<Li> Growth hormone - releasing hormone (GHRH): regulates the release of growth hormone from the anterior pituitary; as the name suggests, its main function is to help control cell growth, metabolism, and reproduction </Li> <Li> Thyrotropin - releasing hormone (TRH): regulates the release of thyroid - stimulating hormone from the anterior pituitary; functions to mediate various responses in the thyroid gland, including additional hormone synthesis </Li> <P> Over - or under - function as well as insufficiencies of the hypothalamus or the pituitary gland can cause a negative effect on the ability of the hypophyseal portal system to exchange hormones between both structures rapidly . This can have major effects on the respective target glands, making it impossible for them to carry out their functions properly . Occlusions and other issues in the blood vessels of the hypophysial portal system can also cause complications in the exchange of hormones between the hypothalamus and the pituitary gland . </P> <P> The hypophyseal portal system also plays an important role in several diseases involving the pituitary and central nervous system . In several cases of hypophyseal and pituitary metastatic tumors, the portal system acts as the pathway for metastasis from the hypothalamus to the pituitary . That is, cancerous cells from the hypothalamus multiply and spread to the pituitary using the hypophyseal portal system as a means of transportation . However, because the portal system receives an indirect supply of arterial blood, tumor formation in the anterior pituitary is less likely than in the posterior pituitary . This is because the posterior pituitary is vascularized by direct arterial blood flow . Pituitary apoplexy is described as hemorrhaging or reduction of blood supply to the pituitary gland . The physiological mechanisms of this condition have not been clearly defined in current research . It has been suggested, nonetheless, that damage to the pituitary stalk leads to an obstruction of blood flow in the hypophyseal portal system and contributes to this defective state . In Erdheim - Chester Disease, cells of the immune system called histiocytes proliferate at an abnormal rate causing a plethora of symptoms and, in more severe cases, death . The disruption of the hypophyseal portal system has been implicated as the mechanism for several symptoms involving the central nervous symptom, most notably diabetes insipidus . </P>

The hypophyseal portal system connects the hypothalamus to the anterior pituitary and