The hypophyseal portal system
(or hypothalamo-hypophyseal portal system
) is the system of blood vessels
that links the hypothalamus
and the anterior pituitary
. It allows endocrine
communication between the two structures. 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 only a few portal systems of circulation in the body; that is, it involves two capillary beds connected by venules.
mechanism for hormone transport via hypothalamoportal vessels:
- cells regulated by different nuclei in hypothalamus, ie: 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.