Kidneys are the chief excretory organs of vertebrates, including mammals.They are vitally important in maintaining appropriate body chemistry.
Location: The two kidneys , each weighing about 150 gms in an adult human, lie in the upper posterior part of the abdominal cavity, on either side of the vertebral column.
External Structure: The kidney is a dark red bean shaped structure, measuring about 10 cm in length, 5 cm breadth, and 9 cm in thickness. The outer surface of the kidney is convex and the inner, which faces vertebral column, concave. A depression, called hilus, is present on the concave side. The ureter originates from the hilus and joins the urinary bladder backwardly. The renal artery and renal vein pass in and out at the hilus.
The major role of kidney is as follows.
Functions of Kidney
1. Removal of metabolic wastes: Both nitrogenous and non nitrogenous metabolic wastes are filtered out of blood by kidneys for removal from the body.
2. Regulation of water balance: Kidneys secrete excess hypotonic urine if the body has excess water and hypertonic urine if the body has deficiency of water.
3. Regulation of pH: Kidneys regulate pH of the body fluids by removing the excess acid or base. The ions which take part in this regulation are H+ and HCO3-.
4. Regulation of Salt balance: A proper Na+ -K+ ion balance is a must for functioning of nerves, muscles and other cells. Kidney help in maintaining the same through their retention or excretion.
5. Fluid Homeostasis: Blood volume of the body is maintained through controlling the amount of fluid loss in urine.
6. Elimination of Extra materials: Extra vitamins, drugs, pigments, salts and toxic chemicals are flushed out of the body by the kidneys.
7. Regulation of Blood Pressure: Blood pressure is regulated through secretion or non secretion of renin.
8. Conservation of Water: Kidneys have a very high osmotic concentration in interstitial fluid of medulla, about 1200mosm/1l. This removes water from urine and conserves the same.
9. Erythropoietin is a hormone produced by juxtaglomerular cells in response to decreased RBC count. Erythropoietin stimulates bone marrow to increase the rate of erythropoiesis or formation of red blood corpuscles (RBC).