Inside each kidney are approximately one million tiny units called nephrons . Nephrons filter and remove the excess fluid and waste products from the blood. The excess fluid and waste products filtered out of the kidneys are excreted as urine, which travel though tubes called ureters into the bladder. The bladder is the storage sac for urine. Urine is eventually carried from the body through the urethra , a tube-like structure leading to the opening from which you urinate.
Healthy kidneys can remove about one to two quarts of urine a day.
Normal working kidneys have other jobs too. They make chemicals called hormones that help you to make red blood cells, build strong bones, and keep your blood pressure under control. When kidneys are healthy and functioning normally, these major kidney functions will continue. Our survival depends on these vital organs, even though you can live a normal life with only one kidney. When kidneys fail, waste products that are harmful to your body build up and make you feel sick.