Each of your kidneys is made up of about a million filtering units called nephrons. Each nephron has a glomerulus to filter your blood and a tubule that returns needed substances to your blood and pulls out additional wastes. Wastes and extra water become urine.
Your kidneys remove wastes and extra fluid from your body. Your kidneys also remove acid that is produced by the cells of your body and maintain a healthy balance of water, salts, and minerals—such as sodium, calcium, phosphorus, and potassium—in your blood.
Blood flows into your kidneys through the renal artery and exits through the renal vein. Your ureter carries urine from the kidney to your bladder.