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