ANDROGEN HORMONES
ANEURYSM
A
androgen hormones
A group of hor-
mones that stimulate the development
of male sexual characteristics.
Androgens are produced by special-
ized cells in the testes in males and in
the adrenal glands in both sexes. The
ovaries secrete very small quantities of
androgens until the menopause. The
most active androgen is
testosterone,
which is produced in the testes. The
production of androgens by the testes
is controlled by certain pituitary hor-
mones, called
gonadotrophins
. Adrenal
androgens are controlled by
ACTH
,
another pituitary hormone.
Androgens stimulate male secondary
sexual characteristics at
puberty
, such
as the growth of facial hair and deepen-
ing of the voice. They have an anabolic
effect (they raise the rate of protein syn-
thesis and lower the rate at which it is
broken down). This increases muscle
bulk and accelerates growth. At the end
of puberty, androgens cause the long
bones to stop growing. They stimulate
sebum secretion, which, if excessive,
causes
acne.
In early adult life, andro-
gens promote male-pattern baldness.
Androgen deficiency may occur if the
testes are diseased or if the pituitary
gland fails to secrete gonadotrophins.
Typical effects include decreased body
and facial hair, a high-pitched voice,
underdevelopment of the genitalia, and
poor muscle development.
Overproduction of androgens may be
the result of adrenal disorders (see
adrenal tumours; adrenal hyperplasia,
congenital),
of testicular tumours (see
testis
,
cancer of
), or, rarely, of androgen-
secreting ovarian tumours (see
ovary
,
cancer of
). In men, excess androgens
accentuate male characteristics; in boys,
they cause premature sexual develop-
ment. In women, excess androgens cause
virilization,
the development of mascu-
line features such as an increase in
body hair, deepening of the voice, cli-
toral enlargement, and
amenorrhoea.
anencephaly
Absence of the brain and
cranial vault (top of the skull) at birth.
Most infants with anencephaly are still-
born or survive only a few hours.
Anencephaly is detectable early in preg-
nancy by measurement of the maternal
alpha-fetoprotein,
by
ultrasound scan-
ning
, by
amniocentesis
, or by
fetoscopy
;
if anencephaly is detected, termination
of the pregnancy may be considered.
Anencephaly is due to a failure in the
development of the neural tube, which
is the nerve tissue in the embryo that
normally develops into the spinal cord
and brain. (See also
neural tube defects.)
aneurysm
Abnormal dilation (balloon-
ing) of an
artery
caused by the pressure
of blood flowing through a weakened
area. Aneurysms most commonly affect
the
aorta
and arteries supplying the brain.
The most common cause of an aneu-
rysm is
atherosclerosis
, a condition in
which fatty deposits weaken the artery
wall. The aorta is the usual site of
atherosclerotic aneurysms.
Less commonly, aneurysms may be
due to a congenital weakness of the
artery walls. Most cerebral aneurysms,
known as berry aneurysms because of
their appearance, are congenital.
Mar-
fan's syndrome,
an inherited disorder in
which the muscular layer of the aorta
is defective, is often associated with
aneurysms just above the heart. The
arterial wall can
also be weakened
ANEURYSM
by inflammation,
Weakened, bulging
as occurs in
poly-
arteritis nodosa
.
Most aneurysms
are symptomless
and remain un-
detected,
but if
the aneurysm ex-
pands rapidly and
causes pain, or it
is very large, the
symptoms are due
to
pressure
on
Fatty
nearby structures.
deposit
Aneurysms may
eventually rupture, cause fatal blood
loss, or, in the case of a cerebral
aneurysm, loss of consciousness (see
subarachnoid haem orrhage
).
In some cases, only the inner layer of
the artery wall ruptures, which allows
blood to track along the length of the
artery and block any branching arteries.
There is usually severe pain and high
risk of rupture occurring.
34
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