adrenal medulla

The adrenal medulla is the inner core of the adrenal gland, buried beneath the cortex. While the cortex makes slow steroid hormones, the medulla is built for speed: it is the body's hormonal alarm bell, releasing a surge of catecholamines into the blood within seconds of a perceived threat. If the cortex is a chemical factory, the medulla is a fire-alarm pull station wired straight into the nervous system.

Functionally, the medulla acts like a giant modified sympathetic ganglion. Its hormone-secreting cells, called chromaffin cells, are essentially neurons without axons. When the sympathetic nervous system is activated, it stimulates these cells directly, and they dump epinephrine (about 80 percent of output) and norepinephrine straight into the bloodstream, broadcasting the fight-or-flight signal body-wide.

This catecholamine surge raises heart rate, dilates airways, redirects blood to muscles, and mobilizes glucose — all the changes needed for sudden exertion. The medulla is not strictly necessary for life (unlike the cortex), but a tumor of its chromaffin cells, called a pheochromocytoma, can cause dangerous catecholamine surges with severe high blood pressure.