Main BMA Illustrated Medical Dictionary - Essential A-Z Quick Reference to over 5,500 Medical Terms

BMA Illustrated Medical Dictionary - Essential A-Z Quick Reference to over 5,500 Medical Terms

,
A colour-illustrated dictionary with easy-to-follow explanations for over 5,500 medical terms. Entries define the ailment, explain how it affects the patient, and outline possible treatments. Key conditions are accompanied by images to improve your understanding. From exploring a dental abscess diagram to discovering the symptoms and causes of asthma, stay one step ahead of your family's ailments following this A-Z guide.
Year: 2007
Edition: 1st
Language: english
Pages: 612
File: PDF, 38.02 MB
Download (pdf, 38.02 MB)
Preview

You may be interested in

 

Most frequently terms

 
 
davo
nice library i get best best book for me i don't have word b/c i live in remote area top happier to me thanks to Z-library
27 June 2019 (19:47) 
Emmazy
Plenty books to choose from
07 July 2019 (03:10) 
Jennie
Thumbs up! Thanks a lot.
07 July 2019 (11:12) 
Mehrdad
Fantastic book useful and easy
27 July 2019 (21:34) 
Drana
Best bookstore website ever and ever.Thank you very much for your full support on us as Medical professionals,every book i missed for long is here even more than I expected.
07 August 2019 (01:08) 
Jazz SHU
you are my live saver. thank for books, esp the medical book which I hardy to find in my country or it is too expensive for physical books. love you guys.
20 August 2019 (04:28) 
Nick
Best Book I've ever read.
27 August 2019 (08:24) 
Putra
Thank you, you guys are the best.
04 October 2019 (06:18) 
victor
Thumps up! Thanks for your sharing.
02 November 2019 (16:10) 
nadia
really gratefull for you
20 November 2019 (13:40) 
Jadoon
Thank you for sharing this
02 December 2019 (08:52) 
AL
thank you for everthing
12 December 2019 (15:04) 
You can write a book review and share your experiences. Other readers will always be interested in your opinion of the books you've read. Whether you've loved the book or not, if you give your honest and detailed thoughts then people will find new books that are right for them.
The British
Medical Association

ILLUSTRATED

MEDICAL
DICTIONARY
CORONARY ARTERY
Superior
vena cava

Pulmonary
veins

Right
main
coronary
artery

Aorta

Left main
coronary
artery
Left
circumflex
artery

Left
anterior
descending
artery
Coronary
vein

Inferior
vena cava

Descending
aorta

coronary Any structure that encircles like
a crown. The term usually refers to the
coronary arteries encircling the heart. It is
also sometimes used as a nonmedical
term for a heart attack (see myocardial
infarction).
coronary artery Either of the 2 main
arteries that supply the tissues of the
heart with oxygen-rich blood. These
arteries, known as the left and right main
coronary arteries, arise directly from the
aorta. The term coronary artery is also
applied to any of the arteries that branch
off from the main coronary arteries, such
as the left circumflex artery and the left
anterior descending artery. Blockage of a
coronary artery as a result of atherosclerosis can lead to myocardial infarction.
(See also coronary artery disease.)

Essential A–Z quick reference
to over 5,500 medical terms

The British
Medical Association

ILLUSTRATED

MEDICAL
DICTIONARY

A Dorling Kindersley Book

ABDOMEN

A

ABDOMINAL SWELLING

intake, eating unwisely, or an attack of
diarrhoea. Pain in the lower abdomen
is common during menstruation but is
occasionally due to a gynaecological
disorder such as endometriosis. Cystitis
is a common cause of pain or discomfort in the abdomen. Bladder distension
as a result of urinary obstruction may
also cause abdominal pain.
Abdominal colic is pain that occurs
every few minutes as one of the internal
organs goes into muscular spasm in an
attempt to overcome an obstruction
such as a stone or an area of inflammation. The attacks of colic may become
more severe and may be associated
with vomiting (see abdomen, acute).
Peptic ulcer often produces recurrent
gnawing pain. Other possible causes of
abdominal pain are infection, such as
pyelonephritis, and ischaemia (lack of
blood supply), as occurs when a volvulus (twisting of the intestine) obstructs
blood vessels. Tumours affecting an
abdominal organ can cause pain. Abdominal pain can also result from anxiety.
For mild pain, a wrapped hot-water
bottle is often effective. Pain due to
peptic ulcer can be temporarily relieved
by food or by taking antacid drugs.
Abdominal pain that is not relieved by
vomiting, persists for more than 6 hours,
or is associated with sweating or fainting requires urgent medical attention.
Urgent attention is also necessary if
pain is accompanied by persistent vomiting, vomiting of blood, or passing of
bloodstained or black faeces. Unexplained weight loss or changes in bowel
habits should always be investigated.
Investigation of abdominal pain may
include the use of imaging tests such as
ultrasound scanning, and endoscopic
examination in the form of gastroscopy,
colonoscopy, or laparoscopy.
abdominal swelling Enlargement of
the abdomen. Abdominal swelling is a
natural result of obesity and growth of
the uterus during pregnancy. Wind in the
stomach or intestine may cause uncomfortable, bloating distension of the
abdomen. Some women experience abdominal distension due to temporary
water retention just before menstruation. Other causes may be more serious.

A
abdomen The region of the body between the chest and the pelvis. The
abdominal cavity is bounded by the ribs
and diaphragm above, and by the pelvis
below, with the spine and abdominal
muscles forming the back, side, and
front walls. It contains the liver, stomach, intestines, spleen, pancreas, and
kidneys. In the lower abdomen, enclosed
by the pelvis, are the bladder, rectum,
and, in women, the uterus and ovaries.

ABDOMEN
Stomach
Liver

Large
intestine

Area of
abdomen

Small
intestine
Rectum

abdomen, acute Persistent, severe abdominal pain of sudden onset, usually
associated with spasm of the abdominal muscles, vomiting, and fever.
The most common cause of an acute
abdomen is peritonitis. Other causes
include appendicitis, abdominal injury,
perforation of an internal organ due to
disorders such as peptic ulcer or diverticular disease. Acute abdominal pain
commonly begins as a vague pain in the
centre but then becomes localized.
An acute abdomen requires urgent
medical investigation that may involve
a laparoscopy or a laparotomy. Treatment depends on the underlying cause.
abdominal pain Discomfort in the abdomen. Mild abdominal pain is common
and is often due to excessive alcohol
4

ABDOMINAL THRUST

ABSCESS

For instance, ascites (accumulation of
fluid between organs) may be a symptom of cancer or disease of the heart,
kidneys, or liver; swelling may also be
due to intestinal obstruction (see intestine, obstruction of) or an ovarian cyst.
Diagnosis of the underlying cause may
involve abdominal X-rays, ultrasound
scanning, laparotomy, or laparoscopy. In
ascites, some fluid between organs may
be drained for examination.
abdominal thrust A first-aid treatment
for choking, in which sharp upward pressure is applied to the upper abdomen
to dislodge a foreign body obstructing
the airway. The technique is also known
as the Heimlich manoeuvre.
abdominal X-ray An X-ray examination of the abdominal contents. X-rays
can show whether any organ is enlarged
and can detect swallowed foreign bodies in the digestive tract. They also show
patterns of fluid and gas: distended
loops of bowel containing fluid often
indicate an obstruction (see intestine,
obstruction of); gas outside the intestine
indicates intestinal perforation.
Calcium, which is opaque to X-rays, is
present in most kidney stones (see
calculus, urinary tract) and in some
gallstones and aortic aneurysms; these
can sometimes be detected on an
abdominal X-ray.
abducent nerve The 6th cranial nerve.
It supplies the lateral rectus muscle of
each eye, which is responsible for moving the eyeball outwards. The nerve
originates in the pons (part of the brainstem) and passes along the base of the
brain, entering the back of the eye socket
through a gap between the skull bones.
abduction Movement of a limb away
from the central line of the body, or of a
digit away from the axis of a limb. Muscles that carry out this movement are
called abductors. (See also adduction.)
ablation Removal or destruction of diseased tissue by excision (cutting away),
cryosurgery (freezing), radiotherapy, diathermy (burning), or laser treatment.
abnormality A physical deformity or
malformation, a behavioural or mental
problem, or a variation from normal in
the structure or function of a cell, tissue, or organ in the body.

ABO blood groups See blood groups.
abortifacient An agent that causes abortion. In medical practice, abortion is
induced using prostaglandin drugs,
often given as vaginal pessaries.
abortion In medical terminology, either
spontaneous abortion (see miscarriage)
or medically induced termination of
pregnancy (see abortion, induced).
abortion, induced Medically induced
termination of pregnancy. Abortion may
be performed if continuation of the
pregnancy would risk the woman’s life,
if the mental or physical health of the
woman or her existing children is at
risk, or if there is a substantial risk of
handicap to the baby.
Depending on the stage of pregnancy,
termination may be induced by using
drugs or by the surgical technique of
vacuum suction curettage, under either
a general or local anaesthetic, during
which the fetal and placental tissues are
removed. Complications are rare.
abrasion Also called a graze, a wound
on the skin surface that is caused by
scraping or rubbing.
abrasion, dental The wearing away of
tooth enamel, often accompanied by the
erosion of dentine (the layer beneath
the enamel) and cementum (the bonelike tissue that covers the tooth root),
usually through too-vigorous brushing.
Abraded areas are often sensitive to
cold or hot food or drink, and a desensitizing toothpaste and/or protection with
a bonding (see bonding, dental) agent or
filling may be needed.
abreaction In psychoanalysis, the process of becoming consciously aware of
repressed (buried) thoughts and feelings.
In Freudian theory, abreaction ideally
occurs by way of catharsis.
abscess A collection of pus formed as a
result of infection by microorganisms,
usually bacteria. Abscesses may develop
in any organ and in the soft tissues
beneath the skin in any area. Common
sites include the armpit, breast (see
breast abscess), groin, and gums (see
abscess, dental). Rarer sites include the
liver (see liver abscess) and the brain
(see brain abscess).
Common bacteria, such as staphylococci, are the usual cause of abscesses,
5

A

A

ABSCESS, DENTAL

ACANTHOSIS NIGRICANS

although fungal infections can cause
them, and amoebae are an important
cause of liver abscesses (see amoebiasis). Infectious organisms usually reach
internal organs via the bloodstream, or
they penetrate tissues under the skin
through a wound.
An abscess may cause pain, depending
on where it occurs. Most larger abscesses cause fever, sweating, and malaise.
Those that are close to the skin often
cause obvious redness and swelling.
Antibiotics, antifungal drugs, or amoebicides are usually prescribed as
appropriate. Most abscesses also need
to be drained (see drain, surgical), and
in some cases a tube may be left in
place to allow continuous drainage.
Some abscesses burst and drain spontaneously. Occasionally, an abscess
within a vital organ damages enough
surrounding tissue to cause permanent
loss of normal function, or even death.
abscess, dental A pus-filled sac in the
tissue around the root of a tooth. An
abscess may occur when bacteria
invade the pulp (the tissues in the central cavity of a tooth) as a result of
dental caries, which destroys the tooth’s
enamel and dentine, allowing bacteria
to reach the pulp. Bacteria can also gain
access to the pulp when a tooth is
injured. The infection in the pulp then
spreads into the surrounding tissue to
form an abscess. Abscesses can also
result from periodontal disease, in which
bacteria accumulate in pockets that
form between the teeth and gums.
The affected tooth aches or throbs,
and biting or chewing is usually
extremely painful. The gum around the
tooth is tender and may be red and
swollen. An untreated abscess eventually erodes a sinus (channel) through
the jawbone to the gum surface, where
it forms a swelling known as a gumboil.
As the abscess spreads, the glands in
the neck and the side of the face may
become swollen, and fever may develop.
Treatment may consist of draining the
abscess, followed by root-canal treatment of the affected tooth, but in some
cases extraction of the tooth is necessary. Antibiotics are prescribed if the
infection has spread beyond the tooth.

ABSCESS, DENTAL
Enamel

Dentine

Decay

Gum

Pulp
Blood
vessel
Nerve
Jawbone
Abscess

An abscess in a periodontal pocket can
usually be treated by the dentist scraping away infected material.
absence In medical terms, a temporary
loss or impairment of consciousness
that occurs in some forms of epilepsy,
typically generalized absence (petit
mal) seizures in childhood.
absorption The process by which fluids or other substances are taken up by
body tissues. The term is commonly
applied to the uptake of the nutrients
from food into blood and lymph from
the digestive tract. The major site of
absorption is the small intestine, which
is lined with microscopic finger-like
projections called villi (see villus). The
villi greatly increase the surface area of
the intestine, thereby increasing the
rate of absorption.
acanthosis nigricans A rare condition
in which thickened dark patches of skin
appear in the groin, armpits, neck, and
other skin folds. The condition may
occur in young people as a genetic disorder or as the result of an endocrine
disorder such as Cushing’s syndrome. It
also occurs in people with carcinomas
of the lung and other organs.
Pseudoacanthosis nigricans is a much
more common condition, usually seen
in dark-complexioned people who are
overweight. In this form, the skin in fold
areas is both thicker and darker than the
surrounding skin, and there is usually
excessive sweating in affected areas. The
condition may improve with weight loss.
6

ACARBOSE

ACETYLCHOLINESTERASE INHIBITORS

more difficult and results in a form of
longsightedness called presbyopia.
acebutolol A beta-blocker drug used to
treat hypertension, angina pectoris, and
certain types of arrhythmia in which the
heart beats too rapidly.
ACE inhibitor drugs A group of vasodilator drugs used to treat heart failure,
hypertension, and diabetic nephropathy.
ACE (angiotensin converting enzyme) inhibitors are often prescribed with other
drugs such as diuretic drugs or betablocker drugs. Possible side effects
include nausea, loss of taste, headache,
dizziness, and dry cough.
acetaminophen An analgesic drug
more commonly known as paracetamol.
acetazolamide A drug that is used in
the treatment of glaucoma and, occasionally, to prevent or treat symptoms
of mountain sickness. Possible adverse
effects include lethargy, nausea, diarrhoea, and impotence.
acetic acid The colourless, pungent, organic acid that gives vinegar its sour
taste. In medicine, acetic acid is an
ingredient of antiseptic gels that are
used for certain vaginal infections.
acetylcholine A type of neurotransmitter (a chemical that transmits messages
between nerve cells or between nerve
and muscle cells). Acetylcholine is the
neurotransmitter found at all nervemuscle junctions and at many other
sites in the nervous system. The actions
of acetylcholine are called cholinergic
actions, and these can be blocked by
anticholinergic drugs.
acetylcholinesterase inhibitors A
group of drugs that are used in the
treatment of mild to moderate dementia
due to Alzheimer’s disease, in which
there is a deficiency of the neurotransmitter acetylcholine in the brain.

acarbose A drug that is used to treat
type 2 diabetes mellitus. Acarbose acts
on enzymes in the intestines, inhibiting
the digestion of starch and therefore
slowing the rise in blood glucose levels
after a carbohydrate meal.
accessory nerve The 11th cranial nerve.
Unlike the other cranial nerves, most of
the accessory nerve originates from the
spinal cord. The small part of the nerve
that originates from the brain supplies
many muscles of the palate, pharynx
(throat), and larynx (voice box). Damage
to this part of the nerve may cause difficulty in speaking and swallowing. The
spinal part of the nerve supplies large
muscles of the neck and back, notably
the sternomastoid and trapezius. Damage to the spinal fibres of the nerve
paralyses these muscles.
accidental death Death that occurs as
a direct result of an accident. A high proportion of deaths in young adults,
particularly among males, are accidental. Many of these deaths are due to
road traffic accidents, drowning, or drug
overdose. Falls in the home and burning
or asphyxiation due to fire are common
causes of accidental death in elderly
people. Fatal accidents at work have
become less common with the introduction of effective safety measures.
accommodation Adjustment, especially
the process by which the eye adjusts
itself to focus on near objects. At rest,
the eye is focused for distant vision,
when its lens is thin and flat. To make
focusing on a nearer object possible,
the ciliary muscle of the eye contracts,
which reduces the pull on the outer rim
of the lens, allowing it to become thicker
and more convex.
With age, the lens loses its elasticity.
This makes accommodation more and

ACCOMMODATION
Light rays from
near object

Ciliary
muscle

Point of
focus

NEAR FOCUS

Light rays from
distant object

Rounded
lens bends
the light

Ciliary
muscle

7

Point of
focus

DISTANT FOCUS

Flattened
lens

A

A

ACETYLCYSTEINE

ACID–BASE BALANCE

Drugs such as donepezil and rivastigmine work by blocking the action of
acetylcholinesterase, the enzyme in the
brain responsible for the breakdown of
acetylcholine. This raises acetylcholine
levels, and, in half of all patients, the
drugs slow the rate of progression of
dementia. They have no effect on
dementia due to other causes, such as
stroke or head injury, however. Common side effects include nausea,
dizziness, and headache. Rarely, difficulty in passing urine may occur.
acetylcysteine A drug used in the treatment of paracetamol overdose and as a
mucolytic drug to loosen sputum. When
the drug is taken in large doses, vomiting
or rash may occur as rare side effects.
achalasia A rare condition of unknown
cause in which the muscles at the lower
end of the oesophagus and the sphincter (valve) between the oesophagus and
the stomach fail to relax to let food into
the stomach after swallowing. As a
result, the lowest part of the oesophagus is narrowed and becomes blocked
with food, while the part above widens.
Symptoms include difficulty and pain
with swallowing and pain in the lower
chest and upper abdomen.
A barium swallow (a type of barium
X-ray examination) and gastroscopy may
be performed to investigate achalasia.

ACHILLES TENDON

Violent stretching of the tendon can
cause it to rupture; in such cases, surgical repair may be necessary.
achlorhydria Absence of stomach acid
secretions. This may be due to chronic
atrophic gastritis or to an absence or
malfunction of acid-producing parietal
cells in the stomach lining. Achlorhydria
may not produce symptoms but is associated with stomach cancer, however,
and is a feature of pernicious anaemia
(see anaemia, megaloblastic).
achondroplasia A rare genetic disorder of bone growth that leads to short
stature. The condition is caused by a
dominant gene (see genetic disorders)
but often arises as a new mutation. The
long bones of the arms and legs are
affected mainly. The cartilage that links
each bone to its epiphysis (the growing
area at its tip) is converted to bone too
early, preventing further limb growth.
Those affected have short limbs, a welldeveloped trunk, and a head of normal
size except for a protruding forehead.
aciclovir An antiviral drug that can be
taken by mouth, used topically, or given
intravenously to reduce the severity of
viral infections including herpes simplex
and herpes zoster. Local adverse reactions commonly occur after topical use.
Other side effects are uncommon but
can include nausea and vomiting.
acid A substance defined as a donor of
hydrogen ions (hydrogen atoms with
positive electrical charges). Acid molecules, when mixed with or dissolved in
water, split up to release their constituent ions; all acids release hydrogen
as the positive ion. (See also acid–base
balance; alkali.)
acid–base balance A combination of
mechanisms that ensures that the body’s
fluids are neither too acid nor too alkaline (alkalis are also called bases).
The body has three mechanisms for
maintaining normal acid–base balance:
buffers, breathing, and the activities of
the kidneys. Buffers are substances in
the blood that neutralize acid or alkaline wastes. Rapid breathing results in
the blood becoming less acidic; slow
breathing has the opposite effect. The
kidneys regulate the amounts of acid or
alkaline wastes in the urine.

Oesophageal dilatation allows the

oesophagus to be
widened for long
periods. Surgery to
cut some of the
muscles at the stomach entrance may
be necessary.
Achilles
Achilles tendon
tendon
The tendon that
raises the heel.
The Achilles tendon is formed from
the calf muscles
(gastrocnemius,
Heel
soleus, and plantar muscles) and
is attached to the
calcaneus (heel-bone). Minor injuries to
the Achilles tendon are common and
can result in inflammation (tendinitis).
Calf
muscle

8

ACIDOSIS

ACOUSTIC NEUROMA

Disturbances of the body’s acid–base
balance result in either acidosis (excessive blood acidity) or alkalosis (excessive
blood alkalinity).
acidosis A disturbance of the body’s
acid–base balance in which there is an
accumulation of acid or loss of alkali
(base). There are 2 types of acidosis:
metabolic and respiratory.
One form of metabolic acidosis is
ketoacidosis, which occurs in uncontrolled diabetes mellitus and starvation.
Metabolic acidosis may also be caused
by loss of bicarbonate (an alkali) as a
result of severe diarrhoea. In kidney failure, there is insufficient excretion of
acid in the urine.
Respiratory acidosis occurs if breathing
fails to remove enough carbon dioxide
from the lungs. The excess carbon dioxide remains in the bloodstream,
where it dissolves to form carbonic acid.
Impaired breathing leading to respiratory acidosis may be due to chronic
obstructive pulmonary disease (see pulmonary disease, chronic obstructive),
bronchial asthma, or airway obstruction.
acid reflux Regurgitation of acidic fluid
from the stomach into the oesophagus
due to inefficiency of the muscular valve
at the lower end of the oesophagus.
Also known as gastro-oesophageal
reflux disease (GORD), acid reflux may
inflame the oesophagus, resulting in
heartburn due to oesophagitis. It may
occur in pregnancy and often affects
overweight people.
acne A chronic skin disorder caused by
inflammation of the hair follicles and
sebaceous glands in the skin. The most
common type is acne vulgaris, which
almost always develops during puberty.
Acne spots are caused by the obstruction of hair follicles by sebum (the oily
substance secreted by the sebaceous
glands). Bacteria multiply in the follicle,
causing inflammation. The change in
sebum secretion at puberty seems to be
linked with increased levels of androgen
hormones (male sex hormones).
Acne may be brought on or aggravated
by drugs such as corticosteroids and
androgens. Exposure to certain chemicals and oils in the workplace can also
cause a type of acne.

A

Acne develops in areas of skin with a
high concentration of sebaceous glands,
mainly the face, centre of the chest,
upper back, shoulders, and around the
neck. Milia (whiteheads), comedones
(blackheads), nodACNE
ules (firm swellings beneath the Sebaceous Inflamed skin
skin), and cysts gland
Plug
(larger, fluid-filled
Pus
swellings) are the Hair
most commonly
occurring spots.
Some, particularly
cysts, leave scars
after they heal.
There is no instant cure for acne,
but washing the
affected areas at
least twice daily
may help to keep
ACNE SPOT
it under control.
Topical drug treatments, such as benzoyl peroxide or
retinoic acid, unblock the pores and
promote healing. Ultraviolet light can
be beneficial. If topical treatment has
failed, oral drug treatment with antibiotics, hormones, or isotretinoin may be
given. Acne improves slowly over time,
often clearing up by the end of the
teenage years.
acoustic nerve The part of the vestibulocochlear nerve (the 8th cranial nerve)
that is concerned with hearing. It is also
known as the auditory nerve.
acoustic neuroma A rare, noncancerous tumour arising from supporting
cells that surround the 8th cranial nerve
(see acoustic nerve), usually within the
internal auditory meatus (the canal in
the skull through which the nerve passes from the inner ear to the brain).
Usually, the cause of an acoustic neuroma is unknown. However, tumours that
affect the nerves on both sides of the
head simultaneously may be part of a
condition known as neurofibromatosis.
Acoustic neuroma can cause deafness,
tinnitus, loss of balance, and pain in the
face and the affected ear.
Diagnosis is made by hearing tests followed by X-rays, CT scanning, or MRI.
Surgery may be needed, but treatment
9

A

ACROCYANOSIS

ACTINOMYCOSIS

with radiotherapy to shrink the tumour
is also effective.
acrocyanosis A circulatory disorder in
which the hands and feet turn blue, may
become cold, and sweat excessively.
Acrocyanosis is caused by spasm of the
small blood vessels and is often aggravated by cold weather. It is related to
Raynaud’s disease.
acrodermatitis enteropathica A rare
inherited disorder in which areas of the
skin (most commonly the fingers, toes,
scalp, and the areas around the anus
and mouth) are reddened, ulcerated, and
covered with pustules. Acrodermatitis
enteropathica is due to an inability to
absorb enough zinc from food. Zinc
supplements usually help.
acromegaly A rare disease characterized
by abnormal enlargement of the skull,
jaw, hands, feet, and also of the internal
organs. It is caused by excessive secretion of growth hormone from the
anterior pituitary gland at the base of
the brain and is the result of a pituitary
tumour. A tumour that develops before
puberty results in gigantism. Acromegaly is diagnosed by measuring blood
levels of growth hormone, followed by
CT scanning or MRI.
acromioclavicular joint The joint that
lies between the outer end of the clavicle (collarbone) and the acromion
(the bony prominence at the top of the
scapula (shoulderblade).

acroparaesthesia A medical term used
to describe tingling in the fingers or
toes (see pins-and-needles).
ACTH The common abbreviation for
adrenocorticotrophic hormone (also
called corticotrophin). ACTH is produced
by the anterior pituitary gland and stimulates the adrenal cortex (outer layer of
the adrenal glands) to release various
corticosteroid hormones, most importantly hydrocortisone (cortisol) but also
aldosterone and androgen hormones.
ACTH production is controlled by a
feedback mechanism involving both the
hypothalamus and the level of hydrocortisone in the blood. ACTH levels
increase in response to stress, emotion,
injury, infection, burns, surgery, and
decreased blood pressure.
A tumour of the pituitary gland can
cause excessive ACTH production which
leads to overproduction of hydrocortisone by the adrenal cortex, resulting in
Cushing’s syndrome. Insufficient ACTH
production results in decreased production of hydrocortisone, causing low
blood pressure. Synthetic ACTH is occasionally given by injection to treat
arthritis or allergy.
actin A protein involved in muscle contraction, in which microscopic filaments
of actin and another protein, myosin,
slide in between each other.
acting out Impulsive actions that may
reflect unconscious wishes. The term is
most often used by psychotherapists
to describe behaviour during analysis
when the patient “acts out” rather than
reports fantasies, wishes, or beliefs.
Acting out can also occur as a reaction
to frustrations encountered in everyday
life, often taking the form of antisocial,
aggressive behaviour.
actinic Pertaining to changes caused by
the ultraviolet rays in sunlight, as in
actinic dermatitis (inflammation of the
skin) and actinic keratosis (roughness
and thickening of the skin).
actinomycosis An infection caused by
ACTINOMYCES ISRAELII or related actinomycete bacteria. The most common
form of actinomycosis affects the jaw
area. A painful swelling appears and
pus discharges through small openings
that develop in the skin. Another form

ACROMIOCLAVICULAR JOINT
Clavicle

Acromioclavicular
joint
Acromion

Scapula

Humerus

acromion A bony prominence at the
top of the scapula (shoulderblade). The
acromion articulates with the end of
the clavicle (collarbone) to form the
acromioclavicular joint.
10

ACUITY, VISUAL

ADENOCARCINOMA

of actinomycosis affects the pelvis in
women, causing lower abdominal pain
and bleeding between periods. This
form was associated with a type of IUD,
no longer in use, that did not contain
copper. Rarely, forms of the disorder
affect the appendix or lung. Actinomycosis is treated with antibiotics.
acuity, visual See visual acuity.
acupressure A derivative of acupuncture in which pressure is applied
instead of needles.
acupuncture A branch of Chinese medicine in which needles are inserted into
a patient’s skin as therapy for various
disorders or to induce anaesthesia.
Traditional Chinese medicine maintains that the chi (life-force) flows
through the body along channels called
meridians. A blockage in one or more of
these meridians is thought to cause ill
health. Acupuncturists aim to restore
health by inserting needles at appropriate sites along the affected meridians.
The needles are stimulated by rotation
or by an electric current. Acupuncture
has been used successfully as an anaesthetic for surgical procedures and to
provide pain relief after operations and
for chronic conditions.
acute A term often used to describe a
disorder or symptom that develops suddenly. Acute conditions may or may not
be severe, and they are usually of short
duration. (See also chronic.)
Adam’s apple A projection at the front
of the neck, just beneath the skin, that
is formed by a prominence on the thyroid cartilage, which is part of the larynx
(voice box). The Adam’s apple enlarges
in males at puberty.
ADD The abbreviation for attention deficit disorder, more commonly known as

the corticosteroid hormones hydrocortisone and aldosterone, normally produced
by the adrenal cortex (the outer part of
the adrenal glands). Excessive amounts
of ACTH are secreted by the pituitary
gland in an attempt to increase output
of the corticosteroid hormones. Secretion and activity of another hormone,
melanocyte stimulating hormone (MSH),
is also increased.
Addison’s disease can be caused by
any disease that destroys the adrenal
cortices. The most common cause is an
autoimmune disorder in which the
immune system produces antibodies
that attack the adrenal glands.
Symptoms generally develop gradually over months or years, and include
tiredness, weakness, abdominal pain,
and weight loss. Excess MSH may cause
darkening of the skin in the creases of
the palms, pressure areas of the body,
and the mouth. Acute episodes, called
Addisonian crises, brought on by infection, injury, or other stresses, can also
occur. The symptoms of these include
extreme muscle weakness, dehydration,
hypotension (low blood pressure), confusion, and coma. Hypoglycaemia (low
blood glucose) also occurs.
Life-long corticosteroid drug treatment
is needed. Treatment of Addisonian
crises involves rapid infusion of saline
and glucose, and supplementary doses
of corticosteroid hormones.
adduction Movement of a limb towards
the central line of the body, or of a digit
towards the axis of a limb. Muscles that
carry out this movement are often called
adductors. (See also abduction.)
adenitis Inflammation of lymph nodes.
Cervical adenitis (swelling and tenderness of the lymph nodes in the neck)
occurs in certain bacterial infections,
especially tonsillitis, and glandular fever
(see infectious mononucleosis). Mesenteric lymphadenitis is inflammation of
the lymph nodes inside the abdomen
and is usually caused by viral infection.
Treatment of adenitis may include analgesic drugs, and antibiotic drugs if there
is a bacterial infection.
adenocarcinoma The technical name
for a cancer of a gland or glandular tissue, or for a cancer in which the cells

attention deficit hyperactivity disorder.
addiction Dependence on, and craving
for, a particular drug, for example alcohol, diazepam (a tranquillizer), or heroin.
Reducing or stopping intake of the drug
may lead to characteristic physiological
or psychological symptoms (see withdrawal syndrome), such as tremor or
anxiety. (See also alcohol dependence;
drug dependence.)
Addison’s disease A rare chronic disorder in which there is a deficiency of
11

A

A

ADENOIDECTOMY

ADIPOSE TISSUE

form gland-like structures. An adenocarcinoma arises from epithelium (the
layer of cells that lines the inside of
organs). Cancers of the colon, breast,
pancreas, and kidney are usually adenocarcinomas, as are some cancers of the
cervix, oesophagus, salivary glands, and
other organs. (See also intestine, cancer
of; kidney cancer; pancreas, cancer of.)
adenoidectomy Surgical removal of the
adenoids. An adenoidectomy is usually
performed on a child with abnormally
large adenoids that are causing recurrent infections of the middle ear or air
sinuses. The operation may be performed together with tonsillectomy.
adenoids A mass of glandular tissue at
the back of the nasal passage above the
tonsils. The adenoids are made up of
lymph nodes, which form part of the
body’s defences against upper respiratory tract infections; they tend to
enlarge during early childhood, a time
when such infections are common.

organs). Adenomas of endocrine glands
can cause excessive hormone production, leading to disease. For example,
pituitary gland adenomas can result in
acromegaly or Cushing’s syndrome.
adenomatosis An abnormal condition
of glands in which they are affected
either by hyperplasia (overgrowth) or
the development of numerous adenomas
(noncancerous tumours). Adenomatosis may simultaneously affect 2 or more
different endocrine glands.
ADH The abbreviation for antidiuretic
hormone (also called vasopressin), which
is released from the posterior part of
the pituitary gland and acts on the kidneys to increase their reabsorption of
water into the blood. ADH reduces the
amount of water lost in the urine and
helps to control the body’s overall water
balance. ADH production is controlled
by the hypothalamus. Various factors
can affect ADH production and thus disturb the body’s water balance, including
drinking alcohol, the disorder diabetes
insipidus, or a major operation.
ADHD The abbreviation for attention
deficit hyperactivity disorder.
adhesion The joining of normally unconnected body parts by bands of fibrous
tissue. Adhesions are sometimes present from birth, but they most often
develop as a result of scarring after
inflammation. Adhesions are most common in the abdomen, where they often
form after peritonitis (inflammation of
the abdominal lining) or surgery. Sometimes, loops of intestine are bound
together by adhesions, causing intestinal obstruction (see intestine, obstruction
of). In such cases, surgery is usually
required to cut the bands of tissue.
adipose tissue A layer of fat just
beneath the skin and around various
internal organs. Adipose tissue is built
up from fat deposited as a result of
excess food intake, thus acting as an
energy store; excessive amounts of adipose tissue produce obesity. The tissue
insulates against loss of body heat and
helps absorb shock in areas subject to
sudden or frequent pressure, such as
the buttocks of feet.
In men, superficial adipose tissue accumulates around the shoulders, waist,

ADENOIDS
Adenoids
Nasal cavity

Opening of
eustachian
tube
Pharynx

Tongue
Tonsils

In most children, adenoids shrink after
the age of about 5 years, disappearing
altogether by puberty. In some children,
however, they enlarge, obstructing
breathing and blocking the eustachian
tubes, which connect the middle ear to
the throat. This results in recurrent
infections and deafness. Infections usually respond to antibiotic drugs, but if
they recur frequently, adenoidectomy
may be recommended.
adenoma A noncancerous tumour or
cyst that resembles glandular tissue
and arises from the epithelium (the
layer of cells that lines the inside of
12

ADJUVANT

ADRENAL GLAND DISORDERS

and abdomen; in women, it occurs on
the breasts, hips, and thighs.
adjuvant A substance that enhances
the action of another substance in the
body. The term is usually used to describe an ingredient added to a vaccine
to increase the production of antibodies
by the immune system, thus enhancing
the vaccine’s effect. Adjuvant chemotherapy is the use of anticancer drugs in
addition to surgical removal of a tumour.
Adlerian theory The psychoanalytical
ideas set forth by the Austrian psychiatrist Alfred Adler. Also called individual
psychology, Adler’s theories were based
on the idea that everyone is born with
feelings of inferiority. Life is seen as a
constant struggle to overcome these
feelings; failure to do so leads to neurosis. (See also psychoanalytic theory.)
adolescence The period between childhood and adulthood, which broadly
corresponds to the teenage years. Adolescence commences and overlaps with,
but is not the same as, puberty.
ADP The abbreviation for adenosine diphosphate, the chemical that takes up
energy released during biochemical reactions to form ATP (adenosine triphosphate), the body’s main energy-carrying
chemical. When ATP releases its energy,
ADP is reformed. (See also metabolism.)
adrenal failure Insufficient production
of hormones by the adrenal cortex (the
outer part of the adrenal glands). It can
be acute or chronic. Adrenal failure may
be caused by a disorder of the adrenal
glands, in which case it is called Addison’s disease, or by reduced stimulation
of the adrenal cortex by ACTH, a hormone produced by the pituitary gland.
adrenal glands A pair of small, triangular endocrine glands located above
the kidneys. Each adrenal gland has
2 distinct parts: the outer cortex and the
smaller, inner medulla.
The cortex secretes aldosterone, which,
together with hydrocortisone and corticosterone and small amounts of
androgen hormones helps to maintain
blood pressure. Hydrocortisone controls
the body’s use of fats, proteins, and carbohydrates and is also important in
helping the body to cope with stress.
Hydrocortisone and corticosterone also

suppress inflammatory reactions and
some activities of the immune system.
Production of adrenal cortical hormones is controlled by ACTH, which is
produced in the pituitary gland.
The adrenal medulla is part of the
sympathetic autonomic nervous system.
In response to stress, it secretes the
hormones adrenaline (epinephrine) and
noradrenaline (norepinephrine), which
increase heart-rate and blood flow.

A

ADRENAL GLANDS
Adrenal
gland
Kidney

Adrenal
cortex
Adrenal
medulla

LOCATION
Blood vessel

Kidney

STRUCTURE OF ADRENAL GLAND

adrenal gland disorders A range of
uncommon but sometimes serious disorders due to deficient or excessive
production of hormones by one or both
of the adrenal glands.
A genetic defect causes congenital
adrenal hyperplasia, in which the adrenal cortex is unable to make sufficient
hydrocortisone and aldosterone, and
androgens are produced in excess. In
adrenal failure, there is also deficient
production of hormones by the adrenal
cortex; if due to disease of the adrenal
glands, it is called Addison’s disease.
Adrenal tumours are rare and generally
lead to excess hormone production.
In many cases, disturbed activity of
the adrenal glands is caused, not by
disease of the glands themselves, but
by an increase or decrease in the blood
level of hormones that influence the
action of the adrenal glands. For example, hydrocortisone production by the
adrenal cortex is controlled by ACTH,
which is secreted by the pituitary gland.
Pituitary disorders can disrupt production of hydrocortisone.
13

Fat

A

ADRENAL HYPERPLASIA, CONGENITAL

AFFECT
phaeochromocytoma and neuroblastoma,

adrenal hyperplasia, congenital An
uncommon genetic disorder in which an
enzyme defect blocks the production
of corticosteroid hormones from the
adrenal glands. Excessive amounts of
androgens (male sex hormones) are produced, which can result in abnormal
genital development in an affected fetus.
Other effects include dehydration,
weight loss, low blood pressure, and
hypoglycaemia. Hyperplasia (enlargement) of the adrenal glands occurs and
there is excessive skin pigmentation in
skin creases and around the nipples.
In severe cases, the disorder is apparent soon after birth. In milder cases,
symptoms appear later, sometimes producing premature puberty in boys and
delayed menstruation, hirsutism, and
potential infertility in girls.
Congenital adrenal hyperplasia is confirmed by measuring corticosteroid
hormones in blood and urine. Treatment is by hormone replacement. If this
is started early, normal sexual development and fertility usually follow.
adrenaline A hormone, also called
epinephrine, released by the adrenal
glands in response to signals from the
sympathetic autonomic nervous system.
These signals are triggered by stress,
exercise, or by an emotion such as fear.
Adrenaline increases the speed and
force of the heartbeat. It widens the airways to improve breathing and narrows
blood vessels in the skin and intestine
so that an increased flow of blood
reaches the muscles.
Synthetic adrenaline is sometimes
given by injection as an emergency
treatment for cardiac arrest or anaphylactic shock. Adrenaline eye drops may
be used to treat glaucoma, but regular
use can cause a burning pain in the eye.
adrenal tumours Cancerous or noncancerous tumours in the adrenal
glands, usually causing excess secretion
of hormones. Adrenal tumours are rare.
Tumours of the adrenal cortex may
secrete aldosterone, causing primary
aldosteronism, or hydrocortisone, causing Cushing’s syndrome. Tumours of
the medulla may cause excess secretion
of adrenaline and noradrenaline. Two
types of tumour affect the medulla:

which affects children. These tumours
cause intermittent hypertension and
sweating attacks. Surgical removal of a
tumour usually cures these conditions.
adrenocorticotrophic hormone See
ACTH.
adrenogenital syndrome See adrenal
hyperplasia, congenital.
aerobic Requiring oxygen to live, function, and grow. Humans and many
other forms of life are dependent on
oxygen for “burning” foods to produce
energy (see metabolism). In contrast,
many bacteria thrive without oxygen
and are described as anaerobic.
aerobics Exercises, such as swimming
and cycling, that allow muscles to work
at a steady rate with a constant, adequate supply of oxygen-carrying blood,
and that can therefore be sustained for
long periods. Oxygen is used to release
energy from the body’s stores. To fuel
aerobic exercise, the muscles use fatty
acid, burning it completely to produce
energy, carbon dioxide, and water.
When performed regularly, aerobic
exercises improve stamina and endurance. They encourage the growth of
capillaries, improving blood supply to
the cells. Aerobic exercises also improve
body cells’ capacity to use oxygen and
increase the amount of oxygen the body
can use in a given time. The condition
of the heart also improves. (See also
exercise; fitness.)
aerodontalgia Sudden pain in a tooth
brought on by a change in surrounding
air pressure. Flying at a high altitude in
a lowered atmospheric pressure can
cause a pocket of air in the dental pulp
to expand and irritate the nerve in the
root. Aerodontalgia is more likely if
there are improperly fitting fillings or
poorly filled root canals.
aerophagy Excessive swallowing of air,
which may occur during rapid eating or
drinking or be caused by anxiety.
aetiology The cause of a disease or the
study of the various factors involved in
causing a disease.
affect A term used to describe a person’s mood. The 2 extremes of affect are
elation and depression. A person who
experiences extreme moods or changes
14

AFFECTIVE DISORDERS

AGGREGATION, PLATELET

in

moods may have an affective
disorder. Shallow or reduced affect may
be a sign of schizophrenia or of an
organic brain syndrome.
affective disorders Mental illnesses
characterized predominantly by marked
changes in affect. Mood may vary over a
period of time between mania (extreme
elation) and severe depression. (See
also manic–depressive illness.)
affinity A term used to describe the
attraction between chemicals that causes
them to bind together, as, for example,
between an antigen and an antibody
(see immune response). In microbiology,
affinity describes physical similarity
between organisms. In psychology, it
refers to attraction between 2 people.
aflatoxin A poisonous substance produced by ASPERGILLUS FLAVUS moulds,
which contaminate stored foods, especially grains, peanuts, and cassava.
Aflatoxin is believed to be one of the
factors responsible for the high incidence of liver cancer in tropical Africa.
afterbirth The common name for the
tissues that are expelled from the uterus
after delivery of a baby. The afterbirth
includes the placenta and the membranes that surrounded the fetus.
afterpains Contractions of the uterus
that continue after childbirth. Afterpains
are normal and are experienced by
many women, especially during breastfeeding. They usually disappear a few
days following the birth but may require
treatment with analgesic drugs.
agammaglobulinaemia A type of immunodeficiency disorder in which there
is almost complete absence of B-lymphocytes and immunoglobulins in the blood.
agar An extract of certain seaweeds
with similar properties to gelatine. It
can be taken for constipation to soften
and give bulk to faeces, and to relieve
indigestion and heartburn. Agar is also
used as a gelling agent in media for
bacterial cultures.
age The length of time a person has
existed. Of medical significance in diagnosis and in determining treatment, a
person’s age is usually measured
chronologically, but it can also be measured in terms of physical, mental, or
developmental maturity.

The age of a fetus is measured in terms
of gestational age, which can be
assessed accurately by ultrasound scanning. In children, the most useful
measure of physical development is
bone age (degree of bone maturity as
seen on an X-ray) because all healthy
individuals reach the same adult level
of skeletal maturity, and each bone
passes through the same sequence of
growth. Dental age, another measure
of physical maturity, can be assessed by
the number of teeth that have erupted
(see eruption of teeth) or by the amount
of dental calcification (as seen on an
X-ray) compared with standard values.
In adults, physical age is difficult to
assess other than by physical appearance. It can be estimated after death by
the state of certain organs.
Mental age can be assessed by comparing scores on intelligence tests with
standards for chronological age. A young
child’s age can be expressed in terms of
the level of developmental skills, manual dexterity, language, and social skills.
agenesis The complete absence at birth
of an organ or bodily component, caused
by failure of development in the embryo.
agent Any substance or force capable of
bringing about a biological, chemical, or
physical change. (See also reagent.)
Agent Orange A herbicide of which
the major constituent is the phenoxy
acid herbicide 2,4,5 T. This substance
may be contaminated in manufacture
with the highly toxic TCDD, commonly
known as dioxin (see defoliant poisoning).
age spots Blemishes that appear on the
skin with increasing age. Most common
are seborrhoeic keratoses, which are
brown or yellow, slightly raised spots
that can occur at any site. Also common
in elderly people are freckles, solar keratoses (small blemishes caused by
overexposure to the sun), and De Morgan’s spots, which are red, pinpoint
blemishes on the trunk. Treatment is
usually unnecessary for any of these,
apart from solar keratoses, which may
eventually progress to skin cancer.
ageusia The lack or an impairment of
the sense of taste (see taste, loss of).
aggregation, platelet The clumping
together of platelets (small, sticky blood
15

A

A

AGGRESSION

AGUE

alcohol withdrawal. Depression may be
accompanied by agitation.
agnosia An inability to recognize objects
despite adequate sensory information
about them reaching the brain via the
eyes or ears or through touch. Agnosia
is caused by damage to areas of the
brain that are involved in interpretative
and recall functions. The most common
causes of this kind of damage are stroke
or head injury.
Agnosia is usually associated with just
one of the senses of vision, hearing, or
touch and is described as visual, auditory, or tactile respectively. Some people,
after a stroke that damages the right
cerebral hemisphere, seem unaware of
any disability in their affected left limbs.
This is called anosognosia or sensory
inattention. There is no specific treatment for agnosia, but some interpretative
ability may return eventually.
agonist Having a stimulating effect. An
agonist drug, sometimes known as an
activator, is one that binds to a sensory
nerve cell (receptor) and triggers or increases a particular activity in that cell.
agoraphobia Fear of going into open
spaces or public places. Agoraphobia
(see phobia) may occur with claustrophobia. If sufferers do venture out, they
may have a panic attack, which may lead
to further restriction of activities. People with agoraphobia may eventually
become housebound. Treatment with
behaviour therapy is usually successful.
Antidepressant drugs may be helpful.
agraphia Loss of, or impaired, ability to
write, despite normal functioning of the
hand and arm muscles, caused by brain
damage. Agraphia can result from damage to any of the various parts of the
cerebrum concerned with writing and
can therefore be of different types and
degrees of severity. Such damage is most
commonly due to head injury, stroke, or
a brain tumour. Agraphia is often accompanied by alexia (loss of the ability to
read) or may be part of an expressive
aphasia (general disturbance in the
expression of language). There is no
specific treatment for agraphia, but some
lost writing skills may return in time.
ague An outdated term for malaria or
other diseases causing fever in which

particles). Aggregation is the 1st stage
of blood clotting and helps to plug
injured vessels. Inappropriate aggregation can have adverse effects; for
example, if aggregation occurs in an
artery, it may result in a thrombosis.
aggression A general term for a wide
variety of acts of hostility. A number of
factors, including human evolutionary
survival strategies, are thought to be
involved in aggression. Androgen hormones, the male sex hormones, seem to
promote aggression, whereas oestrogen
hormones, the female sex hormones,
actively suppress it. Age is another
factor; aggression is more common
among teenagers and young adults.
Sometimes, a brain tumour or head
injury leads to aggressive behaviour.
Psychiatric conditions associated with
aggressive outbursts are schizophrenia,
antisocial personality disorder, mania,
and abuse of amfetamines or alcohol.
Temporal lobe epilepsy, hypoglycaemia,
and confusion due to physical illnesses
are other, less common, medical causes.
aging The physical and mental changes
that occur with the passing of time.
Aging is associated with degenerative
changes in various organs and tissues,
such as loss of elasticity in the skin and
a progressive decline in organ function.
Mechanical wear and tear causes cumulative damage to the joints, and the
muscles lose bulk and strength. Wound
healing and resistance to infection also
decline. Gradual loss of nerve cells can
lead to reduced sensory acuity and difficulties with learning and memory.
However, dementia occurs in only a
minority of elderly people.
Heredity is an important determinant
of life expectancy, but physical degeneration may be accelerated by factors
such as smoking, excessive alcohol intake, poor diet, and insufficient exercise.
agitation Restless inability to keep still,
usually as a result of anxiety or tension.
Agitated people engage in aimless,
repetitive behaviour, such as pacing up
and down or wringing their hands, and
they often start tasks without completing them. Persistent agitation is seen
in anxiety disorders, especially if there is
an underlying physical cause such as
16

AIDS

AIR CONDITIONING
candidiasis (thrush), shingles, tuberculosis, and shigellosis. HIV may also affect

the sufferer alternately feels excessively
hot and shiveringly cold.
AIDS Acquired immune deficiency syndrome, a deficiency of the immune
system due to infection with HIV (human
immunodeficiency virus). In most countries, illness and death from AIDS is a
growing health problem, and there is,
as yet, no cure or vaccine.
AIDS does not develop in all people
infected with HIV. The interval between
infection and the development of AIDS
is highly variable. Without treatment,
around half of those people infected
will develop AIDS within 8–9 years.
HIV is transmitted in body fluids, including semen, blood, vaginal secretions,
and breast milk. The major methods of
transmission are sexual contact (vaginal, anal, or oral), blood to blood (via
transfusions or needle-sharing in drug
users), and mother to fetus. HIV has
also been transmitted through blood
products given to treat haemophilia, artificial insemination by donated semen,
and kidney transplants; but improved
screening has greatly reduced these
risks. HIV is not spread by everyday contact, such as hugging or sharing crockery.
The virus enters the bloodstream and
infects cells that have a particular receptor, known as the CD4 receptor, on their
surface. These cells include a type of
white blood cell (a CD4 lymphocyte)
responsible for fighting infection and
cells in other tissues such as the brain.
The virus reproduces within the infected
cells, which then die, releasing more
virus particles into the blood. If the
infection is left untreated, the number
of CD4 lymphocytes falls, resulting in
greater susceptibility to certain infections and some types of cancer.
Some people experience a short-lived
illness similar to infectious mononucleosis when they are first infected with
HIV. Many individuals have no obvious
symptoms; some have only vague complaints, such as weight loss, fevers,
sweats, or unexplained diarrhoea, described as AIDS-related complex.
Minor features of HIV infection include skin disorders such as seborrhoeic
dermatitis. More severe features include
persistent herpes simplex infections, oral

the brain, causing a variety of neurological disorders, including dementia.
Certain conditions, known as AIDSdefining illnesses, are characteristic of
full-blown AIDS. These include cancers
(Kaposi’s sarcoma and lymphoma of
the brain), and various infections (pneumocystis pneumonia, cytomegalovirus
infection, toxoplasmosis, diarrhoea due
to CRYPTOSPORIDIUM or ISOSPORA, candidiasis, disseminated strongyloidiasis, and
cryptococcosis), many of which are
described as opportunistic infections.
Confirmation of HIV infection involves
testing a blood sample for the presence
of antibodies to HIV. Diagnosis of fullblown AIDS is based on a positive HIV
test along with the presence of an AIDSdefining illness.
The risk of infection with HIV can be
reduced by practising safer sex. Intravenous drug users should not share
needles. There is a small risk to health
workers handling infected blood products or needles, but this risk can be
minimized by safe practices.
Treatment of HIV infection with a combination of antiviral drugs can slow the
disease’s progress, and may prevent
the development of full-blown AIDS. The
2 main types of antiviral drug used are
protease inhibitors, such as indinavir,
and reverse transcriptase inhibitors
such as zidovudine. Treatment is also
available for AIDS-defining illnesses.
AIDS-related complex A combination
of weight loss, fever, and enlarged lymph
nodes in a person who has been infected with HIV (the AIDS virus), but does
not have AIDS itself. Many people with
AIDS-related complex will eventually
develop the features of AIDS.
air The colourless, odourless mixture of
gases that forms the Earth’s atmosphere.
Air consists of 78 per cent nitrogen, 21
per cent oxygen, small quantities of
carbon dioxide and other gases, and
some water vapour.
air conditioning A system that controls
the purity, humidity, and temperature
of the air in a building. Contaminated
air-conditioning systems may cause legionnaires’ disease and humidifier fever
17

A

A

AIR EMBOLISM

ALCOHOL

(a lung disease causing coughing and
breathing difficulty).
air embolism Blockage of a small artery
by an air bubble carried in the blood.
Air embolism is rare. In most cases, it is
caused by air entering the circulation
through a vein, either due to injury or
surgery. Air embolism can also occur
during diving or air travel accidents, in
which lung tissue ruptures, releasing
bubbles into the bloodstream.
air pollution See pollution.
air swallowing See aerophagy.
airway A collective term for the passages through which air enters and
leaves the lungs (see respiratory system). The term is also applied to a tube
inserted into the mouth of an unconscious person to prevent the tongue
from obstructing breathing.
airway obstruction Narrowing or blockage of the respiratory passages. The
obstruction may be due to a foreign
body, such as a piece of food, that
becomes lodged in part of the upper
airway and may result in choking. Certain disorders, such as diphtheria and
lung cancer, can cause obstruction.
Additionally, spasm of the muscular
walls of the airway, as occurs in bronchospasm (a feature of asthma), results
in breathing difficulty.
akathisia An inability to sit still, occasionally occurring as a side effect of an
antipsychotic drug or, less commonly, as
a complication of Parkinson’s disease.
akinesia Complete or almost complete
loss of movement. It may be a result of
damage to part of the brain due, for example, to a stroke or Parkinson’s disease.
albinism A rare genetic disorder characterized by a lack of the pigment melanin,
which gives colour to the skin, hair, and
eyes. In oculocutaneous albinism (the
most common type), the hair, skin, and
eyes are all affected. Less often, only
the eyes are affected. In both forms,
skin cannot tan and ages prematurely,
and skin cancers may develop on areas
exposed to the sun. Visual problems of
people with albinism include photophobia, nystagmus, squint, and myopia.
Glasses are usually needed from an
early age; and tinted glasses help to
reduce photophobia.

albumin The most abundant protein in
the blood plasma. Albumin is made in
the liver from amino acids. It helps to
retain substances (such as calcium,
some hormones, and certain drugs) in
the circulation by binding to them to
prevent them from being filtered out by
the kidneys and excreted. Albumin also
regulates the movement of water between tissues and the bloodstream by
osmosis. (See also albuminuria.)
albuminuria The presence of the protein albumin in the urine; a type of
proteinuria. Normally, the glomeruli (the
filtering units of the kidneys) do not
allow albumin to pass into the urine.
Albuminuria therefore usually indicates
that there is damage to the kidneys’
filtering mechanisms. Such damage
may be due to a kidney disorder, such
as glomerulonephritis or nephrotic syndrome, or may be a sign that the kidneys
have been affected by hypertension.
Albuminuria can be detected by a simple urine test.
alcohol A colourless liquid produced
from the fermentation of carbohydrates
by yeast. Also known as ethanol, alcohol is the active constituent of drinks
such as beer and wine. In medicine, it is
used as an antiseptic and solvent. Methanol is a related, highly toxic substance.
Alcohol is a drug and produces a wide
range of mental and physical effects.
The effect of alcohol on the central
nervous system is as a depressant,
decreasing its activity and thereby
reducing anxiety, tension, and inhibitions. In moderate amounts, alcohol
produces a feeling of relaxation, confidence, and sociability. However, alcohol
slows reactions, and the more that is
drunk, the greater is the impairment of
concentration and judgement. Excessive consumption of alcohol results in
poisoning or acute alcohol intoxication,
with effects ranging from euphoria to
unconsciousness.
Short-term physical effects of alcohol
include peripheral vasodilation (widening of the small blood vessels), which
causes the face to flush, and increased
flow of gastric juices, which stimulates
the appetite. Alcohol increases sexual
confidence, but high levels can cause
18

ALCOHOL DEPENDENCE

ALCOHOL INTOXICATION

tingling; weakness in the legs and
hands; irregular pulse; enlarged blood
vessels in the face; unsteadiness; confusion; memory lapses; and incontinence.
After sudden withdrawal from alcohol,
delirium tremens may occur.
Alcohol-dependent persons are more
susceptible than others to a variety of
physical and mental disorders (see
alcohol-related disorders).
Many alcoholics require detoxification
followed by long-term treatment. Different methods of treatment may be
combined. Psychological treatments involve psychotherapy and are commonly
carried out as group therapy. Social
treatments may offer practical help and
tend to include family members in the
process. Physical treatment generally
includes the use of disulfiram, a drug
that sensitizes the drinker to alcohol so
that he or she experiences unpleasant
side effects when drinking. Alcoholics
Anonymous and other self-help organizations can provide support and advice.
Alcoholics Anonymous A worldwide,
independent, self-help organization that
is operated locally by people working
on a voluntary basis to overcome alcohol dependence. Regular group meetings
are held in which members are encouraged to help one another stay sober by
sharing their experiences openly and
offering support and advice.
alcohol intoxication The condition that
results from consuming an excessive
amount of alcohol, often over a relatively short period. The effects of a large
alcohol intake depend on many factors,
including physical and mental state,
body size, social situation, and acquired
tolerance. The important factor, however, is the blood alcohol level. Mild
intoxication promotes relaxation and
increases social confidence. Alcohol
causes acute poisoning if taken in sufficiently large amounts, however. It
depresses the activity of the central nervous system, leading to loss of normal
mental and physical control. In extreme
cases, intoxication may lead to loss of
consciousness and even death.
In most cases, recovery from alcohol
intoxication takes place naturally as
the alcohol is gradually broken down in

impotence. Alcohol also acts as a

diuretic, increasing urine output.
In the long term, regular excessive
alcohol consumption can cause gastritis
(inflammation and ulceration of the
stomach lining), and lead to alcoholrelated disorders. Heavy drinking in
the long term may also lead to alcohol
dependence. However, people who drink
regular, small amounts of alcohol (an
average of 1–2 units a day) seem to
have lower rates of coronary heart disease and stroke than total abstainers.
alcohol dependence An illness characterized by habitual, compulsive, longterm, heavy consumption of alcohol and
the development of withdrawal symptoms when drinking is suddenly stopped.
Three causative factors interact in the
development of the illness: personality,
environment, and the addictive nature
of alcohol. Inadequate, insecure, or
immature personalities are more at risk.
Environmental factors are important,
especially the ready availability, affordability, and social acceptance of alcohol.
Genetic factors may play a part in causing dependence in some cases, but it is
now widely believed that anyone, irrespective of personality, environment, or
genetic background, can become an
alcoholic. Stress is often a major factor
in precipitating heavy drinking.
Alcohol dependence usually develops
in 4 main stages that occur over a number of years. In the 1st phase, tolerance
to alcohol develops in the heavy social
drinker. In the 2nd phase, the drinker
experiences memory lapses relating to
events during the drinking episodes. In
the 3rd phase, there is loss of control
over alcohol consumption. The final
phase is characterized by prolonged
binges of intoxication and mental or
physical complications.
Behavioural symptoms are varied and
can include furtive, aggressive, or grandiose behaviour; personality changes
(such as irritability, jealousy, or uncontrolled anger); neglect of food intake
and personal appearance; and lengthy
periods of intoxication.
Physical symptoms may include nausea, vomiting, or shaking in the morning;
abdominal pain; cramps; numbness or
19

A

A

ALCOHOLISM

ALEXIA

the liver. Medical attention is required
if the intoxication has resulted in
coma. For the chronic mental, physical,
and social effects of long-term heavy
drinking, see alcohol dependence and
alcohol-related disorders.
alcoholism See alcohol dependence.
alcohol-related disorders A wide variety of physical and mental disorders
associated with heavy, prolonged consumption of alcohol.
High alcohol consumption increases
the risk of cancers of the mouth, tongue,
pharynx (throat), larynx (voice box), and
oesophagus, especially if combined with
smoking. Incidence of liver cancer, as
well as the liver diseases alcoholic hepatitis and cirrhosis, is higher among
alcoholics. High alcohol consumption
increases the risk of cardiomyopathy,
hypertension, and stroke. Alcohol irritates the digestive tract and may cause
gastritis. Heavy drinking in pregnancy
increases the risk of miscarriage and
fetal alcohol syndrome. Alcoholics are
more likely to suffer from anxiety and
depression and to develop dementia.
Many alcoholics have a poor diet and
are prone to diseases caused by nutritional deficiency, particularly of thiamine
(see vitamin B complex). Severe thiamine deficiency, called beriberi, disturbs
nerve function, causing cramps, numbness, and weakness in the legs and
hands. Its effects on the brain can cause
confusion, disturbances of speech and
gait, and eventual coma (see Wernicke–
Korsakoff syndrome). Severe thiamine
deficiency can also cause heart failure.
A prolonged high level of alcohol in
the blood and tissues can disturb body
chemistry, resulting in hypoglycaemia
(reduced glucose in the blood) and
hyperlipidaemia (increased fat in the
blood). These may damage the heart,
liver, blood vessels, and brain; irreversible damage may cause premature death.
aldosterone A hormone secreted by
the adrenal cortex (the outer part of the
adrenal glands). Aldosterone acts on the
kidneys to regulate the concentrations
of sodium and potassium in the blood
and tissues and control blood pressure.
Production of aldosterone is stimulated
mainly by the action of angiotensin II, a

chemical produced by a series of reactions involving the enzymes renin and
angiotensin-converting enzyme. Aldosterone production is also stimulated by
the action of ACTH, which is produced
by the pituitary gland.
aldosteronism A disorder that results
from the excessive production of the
hormone aldosterone from one or both
adrenal glands. Aldosteronism caused
by an adrenal tumour is known as
Conn’s syndrome. Aldosteronism may
also be caused by disorders, such as
heart failure or liver damage, that reduce
the flow of blood through the kidneys.
Reduced blood flow through the kidneys leads to overproduction of renin
and angiotensin, which, in turn, leads to
excessive aldosterone production.
Symptoms are directly related to the
actions of aldosterone. Too much sodium
is retained in the body, leading to a rise
in blood pressure, and excess potassium
is lost in the urine. Low potassium causes tiredness and muscle weakness and
impairs kidney function, leading to thirst
and overproduction of urine.
Treatment in all cases includes restriction of dietary salt and use of the
diuretic drug spironolactone. If the cause
of aldosteronism is an adrenal tumour,
this may be surgically removed.
alendronate sodium See alendronic
acid.
alendronic acid A bisphosphonate drug
used in the treatment of osteoporosis
and Paget’s disease of bone. The most
common side effect is inflammation of
the oesophagus, which causes heartburn or difficulty in swallowing. Other
side effects can include headache and
abdominal pain.
Alexander technique A therapy that
aims to improve health by teaching people to stand and move more efficiently.
The technique is based on the belief
that bad patterns of body movement
interfere with the proper functioning of
the body and contribute to the development of disease.
alexia Word blindness; inability to recognize and name written words. Alexia
is caused by damage to part of the cerebrum (the main mass of the brain) by a
stroke, for example. It severely disrupts
20

ALIENATION

ALLERGY

the reading ability of a person who was
previously literate. (See also dyslexia.)
alienation Feeling like a stranger, even
when among familiar people or places,
and being unable to identify with a culture, family, or peer group. Alienation is
common in adolescents and also occurs
in people who are isolated by cultural
or language differences. In some people,
it may be an early symptom of schizophrenia or a personality disorder.
alignment, dental The movement of
teeth by using either fixed or removable
orthodontic appliances (braces) to correct malocclusion (incorrect bite).
alimemazine An antihistamine drug, also
known as trimeprazine, that is used
mainly to relieve itching in allergic conditions such as urticaria and atopic
eczema. Alimemazine often causes
drowsiness.
alimentary tract The tube-like structure that extends from the mouth to the
anus (see digestive system).
alkali Also known as a base, an alkali is
chemically defined as a donor of hydroxyl
ions (each of which comprises an atom
of hydrogen linked to an atom of oxygen
and has an overall negative electrical
charge). Antacid drugs, such as sodium
bicarbonate, are alkalis. Some alkalis,
such as sodium hydroxide, are corrosive. (See also acid; acid–base balance.)
alkaloids A group of nitrogen-containing
substances obtained from plants. Morphine, codeine, nicotine, and strychnine
(see strychnine poisoning) are examples.
alkalosis A disturbance of the body’s
acid–base balance in which there is an
accumulation of alkali or a loss of acid.
There are 2 types: metabolic and respiratory. In metabolic alkalosis, the
increase in alkalinity may be caused by
taking too much of an antacid drug or
by losing a large amount of stomach
acid as a result of severe vomiting. In
respiratory alkalosis, there is a reduction in the blood level of carbonic acid
(derived from carbon dioxide). This
reduction is a consequence of hyperventilation, which may occur during a
panic attack or at high altitudes due to
lack of oxygen. (See also acidosis.)
alkylating agents A class of anticancer
drugs.

allele One of 2 or more different forms of
a gene that occupies a specific position
on a chromosome (see gene; inheritance).
allergen A normally harmless substance
that causes an allergic reaction (see
allergy) in people who have become
sensitized to it. Allergens can include
foods (for example, nuts, eggs, and shellfish); inhaled substances such as pollen,
house dust, and fur; and some drugs.
allergy Various conditions caused by
inappropriate or exaggerated reactions
of the immune system (known as hypersensitivity reactions) to a variety of
substances. Many common illnesses,
such as asthma and allergic rhinitis (hay
fever), are caused by allergic reactions
to substances that in the majority of
people cause no symptoms.
Allergic reactions occur only on 2nd or
subsequent exposure to the allergen,
once 1st contact has sensitized the body.
The function of the immune system is
to recognize antigens (foreign proteins)
on the surfaces of microorganisms and
to form antibodies (also called immunoglobulins) and sensitized lymphocytes
(white blood cells). When the immune
system next encounters the same antigens, the antibodies and sensitized
lymphocytes interact with them, leading
to destruction of the microorganisms.
A similar immune response occurs in
allergies, except that the immune system
forms antibodies or sensitized lymphocytes against harmless substances
because these allergens are misidentified as potentially harmful antigens.
The inappropriate or exaggerated reactions seen in allergies are termed

A

ALLERGY
Allergen
Mast cell

Antibody
attaches to
mast cell

Histamine
Allergen
binds to
antibody

Histamine
released

Nucleus

TYPE I HYPERSENSITIVITY
21

A

ALLOPATHY

ALOPECIA

hypersensitivity reactions and can have

reactions to specific allergens such as
bee stings. Treatment involves gradually increasing doses of the allergen,
but it must be carried out under close
supervision because a severe allergic
reaction can result.
allopathy The practice of conventional
medicine. (See also homeopathy.)
allopurinol A drug treatment for gout.
Taken long term, it reduces the frequency of attacks by decreasing production
of uric acid. Possible adverse reactions
include itching, rashes, and nausea.
alopecia Loss or absence of hair, which
may occur at any hair-bearing site on
the body but which is usually noticeable only on the scalp.
Male-pattern baldness, the most common form of alopecia, is hereditary and
most often affects men. Normal hair is
lost initially from the temples and
crown and is replaced by fine, downy
hair; the affected area gradually widens.
Other hereditary forms are rare. They
may be due to an absence of hair roots
or abnormalities of the hair shaft.
In generalized alopecia, the hair falls
out in large amounts. Causes include
various forms of stress, such as surgery,
prolonged illness, or childbirth. Many
anticancer drugs cause temporary alopecia. The hair regrows when the
underlying cause is corrected.
Localized alopecia may be due to permanent skin damage (for example, by
burns or radiotherapy) or trauma to
the hair roots by styling or, rarely,
trichotillomania (a disorder in which sufferers pull out their hair). The most
common type of localized hair loss is
alopecia areata, which is an autoimmune disorder. There is no specific
treatment, but the hair usually regrows
within a few months. Alopecia universalis is a rare, permanent form of
alopecia areata that causes loss of all the
hair on the scalp and body, including
the eyelashes and eyebrows. Skin diseases such as scalp ringworm (see
tinea), lichen planus, lupus erythematosus, and skin tumours may also cause
localized hair loss.
Treatments for male-pattern baldness
include hair transplants or drug treatments with minoxidil or finasteride.

any of four different mechanisms (termed
Types I to IV hypersensitivity reactions).
Most well known allergies are caused by
Type I (also known as anaphylactic or
immediate) hypersensitivity in which
allergens cause immediate symptoms
by provoking the immune system to
produce specific antibodies, belonging
to a type called immunoglobulin E
(IgE), which coat cells (called mast cells
or basophils). When the allergen is
encountered for the second time, it
binds to the IgE antibodies and causes
the granules in mast cells to release
various chemicals, which are responsible for the symptoms of the allergy.
Among the chemicals released is histamine, which causes widened blood
vessels, leakage of fluid into tissues, and
muscle spasm. Symptoms can include
itching, swelling, sneezing, and wheezing. Particular conditions associated
with Type I reactions include asthma,
hay fever, urticaria (nettle rash), angioedema, anaphylactic shock (a severe,
generalized allergic reaction), possibly
atopic eczema, and many food allergies.
Types II to IV hypersensitivity reactions are less often implicated in
allergies. However, contact dermatitis,
in which the skin reacts to substances
such as nickel, is due to a Type IV hypersensitivity reaction.
It is not known why certain individuals
and not others get allergies, but about
1 in 8 people seem to have an inherited
predisposition to them (see atopy).
Whenever possible, the most effective
treatment for allergy of any kind is
avoidance of the relevant allergen.
Drug treatment for allergic reactions
includes the use of antihistamine drugs,
which relieve the symptoms. Some antihistamine drugs have a sedative effect,
which is useful in treating itching at
night due to eczema. Many antihistamines do not cause drowsiness, making
them more suitable for daytime use.
Other drugs, such as sodium cromoglicate and corticosteroid drugs, can be
used regularly to prevent symptoms
from developing.
Hyposensitization can be valuable for a
minority of people who suffer allergic
22

ALPHA 1 -ANTITRYPSIN DEFICIENCY

ALVEOLITIS

alpha1-antitrypsin deficiency A rare
genetic disorder in which a person is
missing the enzyme alpha1-antitrypsin,
which protects the body from damage
by other enzymes. The disease mainly
affects tissues in the lungs, resulting in
emphysema, and the liver, causing cirrhosis. The effects of alpha1-antitrypsin
deficiency may not become apparent
until after the age of 30. There is no
cure, but symptoms can be relieved by
drug treatment. In severe cases, a liver
transplant may be a possibility.
alpha-blocker drugs A group of drugs
used to treat hypertension (high blood
pressure) and urinary symptoms due to
enlargement of the prostate gland.
Alpha-blockers are also used to treat
urinary retention caused by an enlarged
prostate gland (see prostate, enlarged).
Side effects of the drugs may include
dizziness and fatigue due to a sudden
drop in blood pressure, nausea, dry
mouth, and drowsiness.
alpha-fetoprotein A protein that is
produced in the liver and gastrointestinal tract of the fetus and by some
abnormal tissues in adults.
Alpha-fetoprotein (AFP) can be measured in the maternal blood from the
latter part of the 1st trimester of pregnancy, and its concentration rises
between the 15th and 20th weeks.
Raised levels of AFP are associated with
fetal neural tube defects, such as spina
bifida or anencephaly, and certain kidney abnormalities. High levels of AFP
also occur in multiple pregnancies (see
pregnancy, multiple) and threatened or
actual miscarriage. AFP levels may be
unusually low if the fetus has Down’s
syndrome. For this reason, measurement of blood AFP is included in blood
tests, which are used to screen pregnant women for an increased risk of
Down’s syndrome.
AFP levels are commonly raised in
adults with hepatoma (see liver cancer),
cancerous teratoma of the testes or
ovaries, or cancer of the pancreas,
stomach, or lung. For this reason, AFP
is known as a tumour marker. AFP levels
can be used to monitor the results of
treatment of certain cancers; increasing
levels after surgery or chemotherapy

may indicate tumour recurrence. However, AFP levels are also raised in some
noncancerous conditions, including viral
and alcoholic hepatitis and cirrhosis.
alprazolam A benzodiazepine drug used
in the treatment of anxiety, panic attacks,
and phobias.
alprostadil A prostaglandin drug used,
prior to surgery, to minimize the effects
of congenital heart defects in newborn
babies. Alprostadil is also used as a
treatment for impotence. It is administered by self-injection into the penis or
as a gel introduced into the urethra to
produce an erection.
alternative medicine Any medical system based on a theory of disease or
method of treatment other than the
orthodox science of Western medicine.
(See also complementary medicine.)
altitude sickness See mountain sickness.
aluminium A light, metallic element
found in bauxite and various other minerals. Aluminium compounds are used
in antacid medications and in antiperspirants. Most of the aluminium taken
into the body is excreted. Excessive
amounts are toxic and are stored in the
lungs, brain, liver, and thyroid gland,
where they may result in organ damage.
Certain industrial processes give off
fumes containing aluminium into the
air. These fumes can cause fibrosis of
lung tissue. Drugs that contain aluminium may interfere with the absorption
of other drugs and, therefore, should
not be taken at the same time.
alveolectomy See alveoloplasty.
alveolitis Inflammation and thickening
of the walls of the alveoli (tiny air sacs)
in the lungs. Alveolitis reduces the elasticity, and therefore the efficiency, of the
lungs. It is most commonly due to an
allergic reaction to inhaled dust of animal or plant origin, as in farmer’s lung,
bagassosis, and pigeon fancier’s lung
(due to particles from bird droppings).
Fibrosing alveolitis is an autoimmune
disorder. In some cases, it occurs with
other autoimmune disorders such as
rheumatoid arthritis or systemic lupus
erythematosus. Radiation alveolitis is
caused by irradiation of the lungs and
may occur as a rare complication of
radiotherapy for lung or breast cancer.
23

A

A

ALVEOLOPLASTY

AMAUROSIS FUGAX

Alveolitis usually causes a dry cough
and breathing difficulty on exertion. A
chest X-ray, blood tests, pulmonary
function tests, or a lung biopsy may be
needed to diagnose alveolitis.
For most types of alveolitis, a short
course of corticosteroid drugs relieves
symptoms, but for fibrosing alveolitis
these may need to be taken indefinitely.
If the cause of allergic alveolitis is recognized and avoided before lung damage
occurs, the effects are not permanent.
In fibrosing alveolitis, damage progresses
despite treatment, causing increasing
breathing difficulty and, sometimes,
respiratory failure.
alveoloplasty Dental surgery to remove
protuberances and smooth out uneven
areas from tooth-bearing bone in the
jaw before the fitting of dentures.
alveolus, dental The bony cavity or
socket supporting each tooth in the jaw.
alveolus, pulmonary One of a large
number of tiny, balloon-like sacs at the
end of a bronchiole (one of many small
air passages in the lungs) where gases
are exchanged during respiration.

are responsible for the production of
the blood protein apolipoprotein E.
These genes also result in the deposition of a protein called beta amyloid
in the brain. Other chemical abnormalities may include deficiency of the
neurotransmitter acetylcholine.
The features of Alzheimer’s disease
vary, but there are 3 broad stages. At
first, the person becomes increasingly
forgetful, and problems with memory
may cause anxiety and depression. In
the 2nd stage, loss of memory, particularly for recent events, gradually
becomes more severe, and there may
be disorientation as to time or place.
The person’s concentration and numerical ability decline, and there is
noticeable dysphasia (inability to find
the right word). Anxiety increases,
mood changes are unpredictable, and
personality changes may occur. Finally,
confusion becomes profound. There
may be symptoms of psychosis, such as
hallucinations and delusions. Signs of
nervous system disease, such as abnormal reflexes and faecal or urinary
incontinence, begin to develop.
Alzheimer’s disease is usually diagnosed from the symptoms, but tests
including blood tests and CT scanning
or MRI of the brain may be needed to
exclude treatable causes of dementia.
The most important aspect of treatment for Alzheimer’s disease is the
provision of suitable nursing and social
care for sufferers and support for their
relatives. Tranquillizer drugs can often
improve difficult behaviour and help
with sleep. Treatment with drugs such
as donepezil and rivastigmine may slow
the progress of the disease for a time,
but side effects such as nausea and
dizziness may occur.
amalgam, dental A material, consisting of an alloy of mercury with other
metals, that is used as fillings for teeth
(see filling, dental).
amantadine An antiviral drug used in
the prevention and treatment of influenza A and to help relieve symptoms of
Parkinson’s disease.
amaurosis fugax Brief loss of vision,
lasting for seconds or minutes, usually
affecting one eye only and caused by

ALVEOLUS, PULMONARY
Trachea

Thin wall
of alveolus
Air space

Pleura

Blood
vessel

ALVEOLI
Bronchus

LUNGS

Bronchiole

Alzheimer’s disease A progressive condition in which nerve cells in the brain
degenerate and the brain shrinks. Alzheimer’s disease is the most common
cause of dementia. Onset is uncommon
before the age of 60.
Early onset Alzheimer's disease, in
which symptoms develop before age 60,
is inherited as a dominant disorder. Late
onset Alzheimer's disease is associated
with a number of genes, including 3 that
24

AMBIDEXTERITY

AMFETAMINE DRUGS

the temporary blockage of a small
blood vessel in the eye by emboli (particles of solid matter such as cholesterol
or clotted blood). These are carried in
the bloodstream from diseased arteries
in the neck or, rarely, the heart. Attacks
may be infrequent or they may occur
many times a day. This symptom indicates an increased risk of stroke and
requires medical investigation.
ambidexterity The ability to perform
manual skills equally well with either
hand because there is no definite handedness. Ambidexterity is an uncommon
and often familial trait.
amblyopia A permanent defect of visual acuity in which there is usually no
structural abnormality in the eye. In
many cases, there is a disturbance of
the visual pathway between the retina
and the brain. The term is also sometimes applied to toxic or nutritional
causes of decreased visual acuity, as in
tobacco–alcohol amblyopia.
Amblyopia will develop if there is a
marked discrepancy between the images
received by the brain from each eye
while vision is developing during early
childhood. The most common cause is
squint. Failure to form normal retinal
images may also result from congenital
cataract, and severe, or unequal, focusing errors, such as when one eye is
normal and there is an uncorrected
large degree of astigmatism in the other.
Toxic and nutritional amblyopia may
result from damage to the retina and/or
the optic nerve.
To prevent amblyopia due to squint,
patching (covering up the good eye to
force the deviating eye to function properly) is the usual treatment. Surgery to
place the deviating eye in the correct
position may be necessary. Glasses may
be needed to correct severe focusing
errors. Cataracts may be removed surgically. After the age of 8, amblyopia
cannot usually be remedied.
ambulance A vehicle for transporting
sick or injured people that is staffed by
trained personnel who can provide emergency treatment during the journey.
ambulatory ECG In ambulatory ECG
(electrocardiography), a wearable device
called a Holter monitor is used to record

the electrical activity of the heart by
means of electrodes attached to the
chest. The monitor is usually worn for
24 hours or longer and detects intermittent arrhythmias (abnormal heart rates
and rhythms). The wearer can press a
button on the monitor to mark the
recording whenever symptoms occur.
The recording can later be analysed
to see if the periods of arrhythmia
coincide with the symptoms.
amelogenesis imperfecta An inherited
condition of the teeth in which the
enamel is either abnormally thin or is
deficient in calcium. Affected teeth may
be pitted and discoloured (see discoloured teeth) and more susceptible to
dental caries (tooth decay) and wear.
amenorrhoea The absence of menstrual periods. Primary amenorrhoea is
defined as failure to start menstruating
by the age of 16. Secondary amenorrhoea is the temporary or permanent
cessation of periods in a woman who
has menstruated regularly in the past.
The main cause of primary amenorrhoea is delayed puberty. The delay may
not indicate a disorder, but, rarely, it may
result from a disorder of the endocrine
system, such as a pituitary tumour,
hypothyroidism, an adrenal tumour, or
adrenal hyperplasia. Another rare cause
of delayed puberty is Turner’s syndrome.
In some cases, menstruation fails to
take place because the vagina or the
uterus has been absent from birth, or
because there is no perforation in the
hymen to allow blood to escape.
The most common cause of temporary
secondary amenorrhoea is pregnancy.
Periods may also cease temporarily after
a woman has stopped taking oral contraceptives. Secondary amenorrhoea may
also result from hormonal changes due
to stress, depression, anorexia nervosa,
or certain drugs. Another possible
cause is a disorder of the ovary such as
polycystic ovary (see ovary, polycystic)
or an ovarian tumour. Amenorrhoea
occurs permanently following the menopause or after a hysterectomy.
amfetamine drugs A group of stimulant drugs used mainly in the treatment
of narcolepsy (a rare disorder characterized by excessive sleepiness).
25

A

A

AMILORIDE

AMNIOCENTESIS

amiodarone An antiarrhythmic drug used
in the treatment of various types of
arrhythmia (irregular heartbeat). Longterm use of amiodarone may result in
inflammation of the liver, thyroid problems, and eye and lung damage.
amitriptyline A tricyclic antidepressant
drug with a sedative effect. It is useful
in the treatment of depression accompanied by anxiety or insomnia. Possible
adverse effects include blurred vision,
dizziness, and drowsiness.
amlodipine A calcium channel blocker
drug used to prevent angina and to treat
hypertension. Possible side effects are
headaches and dizziness.
ammonia A colourless, pungent gas that
dissolves in water to form ammonium
hydroxide, an alkaline solution (see alkali). Ammonia is produced in the body
and helps to maintain the acid–base balance. In severe liver damage, the ability
of the liver to convert ammonia to urea
is reduced. This leads to a high level of
ammonia in the blood, which is thought
to be a cause of the impaired consciousness that occurs in liver failure.
amnesia Loss of ability to memorize
information and/or to recall information
stored in memory. Possible causes of
amnesia are head injury; degenerative
disorders such as Alzheimer’s disease
and other forms of dementia; infections
such as encephalitis; thiamine deficiency in alcoholics, leading to Wernicke–
Korsakoff syndrome; brain tumours;
strokes; and subarachnoid haemorrhage.
Amnesia can also occur in some forms
of psychiatric illness.
In retrograde amnesia, the loss of
memory extends back for some time
before the onset of the disorder. In
anterograde amnesia, there is an inability to store new information in the
period following the onset of illness.
amniocentesis A diagnostic procedure
in which a small amount of amniotic
fluid is withdrawn, using a syringe and
guided by ultrasound scanning, from
the amniotic sac that surrounds the
fetus in the uterus. This fluid contains
fetal cells that can be subjected to
chromosome analysis to identify chromosomal defects such as Down’s syndrome
or genetic analysis to look for genetic

In high doses, amfetamines can cause
tremor, sweating, anxiety, and sleeping
problems. Delusions, hallucinations, high
blood pressure, and seizures may also
occur. Prolonged use may produce tolerance and drug dependence.
Amfetamines are often abused for
their stimulant effect.
amiloride A potassium-sparing diuretic
drug. Combined with loop or thiazide
diuretics, amiloride is used to treat
hypertension and fluid retention due to
heart failure or cirrhosis of the liver.
amino acids A group of chemical compounds that form the basic structural
units of all proteins. Each amino acid
molecule consists of amino and carboxyl
groups of atoms linked to a variable
chain or ring of carbon atoms.
Individual amino acid molecules are
linked together by chemical bonds
called peptide bonds to form short
chains of molecules called polypeptides.
Hundreds of polypeptides are, in turn,
linked together, also by peptide bonds,
to form a protein molecule. What differentiates one protein from another is the
sequence of the amino acids.
There are 20 different amino acids that
make up all the proteins in the body. Of
these, 12 can be made by the body; they
are known as nonessential amino acids
because they do not need to be obtained from the diet. The other 8, known
as the essential amino acids, cannot be
made by the body and must therefore
be obtained from the diet.
aminoglutethimide An anticancer drug
used to treat certain types of breast
cancer, prostate cancer, and some endocrine gland tumours.
aminoglycoside drugs A type of antibiotic drug. Aminoglycoside drugs are
given by injection and are generally
reserved for the treatment of serious
infections because their use can damage the inner ear or kidneys. Important
examples are gentamicin and streptomycin, which are also used topically for
eye and ear infections.
aminophylline A bronchodilator drug
used to treat chronic bronchitis, asthma,
and, occasionally, heart failure. Nausea,
vomiting, headache, dizziness, and palpitations are possible side effects.
26

AMNION

AMOXICILLIN

Occasionally, excessive fluid is formed
(see polyhydramnios); less frequently,
insufficient amniotic fluid is formed
(see oligohydramnios).
amniotic sac The membranous bag that
surrounds the fetus and is filled with
amniotic fluid as pregnancy advances.
The sac is made up of 2 membranes, the
inner amnion and the outer chorion.
amniotomy Artificial rupture of the amniotic membranes (breaking the “waters”)
performed for induction of labour.
amoeba A type of protozoon (see protozoa). An amoeba is a microscopic
single-celled organism with an irregular,
changeable shape. Amoebae live in
moist environments, such as fresh
water and soil. Some types of amoebae
are parasites of humans, causing diseases such as amoebiasis.
amoebiasis An infection caused by the
amoeba ENTAMOEBA HISTOLYTICA, a tiny
single-celled parasite that lives in the
human large intestine. Amoebiasis is
spread through drinking water or eating
food contaminated by human excreta
containing cysts of the amoeba.
Some people carry the amoeba in their
intestines and excrete cysts but have no
symptoms. However, some strains invade and ulcerate the intestinal wall,
causing diarrhoea and abdominal pain,
which may develop into full-blown
dysentery. The amoebae may spread via
the bloodstream to the liver, or, rarely,
the brain or lung, where they cause
abscesses. Symptoms of an amoebic
liver abscess are chills, fever, weight
loss, and painful enlargement of the liver.
Treatment of all forms of amoebiasis
is with drugs such as metronidazole or
diloxanide, which kill the parasite within a few weeks, leading to full recovery.
amoebic dysentery See amoebiasis.
amoebicides A group of drugs used to
treat amoebiasis. Examples are diloxanide, and metronidazole.
amoxapine An antidepressant drug related to the tricyclics. Possible adverse
effects include blurred vision, dizziness,
drowsiness, abnormal muscular movements, menstrual irregularities, and
breast enlargement.
amoxicillin A penicillin drug commonly
used to treat a variety of infections,

AMNIOCENTESIS
Syringe

Ultrasound
probe

Amniotic
fluid

Ultrasound
beam

Bladder
Fetus

Cervix
Uterus

Placenta

disorders such as haemophilia, cystic
fibrosis, and Tay–Sachs disease. Chemi-

cal analysis of amniotic fluid can help
to diagnose developmental abnormalities such as spina bifida. Rhesus
incompatibility and maturity of the fetal
lungs can also be checked.
Amniocentesis is usually performed in
the 14th–18th week of pregnancy. It
slightly increases the risk of miscarriage
or early rupture of the membranes and is
therefore recommended only when the
fetus is thought to be at increased risk
of an abnormality. (See also antenatal
care, chorionic villus sampling.)
amnion One of the membranes that
surrounds the fetus in the uterus. The
outside of the amnion is covered by
another membrane called the chorion.
amniotic fluid The clear, watery fluid
(popularly called the “waters”) that surrounds the fetus in the uterus. The fluid
is contained within the amniotic sac. It
cushions the fetus, allowing movement.
Amniotic fluid is produced by cells lining the amniotic sac and is constantly
circulated. It appears in the 1st week
after conception and gradually increases in volume until the 10th week,
when the increase becomes very rapid.
27

A

A

AMOXYCILLIN

AMYLOIDOSIS

including bronchitis, cystitis, and ear and
skin infections. Allergy to amoxicillin
causes a blotchy rash and, rarely, fever,
swelling of the mouth and tongue, itching, and breathing difficulty.
amoxycillin See amoxicillin.
amphetamine drugs See amfetamine
drugs.
amphotericin B A drug used to treat
fungal infections. Lozenges are used for
candidiasis of the mouth. Life-threatening infections, such as cryptococcosis
and histoplasmosis, are treated by injection. Adverse effects may occur with
injection and include vomiting, fever,
headache, and, rarely, seizures.
ampicillin A penicillin drug commonly
used to treat cystitis, bronchitis, and ear
infections. Diarrhoea is a common
adverse effect of ampicillin. Some people are allergic to it and suffer from
rash, fever, swelling of the mouth and
tongue, itching, and breathing difficulty.
ampulla An enlarged, flask-shaped area
at the end of a tubular structure or
canal. There are several ampullae in the
body, including at the end of the fallopian tubes, at the opening of the bile
duct into the intestine, and on each of
the semicircular canals of the inner ear.

development of gangrene. Amputation
may also be needed if a limb has been
irreparably damaged in an accident.
For some time after amputation, there
may be an unpleasant sensation that the
limb is still present, a phenomenon
known as “phantom limb”. A prosthesis
(see limb, artificial) is usually fitted
when the stump has healed.
amputation, congenital The separation of a body part (usually a limb,
finger, or toe) from the rest of the body,
as a result of the part’s blood supply
being blocked by a band of amnion
(fetal membrane) in the uterus. The
affected part may be completely separated or show the marks of the “amniotic
band” after birth. (See also limb defects.)
amputation, traumatic Loss of a finger, toe, or limb through injury. (See
also microsurgery.)
amylase An enzyme found in saliva and
pancreatic secretions (see pancreas). It
helps to digest dietary starch, breaking
it down into smaller components such
as the sugars glucose and maltose.
amyl nitrite A nitrate drug formerly prescribed to relieve angina. Because amyl
nitrite frequently causes adverse effects,
it has been superseded by other drugs. It
is sometimes abused for its effect of
intensifying pleasure during orgasm.
amyloidosis An uncommon disease in
which a substance called amyloid, composed of fibrous protein, accumulates
in tissues and organs, including the
liver, kidneys, tongue, spleen, and heart.
Amyloidosis may occur for no known
reason, in which case it is called primary;
more commonly, it is a complication of
some other disease, and in such cases
it is called secondary. Conditions that
may lead to amyloidosis include multiple myeloma (a cancer of bone marrow),
rheumatoid arthritis, tuberculosis, and
some other longstanding infections,
such as chronic osteomyelitis.
The symptoms of amyloidosis vary,
depending on the organs affected and
the duration of the condition. Deposits
of amyloid in the kidneys may cause
kidney failure, which may be fatal.
There is no treatment, but secondary
amyloidosis can be halted if the underlying disorder is treated.

AMPULLA
Semicircular canal

Cochlea

Ampulla
Outer Middle Inner
ear
ear
ear

INNER EAR
Cochlea

LOCATION

amputation Surgical removal of part or
all of a limb. Amputation is necessary if
peripheral vascular disease as a result of
atherosclerosis or diabetes mellitus has
impaired the blood supply to a limb. If
blood supply cannot be restored, amputation is carried out to prevent the
28

AMYOTROPHIC LATERAL SCLEROSIS

ANAEMIA, HAEMOLYTIC

amyotrophic lateral sclerosis See
motor neuron disease.
amyotrophy Shrinkage or wasting away
of a muscle, leading to weakness. Amyotrophy is usually due to poor nutrition,
reduced use of the muscle (as when a
limb is immobilized for a long period),
or disruption of the blood or nerve supply to the muscle (as can occur in
diabetes mellitus or poliomyelitis).
anabolic steroids See steroids, anabolic.
anabolism The manufacture of complex
molecules, such as fats and proteins,
from simpler molecules by metabolic
processes in living cells. (See also
catabolism; metabolism.)
anaemia A condition in which the concentration of the oxygen-carrying pigment
haemoglobin in the blood is below normal. Haemoglobin molecules are carried
inside red blood cells and transport
oxygen from the lungs to the tissues.
Normally, stable haemoglobin concentrations in the blood are maintained by
a balance between red-cell production
in the bone marrow and red-cell destruction in the spleen. Anaemia may
result if this balance is upset.
Anaemia is not a disease but a feature
of many different disorders. There are
various types, which can be classified
into those due to decreased or defective
red-cell production by bone marrow (see
anaemia, aplastic; anaemia, megaloblastic;
anaemia, iron-deficiency) and those due
to decreased survival of the red cells in
the blood (see anaemia, haemolytic).
The severity of symptoms depends on
how low the haemoglobin concentration has become. Slightly reduced
levels can cause headaches, tiredness,
and lethargy. Severely reduced levels
can cause breathing difficulty on exercise, dizziness, angina, and palpitations.
General signs include pallor, particularly of the skin creases, the lining of the
mouth, and the inside of the eyelids.
Anaemia is diagnosed from the symptoms and by blood tests (see blood
count; blood film). A bone marrow biopsy may be needed if the problem is with
red blood cell production.
anaemia, aplastic A rare but serious
type of anaemia in which the red cells,
white cells, and platelets in the blood

are all reduced in number. Aplastic
anaemia is caused by a failure of the
bone marrow to produce stem cells, the
initial form of all blood cells.
Treatment of cancer with radiotherapy
or anticancer drugs can temporarily
interfere with the cell-producing ability
of bone marrow, as can certain viral
infections and other drugs. Long-term
exposure to insecticides or benzene
fumes may cause more persistent aplastic anaemia, and a moderate to high
dose of nuclear radiation is another
recognized cause. An autoimmune disorder is responsible in about half of
all cases. Aplastic anaemia sometimes
develops for no known reason.
A low level of red blood cells may
cause symptoms common to all types
of anaemia, such as fatigue and breathlessness. White-cell deficiency increases
susceptibility to infections; platelet deficiency may lead to a tendency to bruise
easily, bleeding gums, and nosebleeds.
The disorder is usually suspected from
blood-test results, particularly a blood
count, and is confirmed by a bone marrow
biopsy. Blood and platelet transfusions
can control symptoms. Immunosuppression is used to treat anaemia due to an
autoimmune process. Severe persistent
aplastic anaemia may be fatal unless a
bone marrow transplant is carried out.
anaemia, haemolytic A form of anaemia
caused by premature destruction of red
cells in the bloodstream (haemolysis).
Haemolytic anaemias can be classified
according to whether the cause of haemolysis is inside or outside the red cells.
When haemolysis is due to a defect
inside the red cells, the underlying
problem is abnormal rigidity of the cell
membrane. This causes the cells to
become trapped, at an early stage of
their life-span, in the small blood vessels
of the spleen, where they are destroyed
by macrophages (cells that ingest foreign particles). Abnormal rigidity may
result from an inherited defect of the
cell membrane (as in hereditary spherocytosis), a defect of the haem