ABSTRACT
Acting through the anterior lobe of the pituitary gland the hypothalamus is the hub of five neuroendocrine axes that regulate aspects of metabolism, reproduction, development, and growth. Neurons in several hypothalamic nuclei send their axons to the external zone of the median eminence and the tuberoinfundibular tract. These axons secrete hypo-physiotropic hormones into the hypothalamic-pituitary portal system which carries them into the anterior lobe. Each hypophysiotropic hormone acts on a particular population of cells in the anterior lobe, either exciting or inhibiting their secretion of a specific stimulating (trophic) hormone. Hypophysiotropic hormones that excite secretion are termed releasing hormones, those that inhibit are called release-inhibiting hormones. Trophic hormones of the anterior pituitary are secreted into the systemic circulation and have endocrine effects on target tissues, particularly endocrine glands (Table 1).
