Hormones of the Hypothalamus and Pituitary Gland

Hormones of the Hypothalamus and Pituitary Gland
The pituitary gland, or hypophysis, is a small gland (0.5 g in humans) lying in a well-protected position between the roof of the mouth and floor of the brain (Figure 36-5). It is a two-part gland having a double embryological origin. The anterior pituitary (adenohypophysis) is derived embryologically from the roof of the mouth. The posterior pituitary (neurohypophysis) arises from a ventral portion of the brain, the hypothalamus, and is connected to it by a stalk, the infundibulum. Although the anterior pituitary lacks any anatomical connection to the brain, it is functionally connected to it by a special portal circulatory system. A portal circulation is one that delivers blood from one capillary bed to another (Figures 36-5 and 36-6). In this case, the portal circulation provides a link between neurosecretory cells of the hypothalamus and anterior pituitary gland.

Figure 36-5 Human hypothalamus and pituitary gland. The posterior lobe is connected directly to the hypothalamus by neurosecretory fibers. The anterior lobe is indirectly connected to the hypothalamus by a portal circulation (shown in red) beginning in the base of the hypothalamus and ending in the anterior pituitary.