Posterior Pituitary Hormones

Abstract

The hypothalamus (Fig. 1) embodies a group of nuclei that form the floor and ventrolateral walls of the triangular-shaped third ventricle. A thin membrane called the lamina terminalis forms the anterior wall of this compartment and contains osmoreceptor cells in a structure known as the organum vasculosum. The subfornical organ (SFO) also contains osmoreceptors. The organum vasculosum of the lamina terminalis (OVLT), the SFO, and the pituitary gland lack a blood-brain barrier. The supraoptic nucleus lies just dorsal to the optic chiasm and approx 2 mm from the third ventricle. The para-ventricular nucleus lies closer to the thalamus in the suprachiasmatic portion of the hypothalamus, but it borders on the third ventricular space. These well-defined nuclei contain the majority of the large neuroendocrine cell bodies, known as the magnocellular or neurosecretory cells, that manufacture arginine vasopressin (AVP) and oxytocin (OT). The neurohypophysis consists of (1) a set of hypothalamic nuclei, the supraoptic and paraventricular nuclei, which house the pericarya of the magnocellular neurons; (2) the axonal processes of the magnocellular neurons that form the supraoptical hypophyseal tract; and, (3) the neurosecretory material of these neurons, which is carried on to the posterior pituitary gland (Fig. 1).