Release of Antidiuretic Hormone from the Neurohypophysis

Abstract

Fig. 37 represents diagrammatically the items involved in the control by the neurohypophysis of the volume of the urine. Increase in the osmotic pressure of the circulating plasma stimulates “osmoreceptors” in the anterior hypothalamus. Stimulation of the osmoreceptors leads to stimulation of the supraoptico-hypophysial tract, the fibres of which arise from cells in the supraoptic and paraventricular nuclei of the hypothalamus and extend via the pituitary stalk into the neural lobe of the pituitary. Stimulation of this tract causes the release of antidiuretic hormone from its endings; the released hormone enters the blood stream and so reaches and exerts its antidiuretic action on the kidneys. The renal action of the antidiuretic hormone has already been described in the previous chapter; this chapter deals with the neurohypophysis and the factors which determine the release of the hormone.