The urinary bladder, a muscular sac in the pelvis, is located just above and behind the pubic bone. An empty bladder is about the size and shape of a pear. All the liquids that are drunk go through the bladder. The bladder takes in the liquid in order for the body to work. The bladder works with the kidneys. Urine which is made in the kidneys travels down two tubes called ureters to the bladder. The bladder stores urine, allowing urination to be infrequent and voluntary. The kidneys clean the liquid we drink. This goes on till the bladder is too full to hold any more. The normal capacity of the bladder is 400 to 600 ml. At this point, it is roughly the size of a softball. The bladder then tells the brain that it needs to be emptied. Once this message is received to the brain, the muscles around the bladder start to squeeze and the bladder starts to contract. At the same time the bladder sends a message to the sphincters to relax and let the liquid pass.