Question

Discuss hypothalamic–pituitary–adrenal (HPA) axis function in the context of stress response?

Answer 1

 Stress disrupts homeostasis in the body and provokes a response that is coordinated by hypothalamic–pituitary–adrenal (HPA) axis. The stress response is directed towards returning the body back to homeostasis. Different stressors - physical, psychological etc., activate central HPA Axis through diverse routes that depend on the type of stressor. These routes include catecholaminergic route and 'limbic system' route. A crucial crossing in this response system is the paraventricular nucleus of the hypothalamus (PVN).

For all input signals induced by stressors and which ultimately set in motion the HPA Axis, paraventricular nucleus of the hypothalamus (PVN) serves as the converging point. Different excitatory (norepinephrine/serotonin) as well as inhibitory signals (GABA/ opioids) act on the PVN and modulate the HPA axis function. PVN releases neurohormones - CRH and arginine vasopressin (AVP) – into hypophysial portal blood. In the anterior pituitary they stimulate the adrenocorticotropic hormone (ACTH) production and secretion. ACTH through blood circulation reachs to adrenal glands and induces glucocorticoid production and release there. Cortisol is the main glucocorticoid in humans whereas it is corticosterone in rodents. Glucocorticoids in turn inhibit the activity of HPA axis through negative-feedback mechanism. This complex system, in which glucocorticoids themselves check their own levels, performs key function of regulated stress response and body's return back to homeostasis

This complex HPA axis system, in which glucocorticoids released check their own levels, performs key function of regulated stress response and body's return back to homeostasis