The main function of the kidneys is purifying the blood (haemopurification) and clearing the body of excess water and salts. This process produces urine. The urine is then transported from the kidneys via the ureters into the bladder.

Other tasks include regulating blood pressure, controlling the formation of red blood cells (haematosis), and the production of hormones and enzymes. Humans normally have 2 kidneys, one left and one right. They are positioned in the area of the flanks (lati), which is why with kidney diseases such as, e.g., kidney stones, the pain is often localized there. Since the kidneys perform a lot of tasks for the body, they are very well supplied with blood. About 1,800 litres of blood flow through the kidneys every day. The kidney is an organ treated by two medical disciplines: nephrology and urology. Nephrology is a subdiscipline of internal medicine. A nephrologist deals with the diagnosis and non-surgical treatment of kidney diseases. A urologist mainly focusses on surgical treatment options and procedures such as, e.g., the surgical removal of tumours or stones of the urinary-tract collection system. Due to the overlapping of urology and nephrology, the two disciplines closely co-operate.