The two kidneys are positioned on both sides of the spine behind the abdominal cavity, which is enclosed by the peritoneum. To guard against injury, they are located under the bottom ribs and surrounded by a fatty pillow. They are bean-shaped organs that vary in size slightly depending on body size and also underlying disease. Each kidney is about as big as a fist. On average, they are 10 cm high, 5 cm wide and 4 cm thick. A healthy kidney weighs about 120-200 g. The kidneys are vital organs. They are responsible for the removal of waste products from the body, the regulation of the composition of body fluids and the production of some hormones. Thus, their function is important for balancing the metabolism of your body. In the course of kidney disease, the kidneys may be partly or completely unable to fulfill these tasks. Kidney disease occurs when kidneys can no longer perform these functions at full capacity. Permanently reduced kidney function is referred to as chronic renal failure.