Hypophyseal portal system

The hypophyseal portal system is the system of blood vessels that link the hypothalamus and the anterior pituitary in the brain.

It allows endocrine communication between the two structures. It is part of the hypothalamic-pituitary-adrenal axis. The anterior pituitary receives releasing and inhibitory hormones in the blood. Using these, the anterior pituitary is able to fulfill its function of regulating the other endocrine glands.

It is one of two portal systems of circulation in the human body; that is, it involves two capillary beds connected in series by venules. The other is the hepatic portal system.

Hormone transport
Mechanism for hormone transport via hypothalamoportal vessels:
 * cells regulated by different nuclei in hypothalamus, i.e., neurons that release neurotransmitters as hormones in the connective link between the pituitary and the brain. Hypothalamic hormones stimulate the release of the respective hormone from the anterior pituitary gland.
 * ligands (in this case, hormones released by the hypothalamus to activate hormone release from the anterior pituitary) are picked up by blood vessels then taken to anterior pituitary where they are broken down and released back into blood vessels
 * before they are broken down, hypothalamoportal vessel acts as local route for blood flow directly from hypothalamus to anterior pituitary.