalassemia
a mesh of fibrin
This rare genetic blood disorder severely inhibits the that stems blood Another rare blood disorder affecting 100,000
clotting mechanism of blood, causing excessive loss” newborns worldwide each year, thalassemia
bleeding, internal bruising and joint problems. Platelets inhibits the production of haemoglobin, leading
are essential to the clotting and healing process, to severe anaemia. People who are born with the
producing threads of fibrin with help from proteins in most serious form of the disease, also called
the bloodstream called clotting factors. People who Cooley’s anaemia, suffer from enlarged hearts,
suffer from haemophilia – almost exclusively males – are livers and spleens, and brittle bones. The most
missing one of those clotting factors, making it difficult to effective treatment is frequent blood
seal off blood vessels after even minor injuries. transfusions, although a few lucky patients have
been cured through bone marrow transplants
from perfectly matching donors.

Sickle cell anaemia Blood Hemochromatosis
disorders
Anaemia is the name for any blood disorder that results One of the most common genetic
in a dangerously low red blood cell count. In sickle cell Blood is a delicate balancing act, with blood disorders, hemochromatosis is
anaemia, which afflicts one out of every 625 children of the body constantly regulating the medical term for “iron overload,”
African descent, red blood cells elongate into a sickle in which your body absorbs and
shape after releasing their oxygen. The sickle-shaped oxygen flow, iron content and clotting stores too much iron from food.
cells die prematurely, leading to anaemia, or sometimes ability. Unfortunately, there are Severity varies wildly,
lodge in blood vessels, causing terrible pain and even several genetic conditions and and many people experience few
organ damage. Interestingly, people who carry only one chronic illnesses that can disturb symptoms, but others suffer
gene for sickle cell anaemia are immune to malaria. the balance, sometimes with serious liver damage or
deadly consequences. scarring (cirrhosis), irregular
heartbeat, diabetes and even heart
Left to right: a red blood cell, failure. Symptoms can be aggravated
platelet and white blood cell by taking too much vitamin C.

© Science Photo Library Deep vein thrombosis

Thrombosis is the medical term for any blood clot that is
large enough to block a blood vessel. When a blood clot
forms in the large, deep veins of the upper thigh, it’s
called deep vein thrombosis. If such a clot breaks free, it
can circulate through the bloodstream, pass through
the heart and become lodged in arteries in the lung,
causing a pulmonary embolism. Such a blockage can
severely damage portions of the lungs, and multiple
embolisms can even be fatal.

Blood and healing More than a one-trick pony, your blood
is a vital cog in the healing process

Think of blood as the body’s

emergency response team to an STAGE 1 STAGE 2 STAGE 3 STAGE 4

injury. Platelets emit signals that HAEMOSTASIS

encourage blood vessels to Activated platelets aggregate
around the surface of the wound,
contract, stemming blood loss. stimulating vasoconstriction.
Platelets react with a protein in
The platelets then collect around plasma to form fibrin, a web-like
mesh of stringy tissue.
the wound, reacting with a

protein in plasma to form fibrin, a

tissue that weaves into a mesh.

Blood flow returns and white

blood cells begin their hunt for

bacteria. Fibroblasts create beds INJURY INFLAMMATORY STAGE PROLIFERATIVE STAGE

of fresh collagen and capillaries Whentheskinsurfaceiscut,torn Once the wound is capped with a Fibroblasts lay fresh layers of
drying clot, blood vessels open up collagen inside the wound and
to fuel skin cell growth. The scab orscrapeddeeplyenough,blood again, releasing plasma and white capillaries begin to supply blood
seeps from broken blood vessels to blood cells into the damaged for the forming of new skin cells.
begins to contract, pulling the fill the wound. To stem the flow of tissue. Macrophages digest Fibrin strands and collagen pull
harmful bacteria and dead cells. the sides of the wound together.
growing skin cells closer together bleeding,thebloodvesselsaround

until damaged tissue is replaced. thewoundconstrict.

127

THE BODY AT WORK

Controlling the human body

Hormones Hypothalamus

How the human endocrine system Releases hormones to the
develops and controls the human body pituitary gland to promote
its production and
secretion of hormones to
the rest of the body.

The glands in the endocrine system women. The majority of hormones are peptides Pituitary gland
use chemicals called hormones to that consist of short chains of amino acids.
communicate with and control the They are secreted by the pituitary and Releases hormones to
cells and organs in our bodies. parathyroid glands. Amine hormones are the male and female
They are ductless glands that secrete different secreted by the thyroid and adrenal medulla reproductive organs
types of hormone directly into the bloodstream and are related to the fight or flight response. and to the adrenal
and target specific organs. glands. Stimulates
The target organs contain hormone The changes that are caused by the growth in childhood and
receptors that respond to the chemical endocrine system act more slowly than the maintains adult bone
instructions supplied by the hormone. There nervous system as they regulate growth, and muscle mass.
are 50 different types of hormone in the body moods, metabolism, reproductive processes
and they consist of three basic types: peptides, and a relatively constant stable internal Pineal gland
amines and steroids. environment for the body (homeostasis). The
Steroids include the testosterone hormone. pituitary, thyroid and adrenal glands combine Secretes melatonin, which
This is secreted by the cortex of the adrenal to form the major elements of the body’s controls sleep patterns and
gland, the male and female reproductive endocrine system along with various other controls the production of
organs and by the placenta in pregnant elements such as the male testes, the female hormones related to the
ovaries and the pancreas. reproductive organs.

“Amine hormones are secreted by the
thyroid and adrenal medulla”

Adrenal gland The
endocrine
We have two adrenal glands that are positioned on top of both system © DK Images
kidneys. The triangular-shaped glands each consist of a two-
centimetre thick outer cortex that produces steroid hormones, Thymus
which include testosterone, cortisol and aldosterone.
Is part of the immune
The ellipsoid shaped, inner part of the gland is known as the system. It produces
medulla, which produces noradrenaline and adrenaline. These thymosins that control
hormones increase the heart rate, and the body’s levels of oxygen the behaviour of white
and glucose while reducing non-essential body functions. blood T-cells.

The adrenal gland is known as the ‘fight or flight’ gland as it Adrenal glands
controls how we respond to stressful situations, and prepares the
body for the demands of either fighting or running away as fast as Controls the burning of
you can. Prolonged stress over-loads this gland and causes illness. protein and fat, and
regulates blood pressure.
Medulla The medulla secretes
adrenaline to stimulate the
Cortex fight or flight response.

Kidney

Male testes

These two glands produce
testosterone that is
responsible for sperm
production, muscle and
bone mass and sex drive.

128

DID YOU KNOW? When you are excited the hypothalamus and pituitary gland release opiate-like endorphins

Hypothalamus Pituitary gland

Hypothalamus The pea-sized pituitary gland is a major production of sperm cells. The posterior
neurons endocrine gland that works under the lobe stores vasopressin and oxytocin that
control of the hypothalamus. The two is supplied by the hypothalamus.
These synthesise and organs inside the brain work in concert and Vasopressin allows the retention of water in
send hormones to the mediate feedback loops in the endocrine the kidneys and suppresses the need to
posterior lobe. system to maintain control and stability excrete urine. It also raises blood pressure
within the body. by contracting the blood vessels in the heart
Portal veins and lungs.
The pituitary gland features an anterior
Hormones from the (front) lobe and a posterior (rear) lobe. The Oxytocin influences the dilation of the
hypothalamus are anterior lobe secretes growth hormones cervix before giving birth and the
carried to the that stimulate the development of the contraction of the uterus after birth. The
anterior lobe muscles and bones; it also stimulates the lactation of the mammary glands are
through these veins. development of ovarian follicles in the stimulated by oxytocin when mothers begin
female ovary. In males, it stimulates the to breastfeed.
Anterior lobe

Posterior lobe

Parathyroid Thyroid and parathyroids

Works in combination Thyroid cartilage The two lobes of the thyroid sit on each side of the
with the thyroid to (Adam’s apple) windpipe and are linked together by the isthmus that
control levels of calcium. runs in front of the windpipe. It stimulates the amount
REAR of body oxygen and energy consumption, thereby
Thyroid FRONT keeping the metabolic rate of the body at the current
Trachea levels to keep you healthy and active.
Important for maintaining Right (windpipe)
the metabolism of the lobe Parathyroids The hypothalamus and the anterior pituitary gland
body. It releases T3 and are in overall control of the thyroid and they respond to
T4 hormones to control Left changes in the body by either suppressing or increasing
the breakdown of food lobe thyroid stimulating hormones. Overactive thyroids
and store it, or release it cause excessive sweating, weight loss and sensitivity to
as energy. heat, whereas underactive thyroids cause sensitivity to
hot and cold, baldness and weight gain. The thyroid can
Isthmus swell during puberty and pregnancy or due to viral
infections or lack of iodine in a person’s diet.

The four small parathyroids regulate the calcium
levels in the body; it releases hormones when calcium
levels are low. If the level of calcium is too high the
thyroid releases calcitonin to reduce it. Therefore, the
thyroid and parathyroids work in tandem.

Pancreas Pancreatic cells Isletsof Red blood Acinar cells
Langerhans cells
Maintains healthy These secrete
blood sugar levels in The pancreas is positioned in the abdominal cavity above the small digestive enzymes
the blood stream. intestine. It consists of two types of cell, the exocrine cells that do not
secrete their output into the bloodstream but the endocrine cells do. to the intestine.
Female ovaries
The endocrine cells are contained in clusters called the islets of
Are stimulated by Langerhans. They number approximately 1 million cells and
hormones from the are only one or two per cent of the total number of cells in
pituitary gland and the pancreas. There are four types of endocrine cells in
control the the pancreas. The beta cells secrete insulin and the
menstrual cycle. alpha cells secrete glucagon, both of which
stimulate the production of blood sugar (glucose)
in the body. If the Beta cells die or are destroyed Duct cells
it causes type 1 diabetes, which is fatal unless
treated with insulin injections. Secrete bicarbonate
to the intestine.
The other two cells are the gamma and
delta cells. The former reduces appetite
and the latter reduces the absorption of food
in the intestine.

129

THE BODY AT WORK

Human urinary system

How does the
body filter
waste?
Kidneys

This is where liquids are
filtered and nutrients are
absorbed before urine

exits into the ureters.

Every day the body produces waste
products that enter the bloodstream –
but how do we get rid of them?

The human urinary system’s water levels in the body, sodium and Ureter
primary function is to remove potassium levels among other electrolytes,
by-products which remain in blood pressure, pH of the blood and are These tubes link the
the blood after the body has also involved in red blood cell production kidneys and the bladder.
metabolised food. The process is made up through the creation and release of the
of several different key features. Generally, hormone erythropoietin. Consequently, Inferior vena cava
this system consists of two kidneys, two they are absolutely crucial to optimum
ureters, the bladder, two sphincter body operation. This carries deoxygenated
muscles (one internal, one external) and a blood back from the kidneys
urethra and these work alongside the After blood has been filtered by the to the right aorta of the heart.
intestines, lungs and skin, all of which kidneys, the waste products then travel
excrete waste products from the body. down the ureters to the bladder. The Abdominal aorta
The abdominal aorta is an important bladder’s walls expand out to hold the
artery to the system as this feeds the renal urine until the body can excrete the waste This artery supplies blood
artery and vein, which supply the kidneys out through the urethra. The internal and to the kidneys, via the renal
with blood. This blood is filtered by the external sphincters then control the artery and vein. This blood
kidneys to remove waste products, such as release of urine. is then cleansed by
urea which is formed through amino acid the kidneys.
metabolism. Through communication Generally, a human will produce
with other areas of the body, such as the approximately 2.5-3 litres of urine a day, Bladder
hypothalamus, the kidneys also control although this can vary dramatically
dependant on external factors such as This is where urine
water consumption. gathers after being
passed down the
ureters from
the kidneys.

“Generally, a human will produce
2.5-3 litres of urine a day”

How do the kidneys work?

The kidneys will have around 150-180 litres of blood to filter per day, but only pass around
two litres of waste down the ureters to the bladder for excretion, therefore the kidneys
return much of this blood, minus most of the waste products, to the heart for re-
oxygenation and recirculation around the body.

The way the kidneys do this is to pass the blood through a small filtering unit called a
nephron. Each kidney has around a million of these, which are made up of a number of
small blood capillaries and a tube called the renal tubule. The blood capillaries sift the
normal cells and proteins from the blood for recirculation and then direct the waste
products into the renal tubule. This waste, which will primarily consist of urea, mixes with
water and forms urine as it passes through the renal tubule and then into the ureter on its
way to the bladder.

130

STHTAETS 1H-8uhmrsan fist 15400–01–8600li0trmeslURINARYSYSTEM
AVERAGE SIZE BLADDER
OF KIDNEY CAPACITY
TIME URINE’S BLOOD FILTERED
IN BLADDER PER DAY

DID YOU KNOW? On average, you make the same amount of urine in the day as in the night

How do we store waste until
we’re ready to expel it?

The bladder stores waste products by allowing the urine to enter
through the ureter valves, which attach the ureter to the bladder.
The walls relax as urine enters and this allows the bladder to
stretch. When the bladder becomes full, the nerves in the bladder
communicate with the brain and cause the individual to feel the
urge to urinate. The internal and external sphincters will then
relax, allowing urine to pass down the urethra.

Bladder 1. Ureters
fills
These tubes connect to the kidneys and urine
flows down to the bladder through them.

Why do we 2. Internal urethral sphincter
get thirsty?
This remains closed to ensure urine does
Maintaining the balance between the not escape unexpectedly.
minerals and salts in our body and water is
very important. When this is out of balance, 3. External 5. Bladder walls
the body tells us to consume more liquids to urethral (controlled by
redress this imbalance in order for the body sphincter
to continue operating effectively. detrusor muscles)
This secondary
This craving, or thirst, can be caused by sphincter also The detrusor muscles in the wall of
too high a concentration of salts in the body, remains closed
or by the water volume in the body dropping to ensure no the bladder relax to allow expansion
too low for optimal operation. Avoiding urine escapes.
dehydration is important as long term of the bladder as necessary.
dehydration can cause renal failure, among 4. Ureter valves
other conditions.
These valves are situated
The human at the end of the ureters
urinary and let urine in.
system
Bladder 1. Internal urethral sphincter
Renal artery and vein empties
This relaxes when the body is ready to expel
This supplies blood to the kidneys the waste.
in order for them to operate, and
then removes deoxygenated blood 2. External
urethral sphincter
after use by the kidneys.
This also relaxes for the urine
Pelvis to exit the body.

The bladder sits in the pelvis, 3. Bladder
and the urethra passes through walls
(controlled
it for urine to exit the body. by detrusor
muscles)
Urethra
These muscles
The urethra is the tube
that urine travels contract to force

through to exit the body. the urine out of

© DK Images the bladder. 4. Urethra

Urine travels down this
passageway to exit the body.

131

THE BODY AT WORK

Tracheotomies

Tracheotomy surgery

Discover the science and tech behind this life-saving procedure

If the upper airway is blocked, by Anatomy of a tracheotomy
trauma, cancer or inflammation, an
alternative route must be found for The trachea is surrounded by a minefield of major
air to enter the lungs. blood vessels, nerves, glands and muscles
Planned tracheotomies are performed under
general anaesthesia or sedation. The neck is Larynx Thyroid cartilage
extended backwards to allow the surgeon to
easily identify the structures in the throat and The vocal cords sit The surgeon uses the
to make an accurate incision (see diagram). behind the thyroid prominent Adam’s apple as
First, a vertical cut is made in the skin, below cartilage, above the a marker to locate the best
the tracheal cartilage, and the underlying point of the incision. incision site on the neck.
muscle and blood vessels are carefully moved
out of the way to expose the trachea. Cartilage ring Oesophagus
The trachea is normally held open by
C-shaped rings of cartilage, which prevent the The trachea is held open The oesophagus lies
airway from collapsing. A hole is made between by stiff C-shaped rings behind the trachea, so the
the third and fourth rings, allowing the surgeon made of cartilage. surgeon must take care
access to the airway without disrupting the not to puncture through
cartilage supports. A tracheotomy tube is then Stoma from one to the other.
inserted into the airway and secured to the
neck. If the tracheal opening is going to be a A temporary or Trachea
permanent feature rather than temporary then permanent tube is
a piece of cartilage may be removed to allow the inserted into the The trachea connects the
tube to sit more comfortably. trachea through an lungs to the mouth and
The vocal cords sit just behind the tracheal incision between the nose; a tracheotomy
cartilage, above the tracheotomy incision site, rings of cartilage. bypasses them to grant
but in order to talk, air must be able to pass direct access to the lungs.
through the vocal cords to make them vibrate. Flanges
Some tracheotomy tubes contain unidirectional Carotid artery
valves, enabling the patient to breathe in The outer portion of
through the tube and out through their mouth, the tube has flanged Large arteries supplying blood
which provides good air supply to the lungs, edges, which means it to the brain and face run up
without hampering speech. can be securely taped either side of the trachea.
If the patient is unable to breathe unaided, a to the neck.
ventilator may be attached to mechanically Thyroid
move air in and out of the lungs.
The thyroid gland,
Have you got a pen? responsible for making
numerous hormones,
A tracheotomy is a complex procedure, so in sits just beneath the
life-threatening, emergency situations a faster tracheotomy site.
procedure – known as a cricothyrotomy (also
called cricothyroidotomy) – may be performed. © Corbis
A higher incision is made just below the thyroid
cartilage (Adam’s apple) and then through the
cricothyroid membrane, directly into the trachea.

It is possible to perform this procedure with a
sharp instrument and any hollow tube, such as a
straw or a ballpoint pen case. However, finding
the correct location to make the incision is
challenging, and without medical training there
is great risk of damaging major blood vessels,
the oesophagus or the vocal cords.

132

STRANGE Where did hay fever get Answer:
BUT TRUE its name?
The term hay fever has nothing to do with hay, and
MISLEADING NAME A Hay allergy B Harvesting C Doctor’s name everything to do with trees, grasses and ragweed.
The name came about because symptons would
strike during hay-harvesting season, when these
pollens would be rife.

DID YOU KNOW? Allergic diseases, including asthma, are the fifth most common chronic disease in all ages

When hay fever attacks

When summer strikes, why do some of us suffer?

We trample on lawns and mow headaches from blocked sinuses or coughing Pollen forecast
them down, but eventually grass caused by mucus dripping down the back of the
gets revenge. Its pollen causes throat from the nose. GRASS POLLEN
many of us to suffer from hay fever, (MAY-JULY)
and so do trees, weeds and even some fruit. People genetically predisposed to hay fever
Despite being smaller than the tip of a pin, are called atopics. Hay fever usually develops 95 per cent of hay-fever sufferers are
during childhood or teenage years, but adults allergic to grass pollen. Close
windows on dry, windy days.

pollen is carried by the wind and lodges in the can get it too. This is likely to follow repeated TREE POLLEN (MARCH-MAY)

nasal lining tissues and throat, where it can contact with a substance that your immune Affects 25 per cent of sufferers and
cause an allergic reaction. This is when the system perceives as a threat. No one knows for instigators include ash, birch, beech,
body mistakenly thinks it has been invaded by sure why hay fever starts affecting someone at willow and oak. Cut back branches in
the garden to reduce pollen.

a threat, such as a virus. the point in time it does. WEED POLLEN (SUMMER -
To fight back, the body produces a type of Hay-fever sufferers are in trouble when the EARLY AUTUMN)

antibody known as immunoglobulin E (IgE) in pollen count reaches 50 pollen grains per cubic In the USA, ragweed is the biggest
response to the allergen, causing nasal metre of air. You’ll experience it worse in the culprit. One plant can spew out
passages to become inflamed, producing more morning when plants release their pollen. millions of pollen grains daily.

mucus. This is designed to help flush out the Allergens collect in the air on humid days and

allergens but can lead to other symptoms like during storms, but rain clears the pollen. Too much histamine

Why do we get a runny nose? Histamine irritates the upper
respiratory passages, making
An inside look at how pollen Airborne pollen them swell and produce the
can affect us typical hay fever symptoms.
Fine dusty pollen is carried Histamine makes your mucus
The statistics… by the wind and inhaled membranes work over time,
through the nasal passage. producing enough mucus to
Allergy in numbers People with a genetic flush the pollen out.
disposition to hay fever,
15%: Of UK population get known as atopics, will have
hay fever an allergic reaction.

40%: Risk if one parent suffers

80%: Risk if both parents suffer

95%: Of hay-fever sufferers are Antibodies
allergic to grass pollen
The pollen protein triggers
1 in 5: Affected by hay fever your immune system,
which creates thousands
21 million: UK adults suffer of antibodies. The
from one or more antibodies attach
type of allergy themselves to mast cells,
which release histamine
– a substance the body
produces to fight infection.

Protein problem 133

Proteins on the surface of the
pollen grain irritate and
inflame the cells that line your
mouth, nose, eyes and throat.
The body’s immune system
treats the pollen like a virus
and takes action to expel it.

THE BODY AT WORK

The sensory system

Ears feed About 100 million
sounds to the photoreceptors
brain but also
control balance per eye

9,000 taste We can process
buds over over 10,000
the tongue
and throat different smells

Touch is the
first sense
to develop in
the womb

Exploring the
sensory system

The complex senses of the human body and how
they interact is vital to the way we live day to day

The sensory system is what enables us There are thousands of different stimuli that can can cause excruciating pain; this particular
to experience the world. It can also trigger our senses, including light, heat, chemicals condition is known as phantom limb syndrome.
warn us of danger, trigger memories in food and pressure. These ‘stimulus modalities’
and protect us from damaging stimuli, are then detected by specialised receptors, which However the sensory system is able to adapt to
such as hot surfaces. The sensory system is highly convert them into sensations such as hot and cold, change, with the loss of one often leading to others
developed, with many components detecting both tastes, images and touch. The incredible receptors being heightened. Our senses normally function to
physical and emotional properties of the – like the eyes, ears, nose, tongue and skin – have gently inhibit each other in order to moderate
environment. For example, it can interpret adapted over time to work seamlessly together individual sensations. The loss of sight from
chemical molecules in the air into smells, moving and without having to be actively ‘switched on’. blindness is thought to lead to strengthening of
molecules of sound into noises and pressure signals from the ears, nose and tongue. Having
placed on the skin into touch. Indeed, some of our However, sometimes the sensory system can go said this, it’s certainly not universal among the
senses are so finely tuned they allow reactions wrong. There are hundreds of diseases of the blind, being more common in people who have
within milliseconds of detecting a new sensation. senses, which can have both minor effects, or a been blind since a young age or from birth.
The five classic senses are sight, hearing, smell, life-changing impact. For example, a blocked ear Similarly, some people who listen to music like to
taste and touch. We need senses not only to can affect your balance, or a cold your ability to close their eyes, as they claim the loss of visual
interpret the world around us, but also to function smell – but these things don’t last for long. input can enhance the audio experience.
within it. Our senses enable us to modify our
movements and thoughts, and sometimes they In contrast, say, after a car accident severing the Although the human sensory system is well
directly feed signals into muscles. The sensory spinal cord, the damage can be permanent. There developed, many animals out-perform us. For
nervous system that lies behind this is made up of are some very specific problems that the sensory example, dogs can hear much higher-pitched
receptors, nerves and dedicated parts of the brain. system can bring as well. After an amputation, the sounds, while sharks have a far better sense of
brain can still detect signals from the nerves that smell – in fact, they can sniff out a single drop of
used to connect to the lost limb. These sensations blood in a million drops of water!

134

STRANGE Which creatures can have Answer:
BUT TRUE up to a hundred eyes?
Scallops are an underwater mollusc that
SIGHT TO BEHOLD A Scallops B Spiders C Peacocks amazingly can have as many as 100 eyes!
Although they can’t create as clear a picture as
our eyes, they can detect enough light and
movement to warn them of oncoming predators.

DID YOU KNOW? Taste and smell are closely linked. To test this, pinch your nose as you eat something and it will taste bland

Body’s messengers Retinal neuron Olfactory neuron

The sensory system is formed from neurons. These are These retinal bipolar cells are found in The many fine dendritic arms
specialised nerve cells which transmit signals from one the eye, transmitting light signals from of the olfactory cell line the
end to the other – for example, from your skin to your the rods and cones (where light is inner surface of the nasal
brain. They are excitable, meaning that when detected) to the ganglion cells, which cavity and detect thousands of
stimulated to a certain electrical/chemical threshold send impulses into the brain. different smells, or odorants.
they will fire a signal. There are many different types,
and they can interconnect to affect each other’s signals.

Motor neuron Purkinje cell Anaxonic neuron

These fire impulses These are the largest neurons Found within the retina of the
from the brain to the body’s in the brain and their many eye, these cells lack an axon
muscles, causing contraction dendritic arms form multiple (nerve fibre) and allow rapid
and thus movement. They connections. They can both modification of light signals
have lots of extensions (ie excite and inhibit movement. to and from bipolar cells.
they are multipolar) to
spread the message rapidly. Pyramidal neuron

Unipolar neuron These neurons have a
triangular cell body, and
These sensory neurons were thus named after
transduce a physical pyramids. They help
stimulus (for example, when to connect motor
you are touched) into an neurons together.
electrical impulse.
Olfactory nerve
How do we smell?
New signals are rapidly
Find out how our nose transmitted via the
and brain work together
to distinguish scents olfactory nerve to the brain,
which collates the data
Olfactory bulb with sight and taste.

Containing many types of Cribriform plate Total recall
cell, olfactory neurons
branch out of here through A bony layer of the skull Have you ever smelt something that
the cribriform plate below. with many tiny holes, transported you back in time? This is
known as the Madeleine effect because
Olfactory neuron which allow the fibres of the writer Marcel Proust once described
the olfactory nerves to how the scent of a madeleine cake
These neurons are highly suddenly evoked strong memories and
adapted to detect a wide pass from nose to brain. emotions from his childhood.
range of different odours.
The opposite type of recall is
Olfactory voluntary memory, where you actively
epithelium try and remember a certain event.
Involuntary memories are intertwined
Lining the nasal cavity, this with emotion and so are often the more
layer contains the long intense of the two. Younger children
extensions of the olfactory under the age of ten have stronger
neurons and is where involuntary memory capabilities than
chemical molecules in air older people, which is why these
trigger an electric impulse. memories thrust you back to childhood.
Older children use voluntary memory
more often, eg when revising for exams.

135

THE BODY AT WORK

The sensory system

Key nerves

These transmit vital sensory information
to our brain while also sending motor
function signals all around the body

Olfactory nerve

Starting in the nose, this nerve
converts chemical molecules
into electrical signals that are
interpreted as distinct odours
via chemoreceptors.

Understanding Eye movements Optic nerve
lightning reflexes
The trochlear, abducent The optic nerves convert light signals
Have you ever felt something scorching hot or and oculomotor nerves into electrical impulses, which are
freezing cold, and pulled your hand away without control the eye muscles interpreted in the occipital lobe at the
even thinking about it? This reaction is a reflex. and so the direction in back of the brain. The resulting image
Your reflexes are the most vital and fastest of all which we look. is seen upside down and back to front,
your senses. They are carried out by the many but the brain reorients the image.
‘reflex arcs’ located throughout the body.
Trigeminal nerve
For example, a temperature-detecting nerve in
your finger connects to a motor nerve in your This nerve is an example of a
spine, which travels straight to your biceps, mechanoreceptor, as it fires when
creating a circular arc of nerves. By only having your face is touched. It is split into
two nerves in the circuit, the speed of the reflex three parts, covering the top, middle
is as fast as possible. A third nerve transmits the and bottom thirds of your face.
sensation to the brain, so you know what’s
happened, but this nerve doesn’t interfere with
the arc; it’s for your information only. There are
other reflex arcs located within your joints, so
that, say, if your knee gives way or you suddenly
lose balance, you can compensate quickly.

1. Touch receptor

When a touch receptor is
activated, information about the
stimulus is sent to the spinal cord.
Reflex actions, which don’t
involve the brain, produce rapid
reactions to dangerous stimuli.

Facial and
trigeminal motors

The motor parts of these

nerves control the muscles of

facial expression (for

example, when you smile),

and the muscles of the

jaw to help you chew.

2. Signal sent 3. Motor neurons
to spine feed back

When sensory nerve The signals trigger motor

endings fire, neurons that initiate their

information passes own impulses that feed back

through nerve fibres to the muscle, telling it to

to the spinal cord. move the body part.

136

5FATCOTPS A matter of taste Smell vs sight Sensitive skin Upside down Staying steady

HUMAN SENSES 1 There are about 9,000 taste 2 Odours offer better memory 3 Human skin contains over half 4 The images formed in the 5 Ears do more than detect
buds on the tongue and throat. recall than visual cues, as smell a million sensory receptors. occipital cortex are upside sound. The fluid and fine hairs
These convert chemicals found is tied to emotion. Looking at These are of the highest down, before the brain flips in the inner ear maintain
in saliva into electrical signals, an old photograph can trigger concentration in the fingertips, them. However babies start balance. If you spin round and
split into five tastes: sweet, salt, memory, but a smell can evoke the ends of the toes and lips, by seeing upside down, until stop, this fluid is still moving
sour, bitter and umami. how you felt at the time. where they’re most needed. the brain learns to adapt. which is why we get dizzy.

DID YOU KNOW? The three smallest bones in the human body – the hammer, anvil and stirrup – are located in the middle ear

Intermediate nerve Crossed senses

This is a small part of the larger Vestibulocochlear Synaesthesia is a fascinating, if yet completely
facial nerve. It provides the key nerve understood, condition. In some people, two or
sensation to the forward part of more of the five senses become completely
the tongue to help during eating. This nerve provides linked so when a single sensation is triggered, all
sensation to the inner part the linked sensations are activated too. For
example, the letter ‘A’ might always appear red,
of the ear. or seeing the number ‘1’ might trigger the taste
of apples. Sights take on smells, a conversation
Glossopharyngeal motor can take on tastes and music can feel textured.

The motor part of this nerve controls People with synaesthesia certainly don’t
the pharynx, helping us consider it to be a disorder or a disease. In fact,
many do not think what they sense is unusual,
to speak and breathe normally. and they couldn’t imagine living without it. It
often runs in families and may be more common
than we think. More information about the
condition is available from the UK Synaesthesia
Association (www.uksynaesthesia.com).

55 5 5 5 5 55 5 5 5 5
55 5 55 5

5 5 5 25 5 5 5 25

5 5 5 25 2 5 5 5 25 2

5 52 22 5 52 2 2
5 5

555 5 5 555 5 5

Non-synaesthetes But a synaesthete who
struggle to identify a sees 2s as red and 5s
triangle of 2s among a as green can quickly
field of number 5s. pick out the triangle.

A patient’s sense of proprioception
is being put to the test here

Vagus nerve Vagus motor Is there really a © SPL; Alamy; Thinkstock
‘sixth sense’?
The vagus nerve is spread all This portion of the vagus
around the body. It is a mixed nerve can slow the Our sense of balance and the position of our
sensory and motor nerve, and bodies in space are sensations we rarely think
is responsible for controlling all heartbeat and breathing about and so are sometimes thought of as a
of the functions we don’t think rate, or increase the ‘sixth sense’. There is a whole science behind
about – like our heartbeat. speed of digestion. them though, and they are collectively called
proprioception. There are nerves located
The hypoglossal nerve Accessory nerve throughout the musculoskeletal system (for
example, within your muscles, tendons,
This nerve controls the Connecting the muscles of the neck ligaments and joints) whose job it is to send
movements of the tongue. to the brain, this nerve lets us turn information on balance and posture back to the
our heads from side to side. brain. The brain then interprets this information
rapidly and sends instructions back to the
muscles to allow for fine adjustments in balance.
Since you don’t have to think about it and you
can’t switch it off, you don’t know how vital
these systems are until they’re damaged. Sadly
some medical conditions, including strokes, can
affect our sense of proprioception, making it
difficult to stand, walk, talk and move our limbs.

137

THE BODY AT WORK

Chickenpox

Understanding
chickenpox

Discover the biology behind the infamous childhood
ailment and why it never really goes away…

Chickenpox is a strain of the face, arms, legs, stomach and back. These weak immune system or be particularly
Varicella zoster virus, which many develop into fluid-filled blisters and are often vulnerable to the disease.
of us have experienced during our accompanied by a fever. The blisters burst, scab
youth. Most prominent in children, over and fall off within a few days, but new After the outbreak, chickenpox doesn’t
the virus is contracted through coughing and waves of spots can emerge to replace them; it disappear entirely. The disease lies in a
sneezing or transferred on shared objects, usually takes one to two weeks for the body to dormant state within the body as your immune
which makes schools a prime location. regain control. Chickenpox is rarely serious but system keeps it under wraps. The infection can
The most famous symptom is the appearance it is important not to interfere with the scabs as break out again later and reappear as shingles.
of small itchy red spots, which vary in size from infection can make it more severe. A rash builds up on a certain point of the body
10-20 millimetres (0.4-0.8 inches) across. The and the symptoms return, most commonly in
extent can vary but in most cases they cover the A vaccine is only offered in extreme people over 50. On average, three in every 1,000
circumstances when an individual may have a people contract shingles in the UK each year.

When chickenpox strikes back… Blisters emerge Grown-up © Alamy; Thinkstock
chickenpox
Get under the skin to see how shingles can catch the body unawares Blisters become visible and
inflamed rashes appear on 90 per cent of adults are immune
Start of the illness all affected areas. if they’ve had the disease as a
child but it still affects adults and
The virus infiltrates the Don’t scratch! teenagers. If you develop
skin and causes chickenpox at a later age, all the
inflammation and a The blisters then symptoms are more severe, with
burning sensation. harden into scabs and more chronic pain, headaches and
fall off. Scratching at sore throats; therefore, there is
Low immunity the spots makes the greater need for treatment, such
healing process slower. as pain relief and soothing creams.
The Varicella virus
becomes active Future effects The disease tends to affect
when the immune adults more dramatically as it can
system is weak, In around 10-20 per now mutate into a variety of other
overcoming the cent of people who strains, such as shingles or, in
body’s natural have shingles, the extreme cases, lead to
defences. nerve fibres become encephalitis, postherpetic
damaged which can neuralgia or pneumonia. However,
Dormancy lead to postherpetic the chances of this happening are
neuralgia (nerve pain). only around ten per cent.
Once the immune system regains
control, the virus retreats and lies Deaths from chickenpox
dormant in the body’s nervous have reduced dramatically
system, but it can return later. in the last 25 years

138

5 TOP Runny noses Hush, little baby Onion weeping Crocodile tears Darwin’s discovery
FACTS
1 If you find that your nose runs a 2 Babies typically cry for about 3 Syn-propanethial-S-oxide is 4 While crocodiles are known for 5 There is a condition called the
CRYING lot when you cry, it is because one to three hours per day. This created by an enzyme in a cut looking teary as they eat food PseudoBulbar Affect (PBA) in
excess tears are running from can be for a variety of reasons, onion. When it evaporates, this they’ve just caught, they aren’t which people cry or laugh
your eyes, down your tear ducts because they’re hungry, thirsty, compound irritates our lacrimal sad. The tears merely lubricate uncontrollably. First described by
and into your nose, causing tired, scared or have just been to glands and tears are triggered in their eyes when they spend time Charles Darwin it is often the result
those tearful sniffles. the toilet. order to dilute it. out of the water. of brain injuries.

DID YOU KNOW? The average person will produce 140-280g (5-10oz) of basal tears per day to keep the eyes moist

Why do we cry?

Find out how our tears have been helping to
protect us since the dawn of time

Whether it’s a sad film, a joyous brought about – whether through
reunion or simply that you’ve just happiness, sadness or pain – the
banged your knee on a coffee table, brain’s cerebrum is aware that you
everyone has cried at some point in are undergoing a strong emotional
their life. But why have we evolved to do it? reaction to a stimulus. The
There’s a theory that it stems right back as far endocrine system releases a set of
as our pre-evolved days, where tears streaming hormones to the lacrimal gland,
down our primitive eyes and blurring our which secretes liquid onto the eye.
vision was a sign of surrender, proving that we Excess water can escapes down
meant our aggressor no harm. the nose, via the tear ducts.
But moving on to the present day, the science
shows that there are a number of sound Studies of tears have shown
biological reasons for tearing up. there is a biochemical reason
There are reflex tears, the stream caused by for emotional crying. While
getting smoke or sulphenic acid from a reflex tears are 98 per cent
chopped onion into your eye. When this water, emotional tears contain
happens, sensory nerves in your cornea send a several chemicals, including
signal to the brain that the eyes need adrenocorticotropic hormones
protecting. The brain then releases hormones present in times of stress, and leucine-
into the lacrimal glands located behind the enkephalin – an endorphin that releases pain
eyelid, which produces tears to provide a layer and improves your mood. Therefore, crying
of protection and to water down the irritant. appears to be a way of releasing
However, the more common form of crying is hormones and toxins that build
the emotional kind. When strong emotions are up during times of
intense emotion.

The lacrimal 1 Battle of
system the sexes
2
1 Lacrimal gland 3 While there is a stereotype that
women are tearier than men,
This gland receives the 4 there is some science to explain
message from the cerebrum the reasons behind this. Studies
to produce tears. have shown that women cry
about four times as often as
2 Cornea men and, while there are
cultural factors to be taken into
Tears help protect the surface consideration, there are
of the eye. biological factors too.

3 Tear ducts Until their adolescent years,
boys and girls cry fairly equally.
This is where the water flows As testosterone levels rise in
to. If there’s too much, it flows boys, they are more likely to get
down the face. angry than upset. Meanwhile,
girls gain increased oestrogen
4 Runny nose levels, which modifies
endorphin production, often
Tears that flow through the leading to more emotional
tear ducts go down a nasal responses to stimuli.
passage, which is what
causes a runny nose. 139

© SPL; Thinkstock

CURIOUS
QUESTIONS

168 148

What do Brain freeze
alveoli do? explained

155

Powering
cells

173

How do we
know how
much to
eat?

149 ©Thinkstock
©SPL
What makes
your nose run? ©Alamy

142 Ageing 153 Eyebrows / Earwax / Self 161 Correcting heart rhythms /
Why do we grow old? Do we need eyebrows? Salt / Adam’s apple
Is salt bad for your heart?
146 Left or right brained? 154 72-hour deodorant /
The truth behind thinking Modern fillings 162 Seasickness /
How do we combat body odour? Rumbling stomachs
148 Brain freeze Explaining seasickness
Why do we feel this cold pain? 155 What powers your cells?
Inside the mitochondria 163 What are moles?
149 Runny nose /Coma A look a mole formation
What makes your nose run? 156 Can we see thoughts?
Is this science or a myth? 164 Brain control / Laughing
150 Ears / Freckles / Do our brains control us?
Sore throat 158 How anaesthesia works
Why do your ears pop? The drug that stops pain signals 165 Dandruff / Eye adjustment /
Distance the eye can see
151 Memory / Toothpaste / 159 Stomach ulcers / Revealing how dandruff forms
Epidurals Mouth ulcers
What is a memory? How do ulcers form?

152 Blushing / Caffeine / Fainting 160 Hair growth / Blond hair
The telltale signs of blushing Our hair explained

140

156 170

Can we see What causes
thoughts? twins?

164

Do our
brains

098control us?

© SPL142
©SPL
© ThinkstockThe signs
of ageing

166 Allergies / Eczema 172 Paper cuts / Pins and 166
Why do some people suffer? needles / Funny bones
Why do paper cuts hurt so Allergies explained
167 Bruises / Water allergy / much?
Cholesterol |
How are bruises caused? 173 Aching muscles /
Fat hormone
168 How do alveoli help What causes muscle ache?
you breathe?
Inside your lungs 174 Raw meat / Inoculations /
Upper arm and leg
169 Migraines / Eye drops Should we eat raw meat?
Discover how migraines strike
175 Feet size / Gout
170 What are twins? How are feet measured?
What causes twins to be born?

141

CURIOUS QUESTIONS

Old age explained

© Science Photo Library

The ageing
process Whathappenstothe

human body as we age?

The whys of ageing, at its most basic our cells can no longer function. Free radicals – infirmities associated with ageing that have to do
level, seem simple: over the course of our unstable oxygen molecules that are a natural with stiffening or hardening of tissues, such as
lives, our bodies simply wear out. Or by-product of cell function – can build up and bond atherosclerosis.
that’s what we’ve been led to believe, to other cells. As a result, DNA can be damaged. They
anyway. Scientists who study gerontology, or the may also result in protein cross-linking, or Cells can also mutate on a genetic level due to
process of ageing, don’t yet have a definitive answer glycosylation, a phenomenon by which protein environmental or other factors. Problems with
as to why we age. There are two schools of thought. molecules in our bodies inappropriately bond mitochondria, structures that provide energy inside
The wear-and-tear concept – meaning our cells are together. They aren’t as elastic and don’t move or cells, can cause cells to die as well as diseases
used up over time – that many people subscribe to is break down like they’re supposed to. associated with old age such as Alzheimer’s disease.
just one example of an error theory.
Proponents of the error theory believe that There’s some evidence for this theory – wrinkles, Another group of theories puts forth the idea that
random external events cause damage that builds for example, are caused by a breakdown of collagen, our life spans are predetermined or programmed.
up in our bodies over the course of our lifetime until a type of protein found in the skin. Protein cross- One scenario suggests that the biological clock is
linking may also be responsible for a lot of ‘set’ by both our neuroendocrine system, which
produces hormones, and our immune system. The

142 | How It Works

F5ATCOTPS Grey hair Wrinkles Missing teeth Loss of eyesight Loss of hearing

SIGNS OF AGEING 1 When your hair turns grey has 2 The loss of skin elasticity also 3 Enamel on our teeth wears 4 With ageing can come a number 5 Age-related hearing loss can
a lot to do with your genetics, ages us through the creation of down over time and of vision problems that can be caused by everything from
but the loss of melanin wrinkles, although in some maintaining dental hygiene cause a loss of sight, including environmental factors to a
associated with grey hair is cases it can be prevented or at becomes more difficult, cataracts, glaucoma and degeneration of the fine hair
due to older age. least slowed down. resulting in tooth loss. macular degeneration. cells in the cochlea.

DID YOU KNOW? The process of ageing by a living system, or organism, is known as organismal senescence

Ageing skin Age spot Going grey Shaft

What looks like spots and Sun damage, as well as Each hair follicle in our heads The hair shaft itself is
wrinkles is actually a number of the ageing process in contains melanin – a pigment that composed of keratin, a
changes going on under the skin general, can cause gives our hair its colour. Over time the
clumps of melanin to melanin production decreases and fibrous protein.
Younger unpigmented hair begins to grow
Epidermis concentrate into spots.

The skin is kept smooth by Hair bulb
the proteins collagen and
elastin, which break down The bulb is at the base of
and lose their stretch over the root. It contains the
time, causing wrinkles. follicle, which forms a
socket for the hair.
Hair root

The root comprises three layers
– the outer root, the inner root
and the bulb – which gives hair
its structure and rigidity.

Papilla Cortex © Science Photo Library

This specialised cell is fed by Hair colour is
the bloodstream and is determined through
responsible for the growth the cortex, which is
of new hairs, and their
number of pigment cells. part of the shaft of
visible hair.

Subcutaneous fat layer Older Signs of Greying
ageing
As we age, the fat pads under the skin A reduction in
diminish and cause skin and muscle to sag. Hair loss melanin production
causes hair to grey.
A full head of hair
hypothalamus in the brain sends instead of 80 (the average life span in will thin as the Hearing loss © Gonzalo Haro
messages via hormones to the pituitary developed countries). Most researchers autoimmune system
gland, which in turn stimulates or believe that ageing is a complex process attacks the follicles. The sensory hair cells in the
restricts hormone secretions by the that no single theory can explain – it’s a cochlea deteriorate,
thyroid, adrenal glands, ovaries and combination of our genes, our biological Wrinkles causing age-related hearing
even the testicles. functions and environmental factors. loss, known as presbycusis.
These develop
Over time this complex system does We tend to focus more on the visible as collagen and 143
not function as efficiently, leading to signs of ageing at first, like wrinkles and skin cells begin
everything from problems sleeping to grey hairs, and these changes are prime to deteriorate.
menopause (which is a normal part of examples of how complicated the
ageing for women, but can lead to process can be. We’ve already talked a Skin tone
additional health problems). bit about the cause of wrinkles: the
connective tissues collagen and elastin, Decreased
Different types of cells in the that keep skin looking smooth, both subcutaneous fat
immune system decline in number as break down over time. Without the firm and elastic tissues
we age and do not function as well. Some connections underneath, the skin sags. cause sagging.
scientists point to the fact that the overall Many people lose fat deposits in their
risk of contracting cancers goes up as we faces, and the skin’s oil production
get older; younger, more efficient decreases. Many of these things have a
immune systems may have been able to genetic component, but outside factors
fend them off. such as exposure to ultraviolet radiation
and smoking both cause wrinkles and
Or it could all simply be genetic. That sags faster. The Sun’s rays break down
is, our DNA tells our bodies when life is at connective tissues, while smoking
an end. There does seem to be a genetic causes blood vessels to contract.
component to ageing among most
animals – they have predictable life Grey hair is caused by a loss of
spans. Women also tend to live longer melanin, the pigment that is responsible
than men. If your parents lived a long for our hair colour. Only recently have
time, you are more likely to do so scientists learned that melanin
yourself. One group of genes, known as production gets interrupted when
the longevity assurance gene, ha been hydrogen peroxide levels in the body
determined to influence life span. If you increase over time. Other proteins found
inherit the ‘helpful’ version then you are in hair cells that are responsible for
more likely to have a longer life. regrowth diminish over time too. Unlike
with wrinkles, however, there isn’t much
Although our genes play a part in our you can do to avoid going grey other than
life span, obviously they can be dye your hair. Genetics do appear to play
influenced or changed. Otherwise, we’d
still be living to the ripe old age of 30

CURIOUS QUESTIONS

Old age explained

a part, though. If your parents went corresponding decrease in growth Bone loss
grey at a young age, it is likely that you factors (hormones or proteins that
will too. stimulate cell growth). Loss of tone in A condition that affects ageing bones
muscles such as the anal sphincter
The internal signs of ageing are and the bladder can cause one of the Osteoporosis is a degenerative bone disease that results in lower bone density,
more serious, health-wise, than the most embarrassing signs of ageing for which makes the bones weak and fragile. The risk of falling as well as breaking
external ones. When and how they many people: incontinence. bones increases as the disease worsens. It is caused by a loss of the minerals that
occur are also based on a wide make up bone, such as calcium. There is a genetic factor, and the decrease of sex
variety of factors. Some gerontologists The ageing brain is still very hormones in both genders increase the likelihood of developing osteoporosis.
like to generalise that some parts of mysterious compared with what we
the body get harder as we age, while know about the rest of the human © SPL
others get softer, but everything is body. It was once thought that
interconnected. As we mentioned age-related issues such as memory 1. Healthy bone 2. Bone with osteoporosis
before, arteries get harder due to a loss had to do with a decrease in
buildup of plaque. The heart builds neurons. Now, however, researchers Healthy bones contain tight, Bones with osteoporosis have
up pressure because it has to work believe that unless you have a specific strong structures and are able to gapped, porous structures. They
more to pump blood through the disease that damages neurons, are fragile and can fracture easily,
harder, narrower blood vessels, complex chemical processes are easily bear body weight in
which results in high blood pressure. more likely to blame. For example, most circumstances. as well as lead to falls.
Other muscles, like the lungs, get the brains of people with Alzheimer’s
harder due to calcium deposits. disease tend to have deposits of
These can be caused by hormonal fibrous proteins called amyloids. The
changes or from having serious exact cause remains unknown,
infections such as tuberculosis. although one current theory is that
the amyloids manage to get into the
Meanwhile, hormonal changes brain because the system that
cause calcium to leech from the regulates the exchange of blood in
bones, making them soft and brittle the brain, known as the blood-brain
and reducing their density. Known as barrier, malfunctions.
osteoporosis, this loss means that
we’re at a greater risk of breaking What is arguably most fascinating
bones. Sarcopenia, or loss of muscle about the ageing process is that it’s
mass, is another ‘soft’ sign of ageing. different for everyone and it’s
Muscles contain special cells called unpredictable in so many ways.
satellites, a form of stem cell. These Thanks to the advances being made
cells are responsible for muscle in medicine, we’re learning more
growth as well as regeneration when every day about not only what causes
there’s some form of damage. These the most unpleasant signs of ageing,
cells gradually become less proficient but also what we can possibly do to
over time, possibly due to a counteract them.

The seven 3. Puberty 5. Adulthood 6. Late adulthood
stages of man
This growth spurt Muscles are After middle age tissues
What are the principal indicates the start developed and begin to deteriorate and
stages of the visible of sexual maturity. strong. Organs are weaken, while hair loses
human ageing process Girls tend to reach fully functional. its pigmentation.
throughout our lives? puberty two years
earlier than boys.

1. Infancy

The completely
dependent infant
experiences rapid
physical growth.

2. Childhood 4. Young adulthood

Tissue, muscle and A period of increasing
bone then grow physical maturity and body
gradually until puberty. development.

144 | How It Works

HEAD DRASTIC 1. Nutritional MORE DRASTIC 2. Hormone MOST DRASTIC 3. Plastic
changes therapy surgery
2HEAD
WAYS TO Antioxidants such as vitamin E The use of hormones such The visible signs of ageing
BEAT AGEING and calorie-restrictive diets as human growth hormone can be combated –
have both been shown to to combat signs of ageing, temporarily – through
extend life span, but not such as decreased muscle surgery and other
without potential health risks. mass, is very controversial. cosmetic procedures.

DID YOU KNOW? Ageing changes can be universal (happen to most people) or probabilistic (only occur in some people)

5 Life expectancy
21 around the world

80+ 4 6 1. Europe 5. Asia
77.5-80
75-77.5 3 7 Much of Europe enjoys a Asia has nearly every range of life
72.5-75 8 healthy life expectancy of more expectancy within its borders.
70-72.5 than 72 years.
67.5-70 6. Japan
65-67.5 2. North America
60-65 Japan is the Asian country with
55-60 Canadians have a slightly higher the highest average life
50-55 life expectancy than Americans. expectancy on the continent.
45-50
40-45 3. South America 7. Indonesia
0-40
The largest country has one of Indonesia is roughly on a par
the lowest life expectancies. with much of Asia.

4. Africa 8. Australia and
New Zealand
Most of Africa, being
undeveloped, has much lower These industrialised countries
life expectancy. have an 80+ life expectancy.

The senses Cataracts © Science Photo Library

All of the senses decline as we age. Hearing declines 1. Normal lens
because the structures in the ear break down over
time. Damage to the auditory nerve, which relays the In a person with a normal
signal to the brain, may also be to blame. Vision also lens, light from an image
lessens because older eyes are less responsive, passes through the lens and
sharp or sensitive. The eye muscles can also become is projected onto the tissue at
less responsive, resulting in a loss of peripheral the back of the eye called the
vision and a narrower depth of field. Taste and smell retina. The retina changes
both decrease with age as well. The 9,000 tastebuds the image to a nerve signal
with which we are born decrease over the course of and transmits it to the brain,
our lives. Smell may diminish due to a loss of nerve where it is processed.
endings in the nose. Decreased blood flow to the
areas of the brain and nervous system that receive 2. Lens with
touch information may be responsible for a loss of cataract
sensations like pain, cold, heat and vibration. The
brain itself gets smaller over time and chemical If protein clumps onto the
processes (as well as a lack of stimulation) result in lens (due to wear and tear or
age-related complaints such as memory loss. diseases like diabetes), it can
create a cloudy area known
as a cataract. Light is
diffused through the lens to
the retina, resulting in a
blurry image.

7. Old age Slowing down the
ageing process
A more elderly
appearance results Although ageing itself is inevitable (at least currently),
from wrinkles, hair there’s a lot that we can do to slow down the ageing
loss and decreased process. Visible signs of ageing like wrinkles can be
muscle tone. diminished by avoiding Sun exposure and other risk
factors like smoking. Internal signs of ageing can all be
© Science Photo Library combated to some extent by lifestyle changes. Weight- There are a number of ways to
bearing exercises such as weight-lifting, for example, slow down the ageing process
have been shown to help maintain bone density and © SPL
stave off osteoporosis. Aerobic exercise like walking or 145
cycling can prevent weight gain – which leads to
numerous diseases and conditions that age us – as well
as improve cardiovascular health. Diet also plays a part
in ageing – a balanced one can not only reduce the risk of
diseases like type two diabetes but also keep our
immune systems operating at their peak for longer.
Some researchers treat ageing like a disease. To that
end, stem-cell treatments and even cryogenics are
looked to as a potential cure. But at what cost? Others
feel that we weren’t meant to live forever and should
focus on ways to age comfortably.

CURIOUS QUESTIONS

How we think

Left or right brained?

Actually, you’re neither. Discover the truth behind the way we think

It’s true that the different sides of of over 1,000 people, in order to determine local hubs, each responsible for a different
the brain perform different tasks, whether the networks on one side of the brain set of functions.
but do these anatomical were stronger than the networks on the other.
asymmetries really define our Hubs with related functions cluster
personalities? Some psychologists argue that Despite the popularity of the left versus right together, preferentially developing on the
creative, artistic individuals have a more brain myth, the team found no difference in the same side of the brain, and allowing the nerves
developed right hemisphere, while analytical, strength of the networks in each hemisphere, to communicate rapidly on a local scale. One
logical people rely more heavily on the left side or in the amount we use either side of our example is language processing – in most
of the brain, but so far, the evidence for this brains. Instead, they showed that the brain is people, the regions of the brain involved in
two-sided split has been lacking. more like a network of computers. Local nerves speech, communication and verbal reasoning
In a study published in the journal PLOS ONE, can communicate more efficiently than distant are all located on the left-hand side.
a team at the University of Utah attempted to ones, so instead of sending every signal across
answer the question. They divided the brain up from one hemisphere of the brain to the other, Some areas of the brain are less symmetrical
into 7,000 regions and analysed the fMRI scans neurones that need to be in constant than others, but both hemispheres are used
communication tend to develop into organised relatively equally. There is nothing to say you
can’t be a brilliant scientist and a great artist.
Examining the human brain Parietal lobe
(pressure, taste) Occipital lobe
What do the different parts of the brain actually do? (vision)
The parietal lobes handle
Broca’s area Incoming information
(speech) sensory information and from the eyes is
processed at the
Broca’s area is responsible are involved in spatial back of the brain in
for the ability to speak and the visual cortex.
is almost always found on awareness and navigation.
the left side of the brain.

Frontal lobe
(planning,
problem solving)

At the front of each

hemisphere is a frontal

lobe, the left side is more

heavily involved in speech

and verbal reasoning,

while the right side

handles attention.

Auditory cortex Temporal lobe
(hearing) (hearing, facial
recognition, memory)
The auditory cortex is
The temporal lobes are
responsible for processing
involved in language
information from the ears
processing and visual memory.
and can be found on both

sides of the brain, in the

temporal lobes.

Wernicke’s area
(speech
processing)

The region of the brain

responsible for speech

processing is found on

the left-hand side.

146

billion

NEURONS
SYNAPSES

MASS
THE >100 1.4kg100 metres POWER
NERVE IMPULSE SPEED CONSUMPTION
86STATS
trillion 20W20%per second
BRAINY NUMBERS OXYGEN
USAGE

DID YOU KNOW? It is a myth that we only use ten per cent of our brains; even at rest, almost all brain regions are active

Give your brain a
fun workout

1Boost your memory
Look at this list of items for one minute,
then cover the page and see how many you
can remember:

9e_d Telephone Grape
Duck
Key FejWje F_bbemYWi[
F[dY_b
It took 82,944 Teacup Bicycle
computer processors
40 minutes to simulate A microscopic image of Match Table
just one second of the brain’s extremely
human brain activity, complex neural network
it’s that powerful

Myth-taken identity Difficult? Try again, but this time, make up a
story in your head, linking the objects
The left vs right brain personality myth is actually left, they couldn’t describe it. Speech and language together in a narrative.
based on Nobel Prize-winning science. In the are processed on the left side of the brain, but the
1940s, a radical treatment for epilepsy was trialled; information from the left eye is processed on the “Dofutprooceknfintendddohhoiirss utphtteeeuavrrecenurewypdwes,rheere”
doctors severed the corpus callosum of a small right. The patients were unable to say what they table
number of patients, effectively splitting their brains saw, but they could draw it. Psychologists
in two. If a patient was shown an object in their wondered whether the differences between the
right field of view, they had no difficulty naming it, two hemispheres could create two distinctive
but if they were shown the same object from the personality types, left-brained and right-brained.

TO DO:

Left BANG Right

Planner Impulsive …You get the idea. Make it as silly as you like;
strange things are much more memorable
?!@# than the mundane.

Rational Emotional 2Slow brain ageing
Learning a new language is one of the
Problem solving Creative best ways to keep your brain active. Here are © Corbis; Thinkstock
four new ways to say hello:
Precise Intuitive
š Feb_i^0 9p[i´Y´
(che-sh-ch)

š Hkii_Wd0 PZhWlijlk`
pZhW^#ijleeo
š 7 hWX_Y0 CWh^WXW

(mar-ha-ba)
š I mW^_b_0 >k`WcXe

(hud-yambo)

Logical Spiritual

Dog lovers Cat lovers

147

CURIOUS QUESTIONS

Brain freeze

The Ophthalmic branch What is ‘brain
carries sensory messages freeze’?
from the eyeball, tear gland,
upper nose, upper eyelid, That intense pain you sometimes get when
forehead, and scalp. you eat ice cream too fast is technically
called sphenopalatine ganglioneuralgia,
and it’s related to migraine headaches

The pain of a brain freeze, also know as an ice cream headache, comes from
your body’s natural reaction to cold. When your body senses cold, it wants
to conserve heat. One of the steps it takes to accomplish this is constricting
the blood vessels near your skin. With less blood flowing near your skin,
less heat is carried away from your core, keeping you nice and warm.
The same thing happens when something really cold hits the back of your mouth.
The blood vessels in your palate constrict rapidly. When the cold goes away (because
you swallowed the ice cream or cold beverage), they rapidly dilate back to their
standard, normal state.
This is harmless, but a major facial nerve called the trigeminal lies close to your
palate and this nerve interprets the constriction/dilation process as pain. The location
of the trigeminal nerve can cause the pain to seem like its coming from your forehead.
Doctors believe this same misinterpretation of blood vessel constriction/dilation is the
cause of the intense pain of a migraine headache.

“A major
facial nerve

called the
trigeminal
lies close to
your palate”

The Mandibular branch
carries sensory signals
from the skin, teeth and
gums of the lower jaw, as
well as tongue, chin, lower
lip and skin of the
temporal region.

The trigeminal facial nerve The Maxillary branch carries
is positioned very close to sensory messages from the
the palate. This nerve skin, gums and teeth of the
interprets palate blood upper jaw, cheek, upper lip,
vessel constriction and lower nose and lower eyelid.
dilation as pain.

148

What makes your nose run?

Discover what is going on inside a blocked nose and why it gets runny when we’re ill

It surprises many people but the main Cilia Mucus Goblet cell Epithelial cells
culprit responsible for a blocked and
runny nose is typically not excess Tiny hair-like The glycoproteins that The lining of the nose The nose is lined
mucus but swelling and inflammation. structures move make up mucus dissolve in has many mucus- by epithelial cells,
If the nose becomes infected, or an allergic mucus towards the water, forming a gel-like producing goblet cells.
reaction is triggered, the immune system produces back of the throat so substance that traps debris. covered in cilia.
large quantities of chemical messengers that cause that it can be The more water, the runnier
the local blood vessels in the lining of the nose to swallowed. the mucus.
dilate. This enables more white blood cells to enter
the area, helping to combat the infection, but it also
causes the blood vessels to become leaky, allowing
fluid to build up in the tissues.
Decongestant medicine contains a chemical that’s
similar to adrenaline, which causes the blood
vessels to constrict, stopping them from leaking.

Connective
tissue

Beneath the cells

lining the nose is a

layer of connective

tissue that is rich

in blood vessels.

Macrophage Blood vessels

Cells of the immune Inflammatory chemical signals
system produce chemical cause blood vessels to dilate,
mediators like histamine, allowing water to seep into the
which cause local blood tissues, diluting the mucus and
vessels to become leaky. making it runny.

How do we bring a
person out of a coma?

When we talk about ‘bringing Doctors induce the coma
someone out of a coma’, we are using a controlled dose of
referencing medically induced drugs. To bring the person out
comas. A patient with a of the coma, they simply stop
traumatic brain injury is the treatment. Bringing the
deliberately put into a deep patient out of the coma doesn’t
state of unconsciousness in wake them immediately. They
order to reduce swelling and gradually regain consciousness
allow the brain to rest. When over days, weeks or longer.
the brain is injured, Some people make a full
it becomes inflamed. The recovery, others need
swelling damages the brain rehabilitation or lifetime care
because it is squashed inside and others may remain
the skull. unaware of their surroundings.

149

© Thinkstock CURIOUS QUESTIONS

Ears popping / Sore throats / Freckles

Why do our ears
‘pop’ on planes?

The eardrum is a thin membrane that helps to transmit sound. Air
pressure is exerted on both sides of the eardrum; with the
surrounding atmospheric pressure pushing it inwards while air
being delivered via a tube between the back of your nose and the
eardrum pushes it outwards. This tube is called the Eustachian tube, when
you swallow ot opens and a small bubble of air is able to move causing a ‘pop’.
Rapid altitude changes in planes make the ‘pop’ much more noticeable
due to bigger differences in pressure. Air pressure decreases as a plane
ascends; hence air must exit the Eustachian tubes to equalise these pressures,
again causing a ‘pop’. Conversely, as a plane descends, the air pressure starts
to increase; therefore the Eustachian tubes must open to allow through more
air in order to equalise the pressure again, causing another ‘pop’.

What are freckles?

Freckles are clusters of the pigment melanin. It is
produced by melanocytes deep in the skin, with greater
concentrations giving rise to darker skin tones, and
hence, ethnicity. Melanin protects the skin against
harmful ultraviolet sunlight, but is also found in other locations
around the body,. Freckles are mostly genetically inherited, but not
always. They become more prominent during sunlight exposure,
as the melanocytes are triggered to increase production of melanin,
leading to a darker complexion. People with freckles generally have
pale skin tones, and if they stay in the Sun for too long they can
damage their skin cells, leading to skin cancers like melanoma.

“Rapid altitude
changes make
the ‘pop’ much
more noticeable”

Why does hot honey

and lemon help your
throat when it’s sore?

Honey and lemon can be areas. This means it will be less © Thinkstock
drank warm as a comfort painful when these areas come into
remedy when suffering contact with other surfaces when you
from a sore throat or cold, eat or swallow.
and is a popular drink with many
who are feeling unwell. The idea is Lemon also helps to settle the
that honey coats the throat and stomach too, as it contains acid,
therefore any inflamed areas will be which can be particularly helpful
‘protected’ by a layer of honey, while when experiencing an upset stomach
at the same time soothing painful from the effects of a cold or other
digestion-related illness.

150