Читать книгу Essential Endocrinology and Diabetes - Richard I. G. Holt - Страница 26

Negative feedback is the commonest form of regulation used by biological systems. For example, in enzymology, the product frequently inhibits its own catalyzed reaction. In endocrinology, a hormone may act on its target cell to elicit a response (often secretion of another hormone) that then inhibits production of the original hormone (Figure 1.4a). The same effect can come from a metabolic process. For instance, the pancreatic β‐cell makes insulin in response to high surrounding glucose levels. The effect is to lower glucose, which, in turn, inhibits further insulin production. The hypothalamic–anterior pituitary–end organ axes are a slightly more complex extension of this model. The hypothalamic hormone [e.g. corticotrophin‐releasing hormone (CRH)] stimulates release of the anterior pituitary hormone (e.g. ACTH), which, in turn, increases peripheral hormone production (e.g. cortisol). The peripheral hormone then feeds back via the circulation to inhibit further production of the anterior pituitary and hypothalamic hormones. Figure 1.4b illustrates the anterior pituitary and end‐organ components of this model where hormone 1 could be ACTH and hormone 2 could be cortisol.