The kidney is a paired organ. The bean-shaped kidneys are located below the diaphragm at the posterior abdominal wall between the level of the 12th thoracic vertebra to the third lumbar vertebra. They are surrounded by an adipose capsule. Each consists of a cortex, which contains the renal glomeruli, the renal medulla, the renal calices, and the renal pelvis.

The main task of the kidneys is to remove potentially harmful waste materials along with the minimum amount of water. Through a complicated filter system, urine is produced and secreted into the renal pelvis and carried to the bladder by the ureters.

Urophanic substances (uric acid, creatinine, and urea) and toxic substances are excreted into the kidneys. Through the deposition and re-uptake, the kidney regulates the body's salt and mineral content (sodium, potassium, calcium, magnesium, and phosphate, bicarbonate) as well as the acid-base balance (pH of the blood).

In addition, the kidney also produces hormones such as renin, which is responsible for short-term changes in blood pressure, erythropoietin, which is responsible for the formation of blood, and calcitriol, which is important for potassium metabolism. Every day, approx. 1500 litres of blood flow through the kidneys. Thus, the body's entire volume of blood (5–7 l) is transported through the organ up to 300 times per day.