Suprarenal Gland Anatomy
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Direct answer
Suprarenal, literally "above the kidney", describes two glands that are really two endocrine organs in one capsule: a yellow, lipid-rich cortex of mesodermal (coelomic epithelial) origin arranged in the glomerulosa, fasciculata and reticularis zones, and a chromaffin medulla derived from neural crest cells that is effectively a modified sympathetic ganglion. The right gland is triangular or pyramidal and caps the upper pole, relating medially to the inferior vena cava; the left is semilunar and lies on the medial aspect of the upper pole, behind the stomach and pancreas. Each weighs about 4 grams and receives a striking three-source arterial supply — superior from the inferior phrenic, middle directly from the aorta, inferior from the renal artery — yet drains through a single vein: the short right vein enters the IVC directly, while the left vein joins the left renal vein.
What you must remember
- Dual embryology: cortex from intermediate mesoderm (coelomic epithelium); medulla from neural crest chromaffin cells that migrate in — the medulla is innervated by preganglionic sympathetic fibres (T5–T11 splanchnic nerves) without a second neuron.
- Cortex zones, GFR: glomerulosa makes aldosterone (salt), fasciculata cortisol (sugar), reticularis androgens (sex) — "the deeper you go, the sweeter and sexier it gets" is the tolerable mnemonic.
- Medulla output: roughly 80 per cent adrenaline, 20 per cent noradrenaline, released directly into the blood on sympathetic stimulation — the gland of the fight-or-flight response.
- Three arteries, one vein: superior (inferior phrenic), middle (aorta), inferior (renal); right suprarenal vein short and direct to the IVC — avulsed easily at surgery — left vein to the left renal vein.
- Right versus left shape: right triangular among the liver, IVC and kidney; left semilunar, crescenting the medial border of the upper pole; both lie inside the renal fascia but separated from the kidney by a septum.
- Pheochromocytoma, rule of 10s: roughly 10 per cent extra-adrenal (paraganglioma, as in the organ of Zuckerkandl), 10 per cent bilateral, 10 per cent familial (MEN 2, VHL), 10 per cent malignant, 10 per cent in children — "the 10 per cent tumour".
- Indian clinical context: tuberculosis remains the commonest cause of primary adrenal insufficiency in India, unlike autoimmune Addison's disease in Western series — a favourite differential in medicine vivas.
Working through a suspected pheochromocytoma
A young adult with paroxysmal headache, palpitations and drenching sweats, hypertensive between attacks, walks the adrenal anatomy from ward to theatre. Urinary or plasma metanephrines confirm excess catecholamine production; CT or MRI locates the tumour — and in 10 per cent it is not in the gland at all but in the sympathetic chain or the organ of Zuckerkandl near the aortic bifurcation, which is why the rule of 10s exists. Before surgery, alpha-blockade with phenoxybenzamine precedes beta-blockade, because blocking beta-mediated vasodilatation first leaves unopposed alpha vasoconstriction and hypertensive crisis. At operation the venous anatomy decides difficulty: the right vein is short, wide and direct into the IVC, and tearing it is the operation's signature catastrophe; on the left the vein is ligated safely at the left renal vein. Bilateral tumours in MEN 2 remind the surgeon that cortex-sparing adrenalectomy exists, because leaving cortical tissue spares the patient lifelong steroid dependence.
How the exam frames it
Viva examiners return to the same three junctions. "Why is the medulla supplied by preganglionic fibres?" — because chromaffin cells are modified postganglionic sympathetic neurons that never grew axons; they release transmitter into blood instead of a synapse. "Why does Waterhouse-Friderichsen syndrome destroy both glands at once?" — meningococcal septicaemia causes bilateral adrenal haemorrhage, and the glands' rich arterial supply with a single venous outlet creates a vulnerable vascular bed. And "which single vein does the surgeon fear?" — the right suprarenal vein, whose short course into the IVC explains why right-sided adrenalectomy bleeds. Candidates who connect embryology (neural crest), histology (chromaffin) and surgery (vein length) in one breath usually end the viva early — in the good sense.
Frequently asked questions
What are the three sources of arterial supply to the suprarenal gland?
Superior suprarenal arteries from the inferior phrenic, middle suprarenal arteries directly from the abdominal aorta, and inferior suprarenal arteries from the renal artery.
How does the venous drainage differ on the two sides?
The right suprarenal vein drains directly and briefly into the inferior vena cava; the left suprarenal vein drains into the left renal vein.
Which cortical zone secretes aldosterone and which cortisol?
The zona glomerulosa secretes aldosterone (sodium retention), the zona fasciculata cortisol (glucose metabolism and stress response), and the zona reticularis androgens.
What is the embryological origin of the adrenal medulla?
Neural crest chromaffin cells, making it a modified sympathetic ganglion innervated by preganglionic fibres — hence its rapid, nerve-triggered secretion.
State the rule of 10s for pheochromocytoma.
Roughly 10 per cent are extra-adrenal, 10 per cent bilateral, 10 per cent familial, 10 per cent malignant and 10 per cent occur in children.