Adrenal medulla
Ganglion · Greater splanchnic T5–T9 N_N on chromaffin cells 80% adrenaline
A modified sympathetic ganglion: neural crest chromaffin cells are postganglionic neurones without axons. Preganglionic fibres of the greater (and lesser) splanchnic nerves pass through the coeliac plexus without synapsing and release acetylcholine onto nicotinic receptors, triggering exocytosis of catecholamines into the blood.
Traced from the start
Detail
- Innervation
- Preganglionic cholinergic fibres only — the one sympathetic target reached without a peripheral postganglionic neurone
- Secretion
- Adrenaline ~80%, noradrenaline ~20% (small amounts of dopamine); PNMT converting noradrenaline to adrenaline is induced by cortisol from the cortex
- Half-life
- Circulating catecholamines last about 1–2 minutes (COMT and MAO)
When it goes wrong
Phaeochromocytoma (10% bilateral, extra-adrenal, malignant or familial — MEN2, VHL, NF1) releasing catecholamines episodically
Paroxysmal headache, sweating, palpitations and hypertension; diagnose with plasma free metanephrines; give α-blockade (phenoxybenzamine) before any β-blocker or unopposed α vasoconstriction causes hypertensive crisis
Practise this structure
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