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.
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.
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.
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.
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.
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
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.
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
Remember the hormones each zone of the cortex secretes:
G: salt (mineralocorticoids)
F: sugar (corticosteroids)
R: sex (androgens)
The adrenal glands are paired suprarenal structures with a dual embryological origin. They are responsible for the secretion of vital hormones.