In humans the urinary bladder is a triangular muscular bag that temporarily stores urine before voiding.
It lies anterior to the rectum in the male and anterior to the vagina in females. In both sexes it lies behind the pubic symphysis.
The mucosa (inner lining) of the bladder is transitional epithelium with rugae. The folds (rugae) allow it to expand as it fills. As it fills with urine, stretch receptors steadily increase the urge to pee.