The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys filter waste from the blood to produce urine. Each kidney contains approximately 1 million nephrons, the functional units that filter blood. The kidneys regulate fluid and mineral balance, produce hormones, and remove wastes from the body. When the kidneys fail to function, renal replacement therapies such as hemodialysis, peritoneal dialysis, or kidney transplantation are needed.