The kidneys are a pair of bean-shaped organs, each about the size of a person’s fist. They are situated in the back of the abdominal cavity behind the peritoneum on each side of the spine, and are partly protected by the lower ribs. Their ability to sustain adequate function through ageing, illness or injury is considerable.
It is occasionally discovered that a person has only one kidney. This does not generally cause any problems as long as the kidney in question is working properly.
The kidneys are part of the urinary system, and have several important functions. The production of urine and the removal of toxic waste products are the most recognized of these, while the regulation of electrolyte concentration levels and acid-base balancing are less well-known. The kidneys also secrete certain substances (hormones, enzymes) into the blood: erythropoietin is necessary for the production of red blood cells; renin regulates blood pressure; and vitamin D is needed for the absorption of calcium in the intestine, thus playing an important role in bone anabolism.
The capacity of the kidneys to clean the blood can be followed by measuring creatinine clearance, which is normally around 120 ml/min. However, kidney function may deteriorate quite significantly before any symptoms are detected. As a result, clearance levels may be significantly affected when kidney failure is finally diagnosed.