adrenal gland

Embryologically, the adrenal cortex arises from mesoderm while the medulla arises from neural crest cells (specialized postganglionic sympathetic neurons), giving the gland a dual origin and distinct function. The cortex is organized into three histologic zones: zona glomerulosa (outer, produces aldosterone under RAAS/angiotensin II and potassium regulation), zona fasciculata (middle, produces cortisol under ACTH/CRH control), and zona reticularis (inner, produces androgens like DHEA). Steroidogenesis uses cholesterol as substrate, with cytochrome P450 enzymes (e.g., 21-hydroxylase, 11β-hydroxylase, 17α-hydroxylase) catalyzing conversions—deficiencies in these enzymes cause congenital adrenal hyperplasia with characteristic hormone imbalances. The adrenal medulla contains chromaffin cells that convert tyrosine to dopamine, then to norepinephrine and epinephrine via PNMT (induced by cortisol from the adjacent cortex, illustrating a unique paracrine relationship). Clinically relevant conditions include Cushing syndrome (cortisol excess), Conn syndrome (primary hyperaldosteronism), Addison disease (primary adrenal insufficiency, often autoimmune, causing hyperpigmentation due to elevated ACTH/MSH), pheochromocytoma (catecholamine-secreting tumor arising from chromaffin cells, causing episodic hypertension, tachycardia, and diaphoresis), and adrenal incidentalomas. The glands are highly vascularized with a rich arterial supply (from the inferior phrenic, aorta, and renal arteries) and unique venous drainage (right adrenal vein drains directly into IVC; left adrenal vein drains into the left renal vein), which is clinically important for vein sampling in diagnosing hyperaldosteronism.