BLADDER, DRAWING. BLADDER, DRAWING The urinary bladder is part of the urinary system situated in the lower part of the pelvis. This spherical pouch stores urine produced continuously by the kidneys. When the bladder is full, it contracts, evacuating urine via the urethra when the sphincter is open. Different bladder diseases are common (infection, tumor, stones). Cancer of the bladder is favored by smoking. Here is a sagittal section of the bladder shown in blue.