Definition
Glucocorticoids are steroid hormones released by the adrenal glands in response to stress; in humans the principal one is cortisol. Their job during a crisis is to mobilize energy — raising blood glucose, sharpening attention, and diverting resources away from long-term projects like growth, digestion, and immune defense.
Sapolsky, whose own research career centered on stress hormones, treats glucocorticoids as a textbook case of a dose-dependent, time-dependent molecule. Briefly elevated, they are lifesaving. Chronically elevated, they become slow poison.
Why it matters
How it works
A stressor activates the hypothalamic-pituitary-adrenal axis: the hypothalamus signals the pituitary, which signals the adrenal glands to secrete glucocorticoids. Normally the rising hormone feeds back to shut the cascade down. Under chronic stress that brake fails — the hippocampal neurons that mediate the feedback are themselves damaged by prolonged exposure, so the system loses its off switch and the damage compounds.