Figure 11.

The HPG and HPA neuroendocrine axes are shown. For each system, a group of hypothalamic neurons synthesizes and secretes a neuropeptide, CRH (HPA axis) or GnRH (HPG axis). These hormones travel through the portal capillary vasculature between the base of the hypothalamus and the anterior pituitary. There, CRH activates the synthesis and secretion of ACTH from corticotropes. Similarly, GnRH stimulates LH and FSH release. These pituitary hormones, when they reach their target glands (adrenal or gonad), regulate steroidogenic processes involved in biosynthesis of the glucocorticoids and sex steroid hormones. These hormones activate stress and reproductive responses, respectively, in the body. They also exert feedback actions on the hypothalamus and pituitary to enable adaptation of the body and to modulate homeostasis of these neuroendocrine systems.