The adrenal gland has two
distinct endocrine components: the cortex and the medulla
The adrenal cortex synthesizes, stores and secretes three main groups of
hormone, all of which are steroid hormones synthesized from cholesterol:
• Glucocorticoid hormones, e.g. hydrocortisone from zona fasciculata.
• Mineralocorticoid hormone (aldosterone), from the zona glomerulosa.
• Sex steroids, from zona reticularis.
The adrenal medulla is derived
embryologically from neural crest ectoderm and is part of the sympathetic
It synthesizes and secretes the vasoactive amines, adrenaline and noradrenaline
(epinephrine and norepinephrine).
Excessive production of adrenal cortical hormones usually results from
hyperplasia or a tumour.
Excessive ACTH production, for example by an ACTH-secreting adenoma of the
pituitary, stimulates an increase in the number, size and secretory activity of
the adrenal cortical cells, leading to adrenal cortical hyperplasia.
The uncontrolled excessive production of adrenal cortical hormones may produce
Adrenal cortical adenoma is a
well-circumscribed, yellow tumour in the adrenal cortex, which is usually 2-5 cm
The colour of the tumour, as with the adrenal cortex as a whole, is due to the
stored lipid (mainly cholesterol), from which the cortical hormones are
These tumours are frequent incidental findings at post mortem examination, and
appear to have produced no significant metabolic disorder; only a very small
percentage produce Cushing's syndrome.
Nevertheless, these apparently 'non-functioning' adenomata are most often
encountered in elderly obese people.
There is some debate that they may really represent nodules in diffuse nodular
Very occasionally, a true adrenal cortical adenoma is associated with the
clinical manifestations of Conn's syndrome, and can be shown to be excreting
Adrenal cortical carcinoma is
rare, and virtually every case is associated with excessive production of
hormones, usually gluco-corticoids and sex steroids.
As a result the patients usually have features of Cushing's syndrome mixed with
androgenic effects, which are particularly noticeable in women.
The tumours are usually large and yellowish white, and local invasion and
metastatic spread are common.
Ectopic ACTH secretion may be
associated with non-adrenal tumours, particularly oat-cell carcinoma of the
bronchus and some carcinoid tumours.
In cases of the highly malignant bronchial tumour the symptoms are mainly
metabolic, with hypokalaemia, alkalosis and impaired glucose tolerance.
The patient rarely survives long enough to develop the physical features of
Cushing's syndrome, although these and hypertension may develop if the
inappropriate secretion is due to a less rapidly fatal tumour.
Chronic adrenal cortical
insufficiency produces Addison's disease
Addison's disease is caused by
chronic adrenal cortical insufficiency due to lack of glucocorticoids and
The main features of the disease are: low serum sodium and high serum potassium,
with chronic dehydration; hypotension, often markedly postural; lethargy and
weakness; vomiting and loss of appetite; and brownish pigmentation of skin and
The most common cause is
destruction of the cortex of both adrenals by autoimmune adrenalitis often
associated with autoimmune thyroid disease and autoimmune gastritis and other
endocrine organ autoimmune disease.
Other causes are bilateral adrenal tuberculosis, fungal infections and adrenal
destruction by tumour, but all are rare.
The adrenal is reduced in size
and there is a heavy lymphocytic infiltrate, a manifestation of autoimmune
ACUTE ADRENAL CORTICAL
Acute adrenal cortical failure
is usually due to haemorrhagic infarction, but may be iatrogenic
necrosis of the adrenals is usually associated with disseminated intravascular
It is a feature of severe septicaemia, particularly meningococcal septicaemia,
in which it is known as the 'Waterhouse-Friderichsen syndrome'.
There is hypovolaemic and hypotensive shock, with hypoglycaemia, and high risk
of sudden death.
Iatrogenic acute adrenal
cortical failure may occur when prolonged high-dose therapeutic corticosteroid
therapy is abruptly stopped.
Prolonged corticosteroid therapy leads to suppression of normal endogenous
steroid production by the adrenal cortex, which becomes markedly atrophied.
Cessation of exogenous steroid therapy produces acute adrenal cortical failure
(adrenal crisis), with hypovolaemic and hypotensive shock, hypoglycaemia, and
risk of sudden death.