The hypothalamus and the pituitary gland

Abstract

This chapter discusses the hypothalamus and the pituitary gland vis-a-vis the reproductive function and gonadal development. It also discusses the hormones secreted by the hypothalamus and the pituitary gland. The hypothalamus and the pituitary gland play a vital role in the control of gonadal development and reproductive function. Peptide and glycoprotein trophic hormones—including hypothalamic releasing hormones and some of the anterior pituitary hormones—act by binding to specific receptors in the cell membranes on the surface of target cells. They do not enter the cells but stimulate intracellular activity by a variety of mechanisms. Several hypothalamic hormones are secreted directly from axon terminals in the median eminence into the highly innervated capillaries of the hypothalamus which drain into the portal vessels. The portal vessels supply the anterior lobe of the pituitary and thus deliver hypothalamic hormones to the anterior pituitary. It is possible that the blood also flows in the portal veins in a retrograde manner from the pituitary to the hypothalamus. The chapter presents the hypothalamic hormones one of which is the luteinizing hormone releasing hormone (LHRH). It is produced by hypothalamic neurones, particularly in the region of the arcuate nucleus, and secreted from axon terminals in the median eminence into the portal circulation in a pulsatile manner. TRH is a tripeptide which is produced in the hypothalamus, as well as in other parts of the brain, and is secreted into the portal vessels. It acts on cells of the anterior pituitary to stimulate the production of both thyroid stimulating hormone and prolactin.