Osmoreceptors are sensory receptors that detect changes in osmotic pressure and contribute to maintaining fluid balance in the body. They are primarily found in the hypothalamus and kidneys. It is important that the osmolarity of blood and fluids is closely monitored as changes could lead to water moving in or out of cells, affecting cell function and, in extreme cases of high osmolarity, causing cells to burst.
When the osmotic pressure of the blood rises, water moves down the osmotic gradient into the cell, causing the cell to swell. The reverse happens at a low osmotic pressure. This triggers neuronal signals to be sent to the hypothalamus to increase ADH release to raise the osmotic pressure of the blood or reduce ADH release to lower the osmotic pressure.