Biochemistry

color of the skin of animals changes, which is associated with the induction of tyrosine oxidation into the melanin pigment . The posterior pituitary gland secretes vasopressin and oxytocin . They are synthesized in special cells of the hypothalamus. From there, they are transported by neurons to the posterior pituitary gland and enter directly into the blood. Vasopressin (antidiuretic hormone, ADH) increases blood pressure and promotes the reabsorption of water in the capillaries of the renal tubules, and therefore reduces urination. An important link in the mechanism of this process is the activation of hyaluronidase, which breaks down the mucopolysaccharide hyaluronic acid and thereby increases the permeability of the cell membranes of the renal tubules. With insufficient formation of vasopressin, diuresis is enhanced (up to 10 1 of urine in 1 day). This disease is called diabetes insipidus. Oxytocin increases the tone of smooth muscles, especially the uterus and muscle fibers of the mammary gland. Hormone of the parathyroid glands. Parathyroid hormone (parathyroid hormone) regulates the content of calcium ions and anions of phosphoric and citric acids in the blood. With a prolonged deficiency of calcium salts in food or with a violation of its absorption from the intestine, the concentration of calcium in the blood decreases. This leads to increased synthesis and secretion of parathyroid hormone , which helps to wash out (in the form of nitrates and phosphates) calcium salts from bones. Another target organ of parathyroid hormone is the kidney, in which it reduces phosphate reabsorption in the tubules and increases calcium reabsorption. The point of application of the action of parathyroid hormone is the receptor proteins of the plasma membrane of target cells and the activation of adenylate cyclase dependent on them. As a result of this, redistribution of calcium occurs in the components of the cell between tissues and organs. Hormones of the thymus ( thymus or thymus gland ). By the time of puberty, to a large extent, it undergoes a reverse development. It synthesizes the hormones thymosins and thymopoietins . They participate in the function of some parts of the immune system (T-lymphocytes), and also regulate the growth processes of the child's body. Pancreatic hormones. In the islet part of the pancreas (islets of Langerhans), the hormones insulin and glucogon are synthesized . Insulin (a protein hormone) is produced in the p-cells of the pancreas from its precursor, proinsulin. The insulin that enters the bloodstream lowers the glucose content in the blood, i.e., it has a hypoglycemic effect . The action of insulin on a cell is manifested primarily in its interaction with receptor proteins located on the outer surface of the plasma membrane. It is believed that the formed receptor ­ insulin complex reacts with other components of the membrane, which leads to a 285