The bladder is the organ that stores the urine excreted by the kidneys for its urination and it has capacity for approximately 300-350 ml. It is situated on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. The urine flow from the bladder is controlled by the detrusor muscle (located in the wall of the bladder), and by two sphincters: a voluntary one and an involuntary one (but if the top capacity of the bladder is reached, the voluntary one become involuntary and the urine is ejected).