The kidneys are organs located on either side of the spine, at the small of the back. Kidneys filter the blood and help balance water, salt, and mineral levels in the blood; they also produce hormones that help regulate blood pressure and blood supply.

Waste from the kidneys is carried out of the body in urine. Urine flows through tubes (ureters) to the bladder, where it is stored until a person is ready to urinate. The waste and urine then leave the bladder to exit the body through a tube called the urethra.