Excretion is the process of formation and excretion of urine. Excretion is important function of the body is to maintain the consistency of the content of various substances in the body, and in particular in the blood (water balance, and osmotic pressure, rn, etc), and removal of end products of metabolism.
Usually excretion Express the volume of urine ml allocated for the day (daily diuresis). For a day in an adult in normal conditions is allocated 1000-2000 ml of urine.
Excretion during the day is uneven. The main part of the urinary tract (4/5) falls on a daily period of rest for the night. Sometimes in heart failure, nesharnyi diabetes, and other observed change this ratio and the main part of the urinary excretions falls at night (nocturia).
The urine by the kidneys happens though unevenly, but continuously.
In the glomeruli is filtering liquid part of plasma, except macromolecular protein and formed elements, and the formation of primary urine (150 - 170 liters per day). Admission primary urine in the kidney glomeruli is determined by hydrostatic pressure of blood in bringing vessels and electoral glomerular permeability of the epithelium.
In the renal tubules processes of reabsorption (reabsorption of glucose, water, sodium, potassium, calcium, chlorine and other substances, the result is the ultimate urine. The reabsorption processes are determined by the laws of osmosis, diffusion and selective permeability kanalzeva epithelium.
The main regulator of process water reabsorption in the kidneys is antidiuretic hormone (ADH), produced by the anterior nuclei of the hypothalamus and accumulated in the posterior lobe of the pituitary. ADH enters the blood every time-under the impact of the increase of osmotic pressure of blood plasma in connection with loss of water by the body or insufficient intake, as well as under the influence of pain, anesthesia, injuries and other factors. Kidney stimulates the secretion of ADH enzyme hyaluronidase, destroying hyaluronic acid side structures distal nephron (collectively tubes). As a result of their permeability to water increases significantly and the water is heavily absorbed from the tubules in the blood. With abundant supply of water in a body selection of ADH Nada and thereby decreases reabsorption of water in the kidneys and urinary excretion is increased.
In the tubules can occur also processes secretions (e.g., urea at its significant increases in the blood).
The decrease of urine output (oliguria) may be caused by the limited introduction of water in the body, increase vnepochechny excretion of water through the skin, lungs and so on, as well as decrease the intake of salt and reduction education in it osmotically active products exchange. In cases of pathology may occur complete termination of the urinary tract (see Anuria), or a significant increase (see Polyuria).
Clinical research methods of the urinary tract are the measurement of the amount allocated for a certain time urine. Are applied special functional tests. For example, the value of the glomerular filtration rate is determined by the introduction of inulin or mannitol, and creatinine.
Given that the concentration of these substances in the blood plasma, the glomerular filtrate and end urine equal, is the formula: S · P = VU (volume of filtrate, R - concentration of inulin in plasma, V is the number of urine for 1 min, U - concentration of inulin in the urine); From = VU/P refers to the volume of blood plasma, cleansed of inulin for 1 min (so-called cleansing in norm is 100-120 ml/min).
Kanalzevu secretion is determined by introduction of deodrant or sodium salt paralingua acid. Is calculated by the formula S = V·W-Q·P (S - the number of detract allocated with secretiruemy urine, V is the number of urine for 1 min, W - concentration of detract in the urine, Q is the volume of primary urine, R - concentration of detract primary urine).