stresssystem

The stresssystem is the integrated network of neural and hormonal pathways that enables an organism to respond to perceived threats or demands. It involves the central nervous system, the autonomic nervous system, and the neuroendocrine system, and it operates on multiple time scales from seconds to hours and days.

A central component is the hypothalamic-pituitary-adrenal (HPA) axis. Perception of stress activates the hypothalamus to release corticotropin-releasing hormone (CRH), which signals the anterior pituitary to secrete adrenocorticotropic hormone (ACTH). ACTH then stimulates the adrenal cortex to produce glucocorticoids, chiefly cortisol in humans. Cortisol helps mobilize energy, modulates metabolism, and supports adaptive behavior. The HPA axis is regulated by negative feedback: rising cortisol inhibits CRH and ACTH release to limit the response.

The autonomic nervous system, particularly the sympathetic branch and the adrenal medulla, provides a rapid, short-term response known as the fast or sympathetic-adrenal system. It releases catecholamines (adrenaline and noradrenaline), increasing heart rate, blood pressure, and glucose availability to prepare for quick action. The parasympathetic system counterbalances these effects to return the body to baseline when the threat passes.

Brain networks involved include the amygdala, which detects threat, the prefrontal cortex that modulates responses, and the hippocampus that relates stress to memory. Stress hormones also interact with the immune system, sometimes suppressing or modifying inflammatory processes.

Chronic activation of the stresssystem, or allostatic load, can contribute to health problems such as cardiovascular disease, metabolic disorders, sleep disturbances, anxiety, and depression. Coping mechanisms, social support, sleep, and physical activity can mitigate adverse effects and promote resilience.