Figure 1.

Components and Secretagogues of the HPA Axis. A. With sufficient input, neurons in the paraventricular nucleus (PVN) of the hypothalamus release corticotrophin releasing hormone (CRH) into the portal system connecting the anterior pituitary (B.), causing adrenal corticotrophin hormone (ACTH) to be released into the general circulation. C. Adrenal cortical cells respond to ACTH by producing and releasing the steroid cortisol, which is distributed throughout the body via the general circulation. D. One of cortisol’s many functions is to provide negative feedback through receptors located in the hypothalamus and pituitary, thus keeping HPA axis activity in check.