Kidney

The kidney belongs to the urinary system.

Function of the kidney

The kidney is involved in several processes although its main function is to detoxify the body by removing waste in urine. It filters blood plasma and is responsible for homeostasis (the balance of water and ions) in the body. Diuresis or urine output (urine formation) is 1.5 litres daily.

The kidneys have glands in the upper part of the organ called the adrenal glands that have an endocrine function: they secrete hormones (erythropoietin, corticosteroids, adrenaline). The kidneys also control blood pressure

The two kidneys are essential organs although it is possible to live with only one.

Structure of the kidney

There are two kidneys, located in the abdomen. They are ovoid in shape with a convex external surface. Their average size is 2 centimetres long, 6 cm wide and 3 centimetres thick. The renal artery branches and divides further within the kidney itself in the cavity in the internal part of the kidney known as the renal sinus.

The kidneys are surrounded by a very hard protective membrane. Internally, the kidney is formed from a cortex on the periphery and a central part, the medulla. The cortex passes into the medulla extending to the sinus.

The basic part of the kidney is the nephron. Each kidney has approximately 1 million of these. Overall, each nephron contains all of the parts required to filter blood. This occurs in the blood capillaries (glomerulus) surrounded by the Bowman's capsule. Each capsule is directly connected to a long tubule which ends in the calices, which in turn pour urine into the pelvis (also called the pylon) and then into the ureter.