11.4 : Physiological Foundation of Stress

Stress triggers a coordinated physiological response involving the sympathetic nervous system (SNS) and the hypothalamic-pituitary-adrenal (HPA) axis. This dual activation ensures that the body is prepared for both immediate and prolonged stress management. The process begins with the perception of a stressor. This initial phase activates the SNS, leading to the rapid release of adrenaline (epinephrine) from the adrenal glands.

Role of the Sympathetic Nervous System

Adrenaline triggers the classic "fight-or-flight" response, characterized by an increased heart rate, elevated respiration, and heightened blood flow to skeletal muscles. This rapid response prepares the body to either confront the stressor or flee from it. For instance, encountering a threat like an aggressive animal triggers an instant SNS response, enabling the individual to react swiftly by either fighting back or running away.

Activation of the HPA Axis

While the SNS initiates an immediate response, the HPA axis takes a more gradual approach. Stress signals activate the hypothalamus to release corticotropin-releasing factor (CRF), which prompts the anterior pituitary to secrete adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH then stimulates the adrenal cortex to produce glucocorticoids, primarily cortisol. Cortisol, often called the "stress hormone," is vital for prolonging the body's stress response by modulating glucose metabolism, suppressing non-essential functions like digestion and growth, and maintaining blood pressure. For example, prolonged psychological stress at work, such as working to meet a deadline, can elevate cortisol levels, ensuring a sustained energy supply and adaptation to the ongoing demand.

This intricate system, involving the rapid actions of adrenaline and the longer-lasting effects of cortisol, ensures that the body is optimally prepared to respond to both immediate and sustained stressors, maintaining homeostasis during challenging situations.