Negative feedback loops regulate hormone secretion

In addition to being controlled by hypothalamic releasing and release-inhibiting hormones, the endocrine cells of the anterior pituitary are also under direct and indirect negative feedback control by the hormones of the target glands they stimulate (see Figure 40.7). For example, cortisol, produced by the adrenal gland in response to ACTH secreted by the anterior pituitary, reaches the pituitary in the circulating blood and inhibits further release of ACTH. Cortisol also acts as a negative feedback signal to the hypothalamus, inhibiting the release of corticotropin-releasing hormone (CRH). Because cortisol is the final hormone released in this chain of interacting structures called the hypothalamic–pituitary–adrenal axis, its feedback actions are called long-loop negative feedback. In this system, the tropic hormone ACTH also exerts negative feedback control on the hypothalamic cells that produce the corresponding releasing hormone (CRH). This action is called short-loop negative feedback because of the proximity of the pituitary and the hypothalamus.