What is the HPA axis and its role in stress response?

• A. The hypothalamic-pituitary-adrenal axis; it triggers cortisol release in response to stress.
• B. The hippocampus-pituitary axis; it triggers adrenaline release.
• C. The autonomic nervous system; it triggers melatonin release.
• D. The limbic-thalamic axis; it triggers insulin release.

Answer: (A)

The HPA axis is a hormonal pathway that coordinates the body’s response to stress by linking the brain to the adrenal glands. When stress is perceived, the hypothalamus releases CRH, which signals the pituitary to secrete ACTH. ACTH then stimulates the adrenal cortex to release cortisol. Cortisol helps mobilize energy by increasing glucose availability, modulates metabolism, and can shift priorities away from nonessential functions to support immediate demands. It also helps regulate the immune system and inflammation to balance the response. Cortisol provides negative feedback by signaling the hypothalamus and pituitary to reduce CRH and ACTH production, helping to dial back the response when the stress has passed. This system works on a slower timescale than the quick adrenaline surge from the sympathetic nervous system but is crucial for sustained energy and adaptation to prolonged stress. Other options mix up mechanisms—adrenaline (epinephrine) is part of the fast autonomic response, melatonin comes from the pineal gland, and insulin release is governed mainly by the pancreas—so they don’t describe the HPA axis.