Stress Response

The body’s coordinated, whole-body reaction to a threat or demand — a temporary shift of resources away from long-term maintenance and toward immediate survival.

Two waves

• The fast wave — within seconds, the sympathetic nervous system and a surge of adrenaline produce the “fight-or-flight” state: racing heart, quick breathing, fuel released, senses sharpened.
• The slow wave — over minutes, the HPA axis releases cortisol, which sustains the response — keeping fuel available and damping non-urgent functions.

Acute versus chronic

Short-term, the stress response is protective and self-limiting. Sustained chronic stress, with cortisol kept high, has costs — it can suppress immunity, digestion, growth, and reproduction, and contributes to disease.

Key idea

The stress response is, in a sense, regulation in reverse — a deliberate, temporary abandonment of homeostatic housekeeping to meet an emergency. Its value lies in being brief.