BIOCHEMISTRY - Main Regulators and Biological Fluids of the Human Body - 2016

4. CHEMICAL COMPOSITION OF URINE

4.3. Regulation of Urine Formation

The urine-forming function of the Kidneys is controlled by neurohormonal regulation. The most important Hormones governing urine production are aldosterone and vasopressin.

Aldosterone (an adrenocortical hormone) increases The rate of sodium ion reabsorption in the renal tubules. Simultaneously, the reabsorption of chloride ions and Water is accelerated, resulting in a decreased urine volume.

Vasopressin (a hypothalamic hormone), also known as the antidiuretic hormone, likewise reduces urine volume by increasing the permeability of the renal tubule walls to water (enhancing its reabsorption).

The regulation of Urine Formation is also carried out through the synthesis of hormone-like Proteins—renin and Erythropoietin—in the kidneys.

Renin is produced in response to a drop in Blood pressure. Decreased blood pressure has a negative impact on ultrafiltration. This protein is a proteolytic enzyme that converts one of the Blood Plasma Proteins into angiotensin, a biologically active substance that stimulates aldosterone synthesis. This leads to increased reabsorption of sodium chloride (NаСI) and water, thereby increasing the circulating blood volume and raising blood pressure in the vascular glomeruli.

Erythropoietin is synthesized when oxygen supply to the kidneys is impaired (anemia, blood loss). Carried by the bloodstream to the Cytology/practical/86.html">Red Bone Marrow, it stimulates hematopoiesis, which ultimately improves the oxygen supply to the kidneys. Due to this stimulating effect on blood Cell production, erythropoietin has recently been used as a doping agent in endurance sports requiring high aerobic capacity.