The adrenal medulla is the inner core of each adrenal gland, wrapped inside the cortex. Unlike the cortex, it is not a typical endocrine gland — it is a modified sympathetic ganglion, developmentally derived from neural crest, and its cells are essentially specialized postganglionic sympathetic neurons that lost their axons and learned to dump hormones into the bloodstream instead.
At a glance
What it does
Delivers the systemic arm of the fight-or-flight response. When the sympathetic nervous system fires, preganglionic cholinergic fibers synapse directly on chromaffin cells in the medulla, which release pre-stored vesicles of catecholamines — about 80% epinephrine (adrenaline) and 20% norepinephrine (noradrenaline) — straight into adrenal venous drainage.
The effects are what you would expect from a system designed to prepare a body for sudden physical demand. Heart rate and contractility up. Bronchodilation. Vasoconstriction in skin and gut, vasodilation in skeletal muscle. Glycogenolysis in liver and muscle raises blood glucose. Lipolysis mobilizes fatty acids. Pupils dilate. Sweating. Mental arousal. The whole package is tuned for the seconds-to-minutes window of acute threat.
How it works
Chromaffin cells synthesize catecholamines from tyrosine through the sequence: tyrosine to DOPA (via tyrosine hydroxylase, the rate-limiting step) to dopamine to norepinephrine to epinephrine. The final step — methylation of norepinephrine to epinephrine by PNMT — is unique to the medulla and depends on local cortisol delivered through the intra-adrenal portal circulation from the overlying cortex. This is why the medulla sits inside the cortex rather than as a separate organ: the cortex gives it a high cortisol bath to support epinephrine synthesis.
Once secreted, catecholamines act on alpha- and beta-adrenergic receptors distributed across tissues. Epinephrine has stronger beta-2 activity (bronchodilation, skeletal muscle vasodilation), norepinephrine is predominantly alpha (vasoconstriction). Both are rapidly metabolized by catechol-O-methyltransferase and monoamine oxidase, and their urinary metabolites (metanephrines and vanillylmandelic acid) are measured diagnostically.
The medulla's circulating contribution is smaller than most people assume. Most norepinephrine tone in the body comes from sympathetic nerve terminals releasing it locally, not from the medulla dumping it into blood. The medulla matters most for the extra burst during acute stress and for the epinephrine that sympathetic nerve terminals do not produce in meaningful amounts.
When it goes wrong
The medulla has no common deficiency disease. Total bilateral adrenalectomy for other reasons removes the medulla without obvious catastrophe, because sympathetic nerves still handle tonic function. Patients need cortisol replacement after bilateral removal, but they do not need epinephrine replacement.
Pheochromocytoma is the classic medullary tumor — rare (roughly 1-8 per million per year) but important because it is a treatable cause of resistant hypertension, and because anesthesia or surgery without recognizing it can trigger lethal hypertensive crisis. Classic triad: headache, palpitations, diaphoresis, in a hypertensive patient. Diagnosis is plasma or urinary fractionated metanephrines, then imaging. Treatment is alpha-blockade first (usually phenoxybenzamine or doxazosin) before beta-blockade, then surgical resection. Roughly 10% are malignant, 10% are extra-adrenal (paragangliomas), and 30-40% are associated with germline mutations (MEN2, VHL, NF1, SDHx).
Neuroblastoma is a pediatric tumor arising from neural crest precursors, often in the adrenal medulla. It is one of the most common solid tumors of early childhood and has a prognosis ranging from spontaneous regression to rapidly fatal depending on genetic subtype and stage.
Interactions
Chronic psychological stress drives repeated sympathetic activation and incremental medullary output. Caffeine, nicotine, and stimulant drugs raise catecholamine effects directly or indirectly. Exercise transiently increases catecholamines in proportion to intensity — part of why intense training feels the way it does.
Beta-blockers block the cardiac and vascular receptors that catecholamines hit, which is why they blunt heart rate response to stress and exercise. They are the backbone of pheochromocytoma management only after adequate alpha-blockade, because giving a beta-blocker first to an unopposed alpha state can worsen hypertension by leaving alpha-mediated vasoconstriction unchallenged.
Honest take
The medulla is not the source of "chronic stress damage" in the way popular framing suggests. Sustained cortisol from the cortex does most of that damage. The medulla mostly does acute bursts, and the bursts themselves are not the problem in a healthy cardiovascular system. What is actually worth knowing: if you have resistant hypertension, episodic severe hypertension with sweating and palpitations, or a strong family history of endocrine tumors, ask about pheochromocytoma screening — it is one of the rare causes of hypertension that is potentially curable with surgery, and missing it can kill you on an operating table from something completely unrelated.
Sources
- Lenders et al., Journal of Clinical Endocrinology and Metabolism — Endocrine Society guideline on pheochromocytoma and paraganglioma.
- Goldstein, Adrenaline and the Inner World — review of catecholamine physiology.
- Eisenhofer et al., Pharmacological Reviews — catecholamine metabolism.