1 · Acute stress — the HPA cascade fires
In acute stress, the axis fires in sequence, CRH to ACTH to cortisol, and cortisol mobilizes glucose and heightens vigilance, meant to switch on briefly, then off.The stress response is not the enemy — it is a life-saving adaptation. The slow axis (hypothalamic-pituitary-adrenal) fires in sequence: hypothalamic CRH → pituitary ACTH → adrenal-cortex cortisol.In acute stress cortisol mobilizes glucose to fuel brain and muscle, heightens vigilance, and temporarily shuts down non-urgent systems (digestion, reproduction, parts of immunity). It is designed to switch on briefly, then off.