Biochemistry

the air in the alveoli at body temperature is saturated with water vapor. Up to 1 liter of water is lost through the skin through perspiration and evaporation. A small part of the water - 0.2 liters - is excreted through the food channel along with feces. The amount of water released by the body can vary significantly depending on environmental conditions, the work performed and the condition of the body. So, in a hot climate, water release during sweating increases significantly (up to 4-5 liters). With intensive work, an increase in body temperature, due to an increase in the volume of respiration, the secretion of water through the lungs increases. The central nervous system, in particular, its departments such as the cerebral cortex, the diencephalon, and the medulla oblongata, as well as many endocrine glands, is actively involved in the regulation of water metabolism. Some hormones secreted by the endocrine glands contribute to the retention of water in the body, while others, on the contrary, stimulate its secretion. The regulation of water metabolism is based on maintaining a constant osmotic pressure, and the main regulatory system for water metabolism is the “ hormones - kidneys ” system. Of the hormones involved in the regulation of water metabolism, first of all, the hormone of the posterior pituitary gland - vasopressin and the hormone of the adrenal cortex - aldosterone, should be distinguished. Vasopressin causes a reduction in the renal vessels, resulting in decreased diuresis (urination), and consequently, the release of water from the body. Therefore, vasopressin is often called the antidiuretic hormone. The secretion of this hormone is regulated by the osmotic pressure of blood plasma. An increase in pressure stimulates the production of vasopressin, which reduces the excretion of water from the body by increasing the water-holding capacity of tissues and by increasing the excretion of concentrated urine. As a result of this, the osmotic pressure decreases, the irritation of the neurohypophysis is reduced, and the secretion of vasopressin is stopped. The effect on water metabolism of aldosterone is associated with the level of sodium in blood plasma. The decrease in osmotic pressure and the excretion of water and, therefore, diluted urine in large quantities is associated with a decrease in the concentration of sodium in blood plasma. A decrease in sodium levels causes an increased secretion of aldosterone, which enhances the reverse absorption of sodium in the kidneys and thereby delays it in the body. An increase in plasma sodium levels inhibits the secretion of this hormone. Thus, the different mechanisms of action of these two hormones depend on the osmotic pressure of the plasma, a decrease in which leads to increased secretion of aldosterone and inhibition of the production of vasopressin. With an 23