Water is the main part of blood, digestive juices, and cell structure, so its balance is vital for the body.
Water is the medium in which various chemical reactions of metabolism occur, and it is a powerful solvent for many chemical compounds (salts, sugars, alcohols, acids, and others). Digestion processes occur only in the aqueous environment, and absorption of nutrients into the blood appears. Toxic substances are removed from the body in aqueous solutions with urine and bile.
Water metabolism is under the control of neurohormonal regulation. The feeling of thirst controls the inflow of exogenous water into the body. Thirst arises when the percentage of water and nutrients in the body is reduced even by a few percent. The primary hormone that causes water retention in the body is vasopressin.
This hormone is produced by the hypothalamus, stored in the posterior lobe of the pituitary gland, and from it is released into the blood. Under the influence of vasopressin in the kidneys, the reabsorption of water from primary urine into the bloodstream is accelerated, resulting in decreased diuresis and water retention.