Diagrammatic representation of the hypothalamo-pituitary regulatory system.
The products of the posterior pituitary are synthesised in the supraoptic and paraventricular nuclei (5). After packaging, they are transported as granules, by axoplasmic flow, to the nerve terminals in the posterior pituitary where they are released directly into the circulation to act as classical neurohormones on distant target sites. The mechanism of anterior pituitary hormone secretion is entirely different. The pituitary hormone-releasing or releasing-inhibiting hormones of the hypothalamus are synthesised within the nuclei of the hypothalamus (1-4) and transported to the median eminence from where they travel to the anterior pituitary via the dense capillary network and the long portal veins. These hypothalamic factors occupy specific receptors on pituitary cells and lead either to the release or inhibition of the pituitary hormones. Modified from Gay (1972); by courtesy of the American Fertility Society.
