sympathoadrenal system

The sympathoadrenal system is the fast arm of the stress response, formed by joining the sympathetic nerves with the adrenal medulla into a single rapid-action unit. When danger strikes, this system can flood the body with adrenaline in seconds, long before the slower cortisol pathway gets going. It is the wiring behind the surge you feel when you are suddenly startled.

Anatomically, the adrenal medulla is in effect a modified sympathetic ganglion: nerve fibers from the spinal cord travel directly to it and trigger the release of catecholamines, mostly adrenaline, straight into the blood. At the same time, the sympathetic nerves release noradrenaline locally onto the heart, blood vessels, and other organs. The two routes work in concert to raise heart rate, blood pressure, and blood glucose and to ready the muscles for action.

The sympathoadrenal system pairs with the HPA axis to form the two limbs of the stress response, fast catecholamines and slower cortisol. A tumor of the adrenal medulla, a pheochromocytoma, hijacks this system, causing dangerous surges of catecholamines with pounding headaches, sweating, and spiking blood pressure.