Chapter 19 - Pituitary Function

Abstract

The hypothalamus-pituitary system is a preeminent example of integration of neural and endocrine control. It consists of three major systems such as neuroendocrine system connected to an endocrine system by a portal circulation, a neurosecretory pathway, and a direct neural regulation of endocrine secretion. The neuroendocrine system involves clusters of peptide- and monoamine-secreting cells in the anterior and midportion of the ventral hypothalamus. Their products reach the median eminence by axonal transport. From there, they are released into the capillary vessels of the hypothalamus-pituitary portal system and transported to the pituitary to regulate the secretion of hormones from the anterior lobe of the adenohypophysis. The neurosecretory pathway runs from the anterior hypothalamus, traverses the floor of the ventral hypothalamus, and terminates in the neural lobe of the neurohypophysis on fenestrated blood vessels. The system is involved in osmoregulation through the production and release of vasopressin and in parturition and nursing through the secretion of oxytocin. In the intermediate lobe (IL) the secretory activity is regulated via direct neuronal inhibitory and stimulatory influences. The function of IL cells in mammals has not been fully established, but they may play a role in opioid-regulated functions.