Osmotic pressure is the force with which a dissolved substance holds or attracts water.A large number of homeostatic constants, including vital ones, directly depends on intensity of water- salt exchange: blood pressure level, urine output and respiration intensity, pH of blood and all internal mediums content of a body.In other words, water-salt metabolism in the body ensures implementation of all other substances exchange, formation of membrane potentials and the course of excitable processes and, consequently, of homeostasis maintenance.In its turn, the movement of water through membrane creates conditions for transmembrane transport of all other substances; nutrient substances - inside cells, metabolism products - out of them.Therefore, osmotic pressure is one of the rigid homeostatic constant, because cells, tissues and organs systems functions can be implemented only in condition of osmotic pressure stability