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The urinary bladder is an organ in the human body. It is the part of our urinary system. 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. The kidneys clean the liquid we drink. This goes on util the bladder is too full to hold any more. 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.