Glucocorticoid

Glucocorticoids are a class of steroid hormones produced by the adrenal cortex that regulate metabolism, immune function, and the body's response to stress. Cortisol is the primary glucocorticoid in humans; corticosterone predominates in rodents. These hormones mediate many of the effects attributed to the HPA axis, serving as the system's effector arm: they translate neural and hormonal signals into physiological action across virtually every tissue in the body.

Glucocorticoids operate through two receptor types — mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) — which function as ligand-activated transcription factors. When bound by hormone, these receptors translocate to the nucleus and modulate gene expression, producing the slow genomic effects that underlie long-term adaptation to stress. But glucocorticoids also produce rapid non-genomic effects through membrane-associated receptors and second-messenger systems, operating on timescales of minutes rather than hours.

The hormone's dual-receptor, dual-timescale architecture makes it a remarkably versatile signaling molecule — and a dangerous one when chronically elevated. Sustained glucocorticoid exposure produces allostatic load: hippocampal atrophy, immune suppression, metabolic dysregulation, and increased cardiovascular risk. The same molecule that saves the organism during acute threat becomes toxic when the threat never resolves.