The kidneys are bean-shaped, fist-sized organs located on either side of the spine, near the middle of the back. The main function of the kidneys is to remove waste products and excess water from the blood.
The kidneys process about 200 liters of blood every day and produce about two liters of urine. The renal artery is the main blood vessel that supplies blood to a kidney and its nearby adrenal gland and ureter. After passing through the hilum - the indented part of the kidney - , the renal artery divides ordinarily into two large branches, and each branch divides into a number of smaller arteries which bring blood to the nephrons. Nephrons are the functioning units of the kidney where the actual removal of wastes occurs.