The Human Brain : From Neurone to Nervous System


  1. Neurones are classified into types partly according to the transmitter they release at their synaptic endings on other nerve cells. Some nerve cells do something different - they secrete hormones at their nerve endings, i.e. a hormone is released into the blood stream and circulates through the heart to reach the target organ. Supraoptic neurones have axons that pass into the posterior pitutiary (neurohypophysis), and release vasopressin (antidiuretic hormone) into the general circulation, and this hormone acts on the kidney in the control of water balance.

  2. Other hypothalamic neurones release hormones (called releasing hormones or releasing factors) into capillaries in the hypothalamus. These capillaries are one part of a portal system: they join togther to form the pituitary portal vein, which in turn opens up into a second set of capillaries within the anterior pituitary (adenohypophysisis). This specialised system of blood vessels, the hypothalamo-hypophyseal portal system (the pituitary portal system), carries releasing hormones from the hypothalamic capillaries to the adenohypophysial capillariesof the anterior lobe of the pituitary gland, where the releasing factors regulate the secretion of anterior pituitary hormones. Neurosecretion is the process whereby neurones release hormones (releasing hormones) into the vascular system. In the neurohypophysis the release is directly into the systemic circulation, but in the hypothalamus the hormones are released into the pituitary portal system.

  3. Key Words: Pituitary Portal System; Releasing Hormones; Posterior Pituitary