The rate at which many glands produce hormones is influenced by other hormones,
especially those secreted by the pituitary gland and the hypothalamus. Ifthe
amount of hormone produced is increased, negative feedback mechanisms act
on the hypothalamus and pituitary so that they produce less of their stimulating
hormones, thus reducing the target gland’s activity. Ifthe amount of hormone
produced is decreased, the feedback weakens, causing increased production of
Stimulated bya releasing
factorsecreted by the
hypothalamus, the anterior
Released into the
pituitary, ACTH acts
directlyon the cortex
of the adrenal glands.
Stimulated bythe ACTH,
the adrenal cortex
and other corticosteroid
Influences the pituitaryby
secreting hormones called
releasing factors. The
hypothalamus itself is
coming from manyparts
of the body.
. Negative feedback
If the level of
hydrocortisone in the
blood rises, it has a
effect inhibiting ACTH
pituitary. This has
the effect of slowing
response to stimulation by sympathetic
nerves. These nerves are most active
during times of stress.
The release of these hormones into
the circulation produces effects similar
to sympathetic nerve stimulation. The
heart rate and force of contraction of
the heart muscle increase so that more
blood is pumped around the body and
the airways are widened to ease breath-
vessels in the intestines, kidneys, and
liver, and widen blood vessels supplying
more blood is supplied to the active
muscles and less to the internal organs.
adrenal hyperplasia, congenital
birth, in which an
that acts as a catalyst) defect blocks the
production of corticosteroid hormones
the adrenal glands.
The enzyme block results in production
(male sex hormones), which can cause
abnormal genital development in an
affected fetus. In females, these andro-
gens cause enlargement of the clitoris
and some fusion of the outer lips of the
vulva, resulting in genital ambiguity
males have an enlarged penis, which
may either be evident at birth or may
Other effects of the enzyme defect
(low blood pres-
(low blood sugar
levels), weight loss, and dehydration.
(enlargement) of the adre-
secretion of the hormone
is a result of insufficient production of
hydrocortisone. Excessive skin pigmen-
tation may occur in skin creases and
around the nipples.
In severe cases, congenital adrenal
hyperplasia is apparent soon after birth.
In milder cases, symptoms appear later,
sometimes producing premature puber-
ty in boys and delayed menstruation,
(excessive hairiness), and po-
tential infertility in girls.
DIAGNOSIS AND TREATMENT
A diagnosis is confirmed by measuring
corticosteroid hormones in the blood
carried out to verify that there is no
tumour of the adrenal glands.
Treatment of congenital adrenal hyp-
erplasia is with hormone replacement.
If the treatment is started early, normal
sexual development and fertility gener-
Also called epinephrine, a hormone re-
leased by the adrenal glands in response
to signals from the sympathetic nervous
system, part of the
These signals are triggered by
stress, exercise, or emotions such as fear.
Adrenaline increases the speed and
force of the heartbeat. It widens the air-
ways 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 giv-
en by injection as emergency treatment
(a severe allergic
(a halt in the
heart’s pumping action). Eye-drops con-
taining dipivefrine (a drug that passes
quickly into the tissues and converts to
adrenaline), may be used to treat acute
Regular use can
cause a burning pain and, occasionally,
blurred vision or pigment deposits on
the eye surface. (See also
Rare cancerous or noncancerous tum-
causing excess secretion of hormones.
Tumours of the adrenal cortex may
(also called Conn’s syn-
Tumours of the adrenal medulla may
cause excessive secretion of
inephrine). Two types of tumour affect
which affects children.
These tumours may cause intermittent
(high blood pressure) and
Surgical removal of a tumour or an
adrenal gland usually cures noncancer-
ous tumours. Cancerous tumours may
require additional treatment with