How it works

                                                                    

When you eat something your body takes as much as it needs, then whatever the body doesn't need it sends it to the excretory system. Your body needs to balance the amount of water, food and anything else your body needs or else the excretory system would be almost useless and your body would have to much stuff left over. First your blood goes into your kidneys and the kidneys act like a strainer and takes a substance called urea from the blood as the blood passes through and then the urea/urine goes down a tube called the ureter and the urine goes into your bladder were it stays until the bladder gets emptied and the urine goes down a tube called the urethra and out of your body completely. The bladder doesn't empty right away instead it holds the urine until your ready to go to the bathroom. But your bladder doesn't stay the same size, it swells when it's full and it shrinks when it's emptied. If your bladder emptied every time urine came into it you would have to go to the bathroom a lot.