A cap of tissue on the upper pole of each kidney, named for its position beside that organ
Adrenal gland — also called the suprarenal gland.
Anatomy · Glands & the immune system
Adrenal gland
One on top of each kidney
Endocrine system · upper pole of the kidney
Two small glands, one perched on the upper pole of each kidney, embedded in fat behind the peritoneum. Each has an outer cortex, which makes steroid hormones such as cortisol and aldosterone, and an inner medulla, which makes adrenaline and noradrenaline. The right gland is roughly pyramidal and the left crescent-shaped. Together they manage salt and water balance, blood sugar, the response to stress and the 'fight or flight' reaction.
How to spot them
- ▸A small yellowish cap sitting on the top of each kidney, inside the renal fascia
- ▸Right gland triangular or pyramidal; left gland crescent-shaped
- ▸In section, a yellow cortex around a darker, reddish-brown medulla
- ▸The cortex has three layers: a thin outer zona glomerulosa, a thick zona fasciculata and an inner zona reticularis
- ▸The right gland drains directly into the inferior vena cava; the left drains to the left renal vein
What to know
A cortex in three layers, sometimes recalled as 'salt, sugar and sex' from outside in
Adrenal gland — glomerulosa (aldosterone), fasciculata (cortisol), reticularis (androgens).
A core of modified nerve cells that release adrenaline into the blood when the sympathetic system fires
Adrenal gland — the medulla, made of chromaffin cells.
Failure of its cortex was described in 1855 by a physician at Guy's Hospital, with bronzed skin and weakness (1855)
Adrenal gland — Thomas Addison, hence Addison's disease.
The zone of the cortex that makes cortisol, in the thick middle layer, under orders from ACTH
Adrenal gland — the zona fasciculata, a layer of its cortex.
The right one's short vein empties straight into the great vein of the abdomen, the left one's into a kidney vein
Adrenal gland — right into the IVC, left into the left renal vein.
In 1901 the Japanese chemist Jōkichi Takamine isolated the hormone from this organ's core (1901)
Adrenal gland — adrenaline (epinephrine), among the first hormones obtained in pure form (Thomas Aldrich isolated it independently).
Key ideas
- The cortex is controlled by hormones: ACTH from the pituitary drives cortisol; angiotensin II and potassium drive aldosterone.
- The medulla is controlled by nerves: preganglionic sympathetic fibres synapse directly on its cells, which behave like a giant modified ganglion and release adrenaline into the bloodstream.
Quick-fire facts
- •Each gland weighs about 4–5 g in an adult
- •Cortex hormones are steroids (corticosteroids): mineralocorticoids (aldosterone), glucocorticoids (cortisol) and adrenal androgens
- •The medulla makes mostly adrenaline (epinephrine) and some noradrenaline (norepinephrine)
- •The cortex comes from embryonic mesoderm, the medulla from neural crest — two different tissues sharing one capsule
- •The adrenal glands have a very rich blood supply from three arteries on each side: superior, middle and inferior suprarenal arteries
- •Thomas Addison described 'disease of the supra-renal capsules' in 1855; John F. Kennedy is the famous Addison's sufferer
- •Cushing's syndrome is caused by too much cortisol; a phaeochromocytoma is a tumour of the medulla that floods the body with adrenaline
- •The adrenal glands are so named because they lie 'ad renes', next to the kidneys; 'suprarenal' means above the kidney
- •A large fetal adrenal cortex shrinks after birth and is largely replaced by the adult cortex
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