HYPOPHYSEAL PORTAL SYSTEM
Hypothalamic hormones that release or inhibit anterior pituitary hormones reach the anterior pituitary via a portal system.
In the hypophyseal portal system, blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary.
The superior hypophyseal arteries (branches of the internal carotid arteries) bring blood into the hypothalamus and the infundibulum
These arteries divide into a capillary network called the primary plexus of the hypophyseal portal system
From the primary plexus, blood drains into the hypophyseal portal veins that pass down the outside of the infundibulum
In the anterior pituitary, the hypophyseal portal veins divide again and form another capillary network called the secondary plexus of the hypophyseal portal system
Above the optic chiasm neurosecretory cells synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles
Which reach the axon terminals and nerve impulses stimulate the vesicles to undergo exocytosis
The hormones then diffuse into the primary plexus of the hypophyseal portal system then, the hypothalamic hormones flow with the blood through the portal veins and into the secondary plexus.
Hormones secreted by anterior pituitary cells pass into the secondary plexus capillaries, which drain into the anterior hypophyseal veins and out into the general circulation
Anterior pituitary hormones then travel to target tissues throughout the body