How do you spell that? venlafaxine and weight changes The bladder sits near the bottom of the pelvis and is a storage device for urine. âThe bladder can expand like a balloon depending on how much urine itâs storing,â says Galsky. âThe bladder expands until a signal is sent to the brain that it needs to empty and you urinate. If you didnât have a bladder, youâd have to urinate all the time.â