Your kidneys basically "cleans" any liquid that you drink, what is waste goes to your bladder and what is healthy and has items that your body needs it sends it into the blood stream, the circulatory system. So when a failure happens it means the kidney is failing to to do its job of cleaning, sending harmful items in your bloodstream that can effects your organs and the heart. In the excretory system, the urine may turn out a dark color or you may not be able to pee at all.
