Which sequence correctly describes the activation of the HPA axis and the role of cortisol?

Which sequence correctly describes the activation of the HPA axis and the role of cortisol?

• A. Stress triggers adrenal medulla to release adrenaline directly, bypassing the hypothalamus, with cortisol as a secondary messenger.
• B. The hypothalamus releases cortisol directly; this activates the pituitary to release CRH; the adrenal glands then release ACTH.
• C. Stress triggers hypothalamus to release CRH, prompting pituitary to release ACTH, which stimulates the adrenal cortex to release cortisol; cortisol promotes energy availability and modulates immune responses, with negative feedback limiting further HPA activation.
• D. Cortisol increases immune activity and energy consumption, with positive feedback to the hypothalamus.

Answer: (C)

The HPA axis responds to stress through a chain: the hypothalamus releases CRH, which signals the pituitary to release ACTH, and ACTH then stimulates the adrenal cortex to secrete cortisol. Cortisol helps by increasing energy availability—promoting glucose production and mobilizing fuels—and by dampening immune responses. Importantly, cortisol exerts negative feedback: high cortisol levels feed back to the hypothalamus and pituitary to reduce CRH and ACTH release, limiting further activation. The adrenal medulla releasing adrenaline is part of a quicker, separate system (the sympathetic-adrenal pathway), not the HPA axis described here. The other statements misplace where cortisol comes from, mischaracterize its effects on the immune system, or describe a positive feedback that cortisol does not produce.

The HPA axis responds to stress through a chain: the hypothalamus releases CRH, which signals the pituitary to release ACTH, and ACTH then stimulates the adrenal cortex to secrete cortisol. Cortisol helps by increasing energy availability—promoting glucose production and mobilizing fuels—and by dampening immune responses. Importantly, cortisol exerts negative feedback: high cortisol levels feed back to the hypothalamus and pituitary to reduce CRH and ACTH release, limiting further activation. The adrenal medulla releasing adrenaline is part of a quicker, separate system (the sympathetic-adrenal pathway), not the HPA axis described here. The other statements misplace where cortisol comes from, mischaracterize its effects on the immune system, or describe a positive feedback that cortisol does not produce.