Overview
The adrenal glands are paired retroperitoneal structures, and are also
known as the suprarenal glands. They are
responsible for the secretion of numerous steroids and catecholamines.
Gross Anatomy
Development
The adrenal
glands begin to develop at 6 weeks gestation.
The adrenal gland is composed of a cortex and medulla and these have
different embryological origins. The
cortex is derived from mesothelium while the inner medulla originates from
neural crest cells along with the sympathetic nervous system. The adrenal foetal cortex is particularly
well developed in utero and at 4 months gestation, the adrenal glands far
outsize the kidney due to the cortex proliferation. The glands secrete hormones in utero that aid
lung maturation. After birth, the foetal
cortex is gradually replaced by adult adrenal cortex.
Surface Anatomy
The
adrenals lie in the lateral retroperitoneum, superomedial to the kidneys. The right adrenal gland normally sits higher
than the left, to the liver displacing it inferiorly.
Macro-Anatomy (e.g. lobes, surfaces,
impressions etc)
The adrenal
glands are surrounded by renal fascia which attaches them to the crura of the
diaphragm. Both the right and left glands lie on top of the superior pole of
the kidneys. Although paired, the adrenal glands are different in shape. The right adrenal gland is pyramidal and has
the Internal vena cava (IVC) with the diaphragm posteriorly. The left adrenal gland is more crescent
shaped and closely related to the spleen, stomach, pancreas and left crus of
the diaphragm.
Micro-Anatomy
Each
adrenal gland has an outer cortex and inner medulla. The cortex is further divided into 3 separate
zones which are responsible for the production and secretion of cholesterol
derived hormones:
Zona
glomerulosa: mineralocorticoids e.g aldosterone
Zona fasciculata:
corticosteroids e.g. cortisol
Zona
reticularis: androgens e.g. dehydroepiandrosterone
The medulla
is located in the centre of each gland. Chromaffin
cells secrete adrenaline and noradrenaline, which are involved in the
sympathetic nervous system response.
Blood Supply
The adrenal
glands have a rich blood supply. They
are each supplied by 3 suprarenal arteries:
Superior
suprarenal: normally six to eight, originates from the inferior phrenic artery.
Middle
suprarenal: one or more, originates from the abdominal aorta, near to the
superior mesenteric root.
Inferior
suprarenal: one or more, directly from the renal artery.
The venous
drainage is via a single suprarenal vein.
The right suprarenal vein drains directly into the IVC, while the left
takes joins the left renal vein, which then drains into the inferior vena cava.
Lymph
Lymphatic
drainage goes to the lumbar lymph nodes.
Nerve Supply (link to dermatome and
referred pain as appropriate)
The coeliac
plexus and abdominopelvic splanchnic nerves provide innervation to the adrenal
glands. The adrenal medulla receives sympathetic
innervation via myelinated presynaptic fibres, originating in the lateral horn
of the spinal cord, largely T10-L1.
Physiology (e.g. functions,
relationships to other body systems)
The adrenal
glands are responsible for corticosteroid and androgen release from the adrenal
cortex, and adrenaline and noradrenaline from the medulla. Corticosteroid
release from the adrenal glands are involved in the stress response, and also
have a role in carbohydrate and protein metabolism, as well as having an anti-inflammatory
role.
The
catecholamines (adrenaline and noradrenaline) are involved in the sympathetic
response of the body i.e. fight, fright and flight responses
Clinical Anatomy
Phaeochromocytoma:
This is a rare neuroendocrine tumour that develops from the
chromaffin cells of the adrenal medulla.
Patients can present with hypertension resistant to medication and other
signs of hyperstimulation of the sympathetic nervous system due to the tumour
secreting catecholamines. These include
a heightened sense of anxiety, a sense of impending doom, and tachycardia. It
is associated with Multiple endocrine neoplasia (MEN) 2a and 2b, two inherited
cancer causing syndromes. Urinary or
blood catecholamines are elevated and CT imaging may show an adrenal lesion.
80% are unilateral and definitive treatment
is alpha blockade and beta blockade (in that order), followed by surgical
removal.
Conn’s
Syndrome: is also known as primary hyperaldosteronism. Two thirds are caused by adrenal hyperplasia and
the remaining one third by an adrenal adenoma.
Investigations include blood aldosterone-renin ratio and a low serum
potassium is classically described.
Patients are often asymptomatic but may experience muscle weakness,
tingling and hypertension. Treatment for
a solitary adenoma is adrenalectomy, for adrenal hyperplasia drug treatment
includes spironolactone and aldosterone antagonists.
Quick Anatomy
Key Facts
Development:
cortex- mesothelium, medulla- neural crest
Artery: superior,
middle and inferior suprarenal arteries.
Vein: single
suprarenal vein
Lymph: lumbar
nodes
Nerve: coeliac
and abdominopelvic splanchnic nerves
Aide-Memoire
Remember the hormones each zone of the cortex secretes:
G: salt
(mineralocorticoids)
F: sugar
(corticosteroids)
R: sex
(androgens)
Summary
The adrenal glands are paired suprarenal structures with a dual
embryological origin. They are
responsible for the secretion of vital hormones.