Illustrated Medical Dictionary; Essential A-Z Quick Reference to over 5,500 Medical Terms - Dorling Kindersley DK Publishing ( PDFDrive )

WHIPPLE’S DISEASE WHITLOW

WHIPLASH INJURY

Cervical Cervical
vertebra joint

Ligaments Ligaments

BACKWARD FORCE (HYPEREXTENSION) FORWARD FORCE (FLEXION)

(see spinal injury). Characteristically, pain Diagnosis is through the identification

and stiffness in the neck are much worse of whipworm eggs in the faeces. Treat-

24 hours after the injury. ment is with anthelmintic drugs, such as

Treatment may include immobiliza- mebendazole. A heavy infestation may re-

tion in an orthopaedic collar, analgesic quire more than 1 course of treatment.

drugs, muscle-relaxant drugs, and phys- whitehead A very common type of skin

iotherapy. It may take a few weeks before blemish (see milia).

full pain-free movement is possible. white matter Tissue in the nervous sys-

Whipple’s disease A rare disorder, also tem composed of nerve fibres (axons).

called intestinal lipodystrophy, that can White matter makes up the bulk of the

affect many organs. Symptoms include cerebrum (the 2 large hemispheres of

steatorrhoea as a result of malabsorption, the brain) and continues down into the

abdominal pain, joint pains, progressive spinal cord; its main role is to transmit

weight loss, swollen lymph nodes, anae- nerve impulses. (See also grey matter.)

mia, and fever. The heart, lungs, and WHITE MATTER
brain can also be affected. The condition

is most common in middle-aged men. White matter
The cause is thought to be bacterial;

affected tissues are found to contain
macrophages (a type of scavenging cell) Cerebrum

containing rod-shaped bacteria. Treat-

ment is with antibiotic drugs for at least Grey
1 year. Dietary supplements are used to matter

correct nutritional deficiencies occur-

ring as a result of malabsorption. Brain stem

Whipple’s operation A type of panc-

reatectomy in which the head of the Cerebellum
pancreas and the loop of the duodenum

are surgically removed. Spinal cord

whipworm infestation Small, cylindrical
W whip-like worms, 2.5–5 cm long, that live
SECTION THROUGH BRAIN

in the human large intestine. Infestation

occurs worldwide but is most common whitlow An abscess on the fingertip or

in the tropics. Light infestation causes no toe, causing the finger to swell and be-

symptoms; heavy infestation can cause come extremely painful and sensitive to

abdominal pain, diarrhoea, and, some- pressure and touch. It most commonly

times, anaemia, since a small amount of develops from acute paronychia. A whit-

the host’s blood is consumed every day. low may be due to the virus that causes

598

WHO WITHDRAWAL SYNDROME

herpes simplex or to a bacterial infec- to emerge fully from the gum as a result W
tion. In some cases, it may be necessary of overcrowding (see impaction, dental).
to drain pus from the abscess. witches’ milk A thin, white discharge
WHO The commonly used abbreviation from the nipple of a newborn infant,
for the World Health Organization. caused by maternal hormones that
whooping cough See pertussis. entered the fetus’s circulation through
will, living See living will. the placenta. Witches’ milk occurs quite
Wilms’ tumour A type of kidney cancer, commonly. It is usually accompanied by
also called nephroblastoma, that occurs enlargement of 1 or both of the baby’s
mainly in children. breasts. The condition is harmless and
Wilson’s disease A rare, inherited dis- usually disappears spontaneously with-
order in which copper accumulates in in a few weeks.
the liver, resulting in conditions such as withdrawal The process of retreating
hepatitis and cirrhosis. Copper is slowly from society and from relationships
released into other body parts, damag- with others; usually indicated by aloof-
ing the brain, causing mild intellectual ness, lack of interest in social activities,
impairment, and leading to debilitating preoccupation with one’s own concerns,
rigidity, tremor, and dementia. Symp- and difficulty in communicating.
toms usually appear in adolescence but
can occur much earlier or later. Lifelong The term is also applied to the psy-
treatment with penicillamine is needed chological and physical symptoms that
and, if begun soon enough, can some- develop on discontinuing use of a sub-
times produce some improvement. If stance on which a person is dependent
the disease is discovered before the (see withdrawal syndrome).
onset of symptoms, the drug may pre- withdrawal bleeding Vaginal blood
vent them from developing. loss that occurs when the body’s level of
wind A common name for gas in the gas- oestrogen or progesterone hormones or
trointestinal tract, which may be expelled progestogen drugs drops suddenly.
through the mouth (see belching) or
passed through the anus (see flatus). The withdrawal bleeding that occurs at
the end of each month’s supply of com-
Babies often swallow air during feed- bined oral contraceptive pills mimics
ing which, unless the baby is “winded”, menstruation but is usually shorter and
can accumulate in the stomach and lighter. Discontinuation of an oestrogen-
cause discomfort. only or progestogen-only preparation
windpipe Another name for the trachea. also produces bleeding, which may dif-
wiring of the jaws Immobilization of fer from normal menstruation in its
the jaws by means of metal wires to amount and duration.
allow a fracture of the jaw to heal or as withdrawal method See coitus inter-
part of a treatment for obesity. ruptus.
withdrawal syndrome Unpleasant men-
When a fracture is being treated, the tal and physical symptoms experienced
jaws are kept wired in a fixed position for when a person stops using a drug on
about 6 weeks. For promoting weight which he or she is dependent (see drug
loss, the jaws are wired for as long as a dependence). Withdrawal syndrome most
year. In both cases, the person is unable commonly occurs in those with alcohol
to chew and can take only a liquid or dependence or dependence on opioids,
semi-liquid diet. This form of diet treat- in smokers, and in people addicted to
ment often fails because the person tranquillizers, amfetamines, cocaine, mari-
resumes previous eating habits follow- juana, and caffeine.
ing removal of the wires.
wisdom tooth One of the 4 rearmost Alcohol withdrawal symptoms start 6–8
teeth, also known as 3rd molars. The hours after cessation of intake and may
wisdom teeth normally erupt between last up to 7 days. They include trembling
the ages of 17 and 21, but in some peo- of the hands, nausea, vomiting, sweat-
ple, 1 or more fails to develop or erupt. ing, cramps, anxiety, and, sometimes,
In many cases, wisdom teeth are unable seizures. (See also confusion, delirium
tremens, and hallucinations.)

599

WOBBLE BOARD WOUND

Opioid withdrawal symptoms start after notably smallpox, tuberculosis, and mal-

8–12 hours and may last for 7–10 days. aria. Other functions include sponsoring

Symptoms include restlessness, sweat- medical research programmes, organiz-

ing, runny eyes and nose, yawning, ing a network of collaborating national

diarrhoea, vomiting, abdominal cramps, laboratories, and providing expert advice

dilated pupils, loss of appetite, irritabil- and specific targets to its 160 member

ity, weakness, tremor, and depression. states with regard to health matters.

Withdrawal symptoms from barbiturate worm infestation Several types of worm,

drugs and meprobamate start after 12–24 or their larvae, existing as parasites of

hours, beginning with tremor, anxiety, humans. They may live in the intestines,

restlessness, and weakness, sometimes blood, lymphatic system, bile ducts, or

followed by delirium, hallucinations, and, in organs such as the liver. In many

occasionally, seizures. A period of pro- cases, they cause few or no symptoms,

longed sleep occurs 3–8 days after onset. but some can cause chronic illness.

Withdrawal from benzodiazepine drugs There are 2 main classes: roundworms

may begin much more slowly and can and platyhelminths, which are subdiv-

be life-threatening. ided into cestodes (tapeworms) and

Withdrawal symptoms from nicotine trematodes (flukes).

develop gradually over 24–48 hours and Worm diseases found in developed

include irritability, concentration prob- countries include threadworm infestation,

lems, frustration, headaches, and anxiety. ascariasis, whipworm infestation, toxocar-

Discontinuation of cocaine or amfe- iasis, liver-fluke infestation, and various

tamines results in extreme tiredness, tapeworm infestations. Those occurring

lethargy, and dizziness. Cocaine with- in tropical regions include hookworm

drawal may also lead to tremor, severe infestation, filariasis, guinea worm dis-

depression, and sweating. ease, and schistosomiasis.

Withdrawal symptoms from marijuana

include tremor, nausea, vomiting, diar- WORM INFESTATION

rhoea, sweating, irritability, and sleep Threadworm egg Larva inside egg
problems. Caffeine withdrawal may lead

to tiredness, headaches, and irritability.

Severe withdrawal syndromes require

medical treatment. Symptoms may be

suppressed by giving the patient small

quantities of the drug he or she had been

taking. More commonly, a substitute drug

is given, such as methadone for opioid

drugs or diazepam for alcohol. The dose

of the drug is then gradually reduced.

wobble board A balancing board used MICROSCOPIC VIEW OF WORM EGGS
during physiotherapy to improve mus-

cle strength and coordination in the

feet, ankles, and legs. A wobble board is Worms may be acquired by eating

sometimes used after an ankle sprain. undercooked, infected meat, by contact

womb See uterus. with soil or water containing worm lar-

word blindness See alexia; dyslexia. vae, or by accidental ingestion of worm

World Health Organization (WHO) eggs from soil contaminated by infected
faeces. Most infestations can be easily
W An international organization estab- eradicated with anthelmintic drugs.
lished in 1948 as an agency of the

United Nations with responsibilities for wound Any damage to the skin and/or

international health matters and public underlying tissues caused by an accident,

health. The WHO headquarters are in act of violence, or surgery. Wounds in

Geneva, Switzerland. which the skin or mucous membrane is

The WHO has campaigned effectively broken are called open; those in which

against some infectious diseases, most they remain intact are termed closed.

600

WOUND INFECTION WRY NECK

Wounds can be divided into the follow- Triquetrum WRIST
ing categories: an incised wound; an Ulna
abrasion (or graze); a laceration; a pene- Pisiform Radius
trating wound; and a contusion. Hamate Lunate
wound infection Any type of wound is Capitate Scaphoid
susceptible to the entry of bacteria; the Trapezium
resultant infection can delay healing,
result in disability, and may even cause Trapezoid
death. Infection of a wound is indicated
by redness, swelling, warmth, pain, and BONES OF WRIST W
sometimes by the presence of pus or
the formation of an abscess. Infection displaced backwards. In young children,
may spread locally to adjacent organs similar displacement results from a frac-
or tissue, or to more distant parts of the ture through the epiphysis (growing end)
body via the blood. of the radius. A sprain can affect liga-
ments at the wrist joint, but most wrist
The type of infection depends upon sprains are not severe. (See also carpal
how the wound occurred. For example, tunnel syndrome; wrist-drop; tenosyn-
wounds brought into contact with soil ovitis; and osteoarthritis.)
can result in tetanus. STAPHYLOCOCCI, wrist-drop Inability to straighten the
including MRSA, are also common wrist, so that the back of the hand can-
wound infections. not be brought into line with the back
of the forearm. This causes weakness of
Once infection is discovered, a sample grip because the hand muscles can func-
of blood or pus is taken and the patient tion efficiently only when the wrist is
is given an antibiotic drug. Any abscess held straight.
should be drained surgically.
wrinkle A furrow in the skin. Wrinkling is Wrist-drop is caused by damage to the
a natural feature of aging and is caused radial nerve, either by prolonged pres-
by a loss of skin elasticity. Premature sure in the armpit (see crutch palsy) or
deep wrinkling is usually due to overex- by fracture of the humerus (see humerus,
posure to the ultraviolet rays in sunlight, fracture of). Treatment involves holding
and to smoking. the wrist straight. This may be achieved
by means of a splint, but if damage to
No treatment can permanently restore the radial nerve is permanent, the usual
skin elasticity, although some vitamin A treatment is arthrodesis (surgical fusion)
derivatives are believed to reduce wrin- of the wrist bones in a straight position.
kling. A face-lift smoothes out wrinkles writer’s cramp See cramp, writer’s.
by stretching the skin, but the effects wry neck Abnormal tilting and twisting of
last only about 5 years. the head. It may be due to injury to, or
wrist The joint between the hand and spasm of, the muscles on one side of the
the arm that allows the hand to be bent neck (see torticollis), among other factors.
forward and backward relative to the
arm and also to be moved side to side.

The wrist contains 8 bones (known
collectively as the carpus) arranged in 2
rows, one articulating with the bones of
the forearm, and the other connecting
to the bones of the palm. Tendons con-
nect the forearm muscles to the fingers
and thumb, and arteries and nerves sup-
ply the muscles, bones, and skin of the
hand and fingers.

Wrist injuries may lead to serious dis-
ability by limiting hand movement. A
common injury in adults is Colles’ frac-
ture, in which the lower end of the radius
is fractured and the wrist and hand are

601

XANTHELASMA X-RAYS

X Noncancerous skin tumours and skin
cancers also develop. Xeroderma pig-
mentosum is often accompanied by
related eye problems, such as photo-
phobia and conjunctivitis.

Treatment of the condition consists of

protecting the skin from sunlight. Skin

cancers are usually treated surgically or

with radiotherapy.

xanthelasma A yellowish deposit of xerophthalmia An eye disorder in which

fatty material that is visible in the skin vitamin A deficiency causes the conjunc-

around the eyes. Xanthelasmas are com- tiva and cornea to become abnormally

mon in elderly people and are usually dry. Without treatment, xerophthalmia

of no more than cosmetic importance. may progress to keratomalacia, a condi-

However, in younger people they may tion in which severe damage is caused

be associated with hyperlipidaemias, in to the cornea.

which there is excess fat in the blood. xerostomia Abnormal dryness of the

Xanthelasmas may be removed, if nec- mouth, which can cause bad breath and

essary, by a simple surgical procedure may predispose the sufferer towards

under a local anaesthetic. Any associated tooth decay (see caries, dental). Xerosto-

hyperlipidaemia must also be treated. mia is sometimes a symptom of Sjögren’s

(See also xanthomatosis.) syndrome. (See also mouth, dry.)

xanthoma A yellowish deposit of fatty xipamide A thiazide diuretic drug used

material in the skin, often on the elbow to treat oedema (accumulation of fluid

or buttock. They may be associated with in tissues) and high blood pressure.

hyperlipidaemias (see xanthomatosis). Side effects may include dizziness and

xanthomatosis A condition in which mild gastrointestinal disturbances.

deposits of yellowish, fatty material xiphisternum An alternative name for

develop in various parts of the body, the xiphoid process, the small, leaf-

particularly in the skin, internal organs, shaped projection that forms the lowest

corneas of the eyes, brain, and tendons. of the 3 parts of the sternum.

The deposits may occur only in the eye- X-linked disorders Sex-linked genetic

lids (see xanthelasma). A key feature of disorders in which the abnormal gene or

xanthomatosis is the tendency for fatty genes (the causative factors) are loca-

material to be deposited in the linings ted on the X chromosome. Almost all

of blood vessels, leading to generalized affected people are males. Haemophilia,

atherosclerosis. Xanthomatosis is often fragile X syndrome. and colour vision

associated with hyperlipidaemias. deficiency are examples.

Treatment aims to lower the levels of X-rays A form of electromagnetic radia-

fats in the blood by means of a diet that tion of short wavelength and high energy.

is low in cholesterol and high in poly- X-rays are widely used in medicine for

unsaturated fat, and by drug treatment. diagnosis and treatment because they

X chromosome A sex chromosome, of can be used to image bones, organs,

which every normal female body cell and internal tissues.

has a pair. Male body cells have 1 X and X-rays are produced artificially by

1 Y chromosome; each sperm carries bombarding a heavy metal tungsten tar-

either an X or a Y chromosome. Abnor- get with electrons, in a device known as

mal genes located on X chromosomes an X-ray tube. Low doses of the X-rays

cause X-linked disorders. that are emitted are passed through

X xeroderma pigmentosum A rare, in- body tissue and form images on film or
herited skin disease. The skin is normal a fluorescent screen. The X-ray image,

at birth, but photosensitivity (extreme also known as a radiograph or roent-

sensitivity to sunlight) causes it to genogram, shows the internal structure

become dry, wrinkled, freckled, and pre- of the area that is being examined.

maturely aged by about the age of 5. Dense structures, such as bone, absorb

602

X-RAYS, DENTAL XYLOMETAZOLINE

X-ray X-RAY
machine
Rib Spine Lung

Adjustable Beam of
stand X-rays

Heart Diaphragm

CHEST X-RAY IMAGE

X-ray film in
cassette

CHEST X-RAY PROCEDURE

X-rays well and appear white on an X- produce high-quality images with the X
ray image. Soft tissues, such as muscle, lowest possible radiation exposure to the
absorb less and appear grey. patient. The possibility of genetic dam-
age can be minimized by using a lead
Because X-rays can damage living shield to protect the patient’s reproduc-
cells, especially those that are dividing tive organs from X-rays. Radiographers
rapidly, high doses of radiation are used and radiologists wear a film badge to
for treating cancer (see radiotherapy). monitor their exposure to radiation.
(See also imaging techniques; radiogra-
Hollow or fluid-filled parts of the body phy; radiology.)
often do not show up well on X-ray film X-rays, dental See dental X-rays.
unless they first have a contrast med- xylitol A naturally occurring carbohydrate
ium (a substance that is opaque to that is only partially absorbed by the
X-rays) introduced into them. Contrast- body and is sometimes used as a sweet-
medium X-ray techniques are used to ener by people with diabetes. Xylitol
image the gallbladder (see cholecystogra- chewing gum has been shown to reduce
phy), bile ducts (see cholangiography), recurrent ear infections in some children.
the urinary tract (see urography), the Excess xylitol may lead to abdominal
gastrointestinal tract (see barium X-ray discomfort and flatulence.
examinations), blood vessels (see angiog- xylometazoline A decongestant drug
raphy; venography), and the spinal cord used in the form of a spray or drops to
(see myelography). relieve nasal congestion caused by a
common cold, sinusitis, or hay fever (see
X-rays can be used to obtain an image rhinitis, allergic). Xylometazoline is also
of a “slice” through an organ or part of used as an ingredient of eye-drops in the
the body by using a technique known as treatment of allergic conjunctivitis.
tomography. More detailed images of a
body slice are produced by combining Excessive use of xylometazoline may
tomography with the capabilities of a cause headache, palpitations, or drowsi-
computer (see CT scanning). ness. Long-term use of the drug may
cause nasal congestion to worsen when
Large doses of X-rays can be extremely treatment is stopped.
hazardous, and even small doses carry
some risk (see radiation hazards). Modern
X-ray film, equipment, and techniques

603

YAWNING YELLOW FEVER

Y and is absent in every female body cell.
Each sperm carries either a single X or a
single Y chromosome.

Unlike the X chromosome, the Y chro-
mosome carries little genetic material.
Its major function is to stimulate the

development of the testes in the embryo.

There are no significant diseases related

to abnormalities of the Y chromosome,

yawning An involuntary act, or reflex but hairy ears is a trait thought to be

action, usually associated with drowsi- determined by a Y-linked gene.

ness or boredom. The mouth is opened yeasts Types of fungi in which the body

wide and a slow, deep breath is taken of the fungus comprises individual cells

through it in order to draw air into the that occur either singly, in pairs, or in

lungs. The air is then slowly released. longer chains. Certain yeasts can cause

Yawning is accompanied by a momen- infections of the skin or mucous mem-

tary increase in the heart-rate, and, in branes; the most important of these

many cases, watering of the eyes. disease-causing yeasts is CANDIDA ALBI-

The purpose of yawning is unknown, CANS, which causes candidiasis.

but one theory suggests it is triggered YEASTS
by raised levels of carbon dioxide in the

blood; thus, its purpose could be to Nucleus
reduce the level of carbon dioxide and

increase that of oxygen in the blood.

yaws An infectious disease that tends Cytoplasm
to be found throughout poorer subtrop-

ical and tropical areas of the world.

Yaws is caused by a spirochaete (a spi- Cell wall
ral-shaped bacterium), and it spreads

principally in conditions of poor hygiene.

The infection is almost always acquired

in childhood, and it mainly affects the Mitochondrion

skin and bones.

The bacteria enter the body through YEAST CELL

abrasions in the skin. Three or 4 weeks

after infection, an itchy, raspberry-like yellow fever An infectious disease of

growth appears at the site of infection, short duration and variable severity that

sometimes preceded by fever and pains. is caused by a virus transmitted by mos-

Scratching spreads the infection and quitoes. In severe cases, the skin yellows

causes more growths to develop else- due to jaundice, from which the name

where on the skin. Without treatment, yellow fever derives. The infection may

the growths heal slowly over the course be spread from monkeys to humans in

of about 6 months, but recurrence is forest areas through various species of

common. In about 10 per cent of un- mosquito; and in urban areas it can be

treated cases, widespread tissue loss transmitted between humans by AEDES

eventually occurs. This may eventually AEGYPTI mosquitoes.

lead to gross destruction of the skin, Today, yellow fever is contracted only in

bones, and joints of the legs, nose, Central America, parts of South America,

palate and upper jaw. and a large area of Africa. Eradication of

Yaws can be cured by a single large the causative mosquito from populated

dose of a penicillin drug given as an areas has greatly reduced its incidence.

Y injection into muscle. Yellow fever is characterised by a sud-
Y chromosome A sex chromosome that den onset of fever and headache, often

is present in every normal male body with nausea and nosebleeds and, despite

cell. It is paired with an X chromosome the high fever, a very low heart-rate. In

604

YERSINIA YTTRIUM

more serious cases, the fever is higher yoga maintains flexibility of the body,
and there is severe headache and pain teaches both physical and mental con-
in the neck, back, and legs. Damage may trol, and is a useful relaxation technique.
occur rapidly to the liver and kidneys,
causing jaundice and kidney failure. This If attempted by people in poor health,
may be followed by severe agitation and or practised incorrectly, yoga may pose
delirium, leading to coma and death. certain health hazards, such as back
disorders, hypertension (high blood
Vaccination confers long-lasting immu- pressure), and glaucoma (increased pres-
nity and should always be obtained sure in the eye).
before travel to affected areas. A single yolk sac The membranous sac, other-
injection of the vaccine gives protection wise known as the vitelline sac, that lies
for at least 10 years. Reactions to the against, and is attached to, the front of
vaccine are rare and are usually trivial, the embryo during the early stages of its
although children under the age of 1 existence. During development, the sac
should not be vaccinated. decreases proportionately in size to the
body, reducing finally to a narrow duct
During yellow fever epidemics, diag- that passes through the umbilicus. The
nosis is simple. A diagnosis can be yolk sac is believed to assist in the trans-
confirmed by carrying out blood tests to portation of nutrients from the mother
isolate the causative virus or to find to the early embryo.
antibodies to the virus. yttrium A very rare metal that, in its
radioactive form, is sometimes used in
No drug is effective against the yellow cancer therapy and to treat joints affec-
fever virus; treatment is directed at ted by arthritis.
maintaining the blood volume. Transfu-
sion of fluids is often necessary. Many Y
patients recover in about 3 days and, in
mild to moderate cases, complications
are few. Relapses do not occur and one
attack confers lifelong immunity. Overall,
however, about 10 per cent of victims die.
yersinia A class of bacteria containing
the organism responsible for the bubonic
plague (YERSINIA PESTIS). In other forms,
yersinia is responsible for a variety of
infections, such as gastroenteritis, par-
ticularly in young children, and arthritis
and septicaemia in adults.
yin and yang The 2 opposing and
interdependent principles that are funda-
mental to traditional Chinese medicine
and philosophy. Yin is associated with
the female, darkness, coldness, and
quiescence; yang embodies qualities of
maleness, brightness, heat, and activity.
In a healthy body, yin and yang are in
balance. The concepts of yin and yang
are also central to the theoretical basis
of macrobiotics.
yoga A system of Hindu philosophy and
physical discipline that is becoming
increasingly popular throughout the
world. The main form of yoga that is
practised in the West is hatha-yoga, in
which the follower adopts a series of
poses, called asanas, and uses a special
breathing technique. The practice of

605

ZIDOVUDINE ZOONOSIS

Z Prolonged excessive intake of zinc may
interfere with the intestinal absorption
zidovudine An antiretroviral drug, for- of iron and copper, leading to a defi-
merly known as azidothymidine or AZT, ciency of these minerals.
that is used in combination with other
antiretroviral drugs to slow the progres- Zinc compounds, such as zinc oxide,
sion of AIDS. The principal aim of are included in many preparations for
antiretrovirals is to keep viral replica- treating skin and scalp disorders.
tion to as low a level as possible for as zinc oxide An ingredient of many skin
long as possible; they do not constitute preparations that has a mild astringent
a cure. Zidovudine was the first drug to action and a soothing effect. Zinc oxide
be introduced to combat HIV infection. is used to treat painful, itchy, or moist
Possible side effects of zidovudine skin conditions and to ease the pain
include anaemia, which may be severe caused by haemorrhoids and insect
enough to require a blood transfusion, bites or stings. It also blocks the ultra-
nausea, loss of appetite, and headache. violet rays of the sun (see sunscreens).
Zidovudine also impairs the absorption Zollinger–Ellison syndrome A rare
of trimethoprim and sulfamethoxazole, condition characterized by severe and
the antibiotic drugs used to treat pneu- recurrent peptic ulcers in the stomach,
monia in people who have AIDS, thus duodenum, and jejunum (the 2nd part
reducing the effectiveness of these drugs. of the small intestine). Zollinger–Elli-
son syndrome is caused by 1 or more
ZIFT See zygote intrafallopian transfer. tumours in the pancreas that secrete
zinc A trace element that is essential for the hormone gastrin. Gastrin stimulates
production of large quantities of acid by
normal growth, the development of the the stomach, which leads to ulceration.
reproductive organs, normal functioning The high levels of acid in the digestive
of the prostate gland, healing of wounds, tract often also cause diarrhoea.
and the manufacture of proteins and
nucleic acids in the body. Zinc also con- The tumours are cancerous, but of a
trols the activities of more than 100 slow-growing type. If possible, they are
enzymes and is involved in the func- removed surgically. Proton pump inhib-
tioning of the hormone insulin. itor drugs are given to treat the ulcers.
zolpidem A drug used in the short-term
Particularly rich sources of zinc include treatment of insomnia. Zolpidem has a
lean meat, wholemeal breads, whole brief duration of action and causes little
grain cereals, dried beans, and seafood. hangover effect. Side effects include diar-
rhoea, nausea, and dizziness.
Zinc deficiency is rare. Most cases occur zona pellucida The thick, transparent,
in people who are generally malnour- noncellular layer that surrounds a devel-
ished. Deficiency may also be caused by oping egg cell in the ovarian follicle. At
any disorder that causes malabsorption; fertilization, the zona pellucida is pene-
acrodermatitis enteropathica; or by in- trated by at least 1 sperm.
creased zinc requirements due to cell zoonosis Any infectious or parasitic
damage (for example, as a result of a disease of animals that can be transmit-
burn or in sickle cell anaemia). Symp- ted to humans. Unlike many disease
toms of deficiency include impairment organisms, zoonotic organisms are flex-
of taste and loss of appetite; there may ible and can adapt themselves to many
also be hair loss and inflammation of different species.
the skin, mouth, tongue, and eyelids. In
children, zinc deficiency impairs growth Zoonoses are usually caught from ani-
and delays sexual development. mals closely associated with humans,
either as pets, food sources, or scaven-
ging parasites, such as rats. Examples
include toxocariasis, cat-scratch fever,
some fungal infections, psittacosis, bru-
cellosis, trichinosis, and leptospirosis.
Rabies can infect virtually any mammal,

606

ZOPICLONE ZYGOTE INTRAFALLOPIAN TRANSFER

but dog bites are a common cause of ZYGOTE Zygote
human infection worldwide.
Zona pellucida
Other zoonoses are transmitted from
animals less obviously associated with The zygote travels down 1 of the
humans, usually by insect vectors. For woman’s fallopian tubes, dividing as it
example, yellow fever is transmitted by does so. After about a week, the mass of
mosquito bites. (See also dogs, diseases cells (now called a blastocyst) implants
from; cats, diseases from; rats, dis- into the lining of the uterus, and the next
eases from; insects and disease.) stage of embryological growth begins.
zopiclone A drug used in the short-term (See also embryo; fertilization.)
treatment of insomnia. It has a brief dura- zygote intrafallopian transfer A type
tion of action and causes little hangover of in vitro fertilization, also referred to as
effect. Side effects include a bitter metal- ZIFT, in which ova are fertilized outside
lic taste, nausea, and dry mouth. the body and returned to a fallopian
Z-plasty A technique that is used in tube rather than to the uterus.
plastic surgery to change the direction
of a pre-existing scar so that it can be
hidden in natural skin creases, or to
relieve skin tension caused by the con-
tracture of a scar. Z-plasty is especially
useful for revising unsightly scars on
the face and for releasing scarring across
those joints, such as on the fingers or in
the armpits, that may restrict normal
movement or cause deformity.
zygomatic arch The arch of bone,
commonly known as the cheek bone, on
either side of the skull just below the eye
socket. The zygomatic arch is formed of
the zygomatic and temporal bones.

ZYGOMATIC ARCH

Frontal Zygomatic Zygomatic arch
bone bone

Parietal bone

Temporal bone
Occipital bone

Mandible

zygote The cell that is produced when a
sperm fertilizes an ovum. A zygote, mea-
suring about 0.1 mm in diameter in
humans, contains all the genetic mat-
erial for a new individual. The zygote is
surrounded by a protein-rich layer
known as the zona pellucida.

607

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608

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