A modified sympathetic ganglion secreting adrenaline and noradrenaline into the blood
Expansion
The medulla is a modified sympathetic ganglion: chromaffin cells are postganglionic neurones without axons, innervated directly by preganglionic fibres, so they respond to acetylcholine.
Synthesis: tyrosine to DOPA to dopamine to noradrenaline to adrenaline. The final step requires PNMT, which is induced by the high cortisol concentrations arriving from the cortex through the portal sinusoids. This anatomical arrangement is why adrenaline is made almost exclusively here.
Output is about 80 per cent adrenaline, in contrast to sympathetic nerve endings, which release noradrenaline.
Phaeochromocytoma produces episodic headache, sweating, palpitations and hypertension. Diagnosis is by plasma or urinary metanephrines, which are produced continuously by tumour metabolism and so are more reliable than the catecholamines themselves, whose release is intermittent.
Treatment requires alpha blockade before beta blockade: giving a beta blocker first leaves alpha-mediated vasoconstriction unopposed and can precipitate a hypertensive crisis.