The kidneys’ main role is to remove bloodborne waste and supply the body with fresh blood. A little more than one litre of blood, which is about one-fifth of the total amount of blood pumped by the heart, passes by the kidneys through renal veins every minute. The renal veins allow blood to flow back to the body once it has been cleaned. Each kidney has around one million tiny units, known as Nephrons. A tiny filter known as a glomerulus, which is connected to a tubule, makes each Nephron. The waste and fluids are removed from the blood as it moves through the kidneys. They are then absorbed by any fluid left as urine. The majority of the fluid is later returned to the blood.