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a terminal structure of sensory nerves that reacts to changes, in the concentration of osmotically active substances, that is, to changes in osmotic pressure in the surrounding fluid. Osmoreceptors are found in various animal organs and tissues, such as the liver and pancreas. Impulses from osmoreceptors reach the divisions of the central nervous system that participate in the regulation of water-salt metabolism. Osmoreception is controlled by neurons of the supraoptic nuclei in the hypothalamus. These neurons can perceive fluctuations of as low as 1–2 percent in the osmotic pressure of plasma, and when the osmotic pressure increases, they elaborate the hormone vasopressin, which is stored in the hypophysis. Vasopressin, the antidiuretic hormone, alters the permeability of the walls of the renal tubules when it is released into the blood, thereby reducing the amount of urine excreted.