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. Author manuscript; available in PMC: 2011 Aug 29.
Published in final edited form as: Endocr Dev. 2010 Dec 16;20:116–126. doi: 10.1159/000321232

Figure 1.

Figure 1

Organization of the HPA axis.

The PVN center of the HPA axis receives circadian inputs from the SCN and stress-related and other regulatory inputs from multiple brain and peripheral sites. CRH and AVP are secreted into the hypophyseal portal system and transported to the anterior pituitary gland where they synergistically stimulate ACTH secretion. ACTH released into the systemic circulation stimulates the zona fasciculata of the adrenal cortices to secrete cortisol or corticosterone in humans and rodents, respectively. The “master” circadian pacemaker of the SCN, thus, produces a circadian rhythm of glucocorticoid concentrations in the blood. Importantly, this site of the brain does not have GR and, hence, is not influenced by circulating glucocorticoids. (Modified from [16]) ACTH: adrenocorticotropic hormone, AVP, arginine-vasopressin, CRH: corticotropin-releasing hormone, F/B: cortisol/corticosterone, PVN: paraventricular nucleus, SCN: suprachiasmatic nucleus