Q.Explain briefly how the hypothalamus regulates the secretions of the anterior pituitary through its releasing and inhibiting hormones.

[!TLDR]

The hypothalamus sends releasing hormones (switch a pituitary hormone ON) and inhibiting hormones (switch one OFF) to the anterior pituitary via a local portal blood system.

[!ANSWER]

Hypothalamic releasing hormones (e.g. TRH, GnRH, CRH, GHRH) stimulate, and inhibiting hormones (e.g. somatostatin, dopamine/PIH) suppress, specific anterior pituitary hormone secretions, carried there via the hypothalamo-hypophyseal portal blood vessels.

The hypothalamus regulates the anterior pituitary using a set of small peptide hormones, collectively called hypophysiotropic hormones, released by hypothalamic neurosecretory cells into the hypothalamo-hypophyseal portal system -- a short, local network of blood vessels that carries them directly to the anterior pituitary at high concentration, bypassing dilution in the general circulation. Releasing hormones stimulate secretion of a specific anterior pituitary hormone: for example, TRH stimulates TSH release, GnRH stimulates FSH/LH release, CRH stimulates ACTH release, and GHRH stimulates GH release. Inhibiting hormones instead suppress a specific secretion: somatostatin suppresses GH release, and prolactin-inhibiting hormone (dopamine) suppresses prolactin release. By adjusting the balance of these releasing and inhibiting signals, the hypothalamus can independently turn each anterior pituitary hormone's output up or down.

[!ANSWER]

Hypothalamic releasing hormones (e.g. TRH, GnRH, CRH, GHRH) stimulate, and inhibiting hormones (e.g. somatostatin, dopamine/PIH) suppress, specific anterior pituitary hormone secretions, carried there via the hypothalamo-hypophyseal portal blood vessels.

State the two functional classes (releasing vs inhibiting) and the delivery route (local portal blood vessels, not general circulation or nerve axons) that distinguishes anterior pituitary control from posterior pituitary control.

Describing hypothalamic control of the anterior pituitary as happening via direct nerve connection -- that direct-axon route is how the hypothalamus controls the POSTERIOR pituitary; the anterior pituitary is controlled via the portal BLOOD system instead.