Bma Illustrated Medical Dictionary

azelaic acidA topicaldrug used to treat

mild to moderate acne.

azithromycinA macrolide antibiotic

drugused to treat infections of the skin,

chest, throat, and ears. Azithromycin is

also used to treat genital infections due

to chlamydia (see chlamydial infections).

azoospermiaThe absence of sperm from

semen, causing infertilityin males. Azoo-

spermia may be caused by a disorder

present at birth or that develops later in

life or after vasectomy.

Congenital azoospermia may be due

to a chromosomal abnormalitysuch as

Klinefelter’s syndrome; failure of the

testes to descend into the scrotum;

absence of the vasa deferentia (ducts

that carry sperm from the testes to the

seminal vesicles); or cystic fibrosis.

In some males, azoospermia may be

the result of hormonal disorders affect-

ing the onset of puberty. Another cause

is blockage of the vasa deferentia,

which may follow a sexually transmitted

infection, tuberculosis, or surgery on the

groin. Azoospermia can also be the re-

sult of damage to the testes. This can

follow radiotherapy, treatment with cer-

tain drugs, and prolonged exposure to

heat, or the effects of occupational

exposure to toxic chemicals.

If the cause is treatable, sperm pro-

duction may restart. However, in some

cases, the testes will have been perma-

nently damaged.

AZTThe abbreviation for azidothymi-

dine, the former name for zidovudine.

aztreonamAn antibioticused to treat

some types of meningitisand infections

by certain types of bacteria, including

PSEUDOMONAS.

AVERSION THERAPY AZTREONAM

A aversion therapyAn outdated form of
behaviour therapyin which unpleasant
stimuli, such as electric shocks, are
administered at the same time as an
unwanted behaviour in an attempt to
alter behavioural patterns.
aviation medicineThe medical spe-
ciality concerned with the physiological
effects of air travel and with the causes
and treatment of medical problems that
may occur during a flight.
avulsed toothA tooth that has become
completely dislodged from its socket
following an injury. If the tooth is kept
moist, and treatment is sought immedi-
ately, reimplantation may be possible
(see reimplantation,dental).
avulsionThe tearing away of a body
structure from its point of attachment.
For example, excessive contraction of a
tendonmay avulse a small piece of
bone at its attachment point. Avulsion
may be due to an injury or be per-
formed as part of a surgical procedure.
axillaThe medical name for the armpit.
axisThe 2nd cervical vertebrain the
human spine. The axis is attached by a
pivot joint to the atlas, the topmost ver-
tebra, which in turn is attached to the
base of the skull. The pivot joint allows
the head to turn to either side.
axonThe thin, elongated part of a neu-
ron (nerve cell) that conducts nerve
impulses. Many axons in the body are
covered with a fatty myelinsheath.

AyurvedismSeeIndian medicine.

azathioprineAn immunosuppressant drug

used to treat severe rheumatoid arthritis

and other autoimmune disorders. It is

also used to prevent organ rejection

after transplant surgery. Increased sus-

ceptibility to infection is a side effect.

Axon

(nerve fibre)

Myelin

sheath

Nerve cell body

AXON

Nucleus

Nerve-cell

ending

NERVE CELL