When your bladder is full, you have the sensation of needing to pass urine. This sensation occurs through the nerves in the bladder wall. When you pass urine, your sphincter muscle relaxes while your bladder wall muscles contract and the urine passes out through a tube called the urethra . You can increase the pressure on the bladder by contracting the muscles of your abdomen and pelvis to help expel the urine. Any disorders that involve the urinary tract and the nerves controlling it can cause urinary incontinence.
Incontinence is very common and occurs about twice as often in women as in men.
This is because the muscles of the pelvic floor are weakened during childbirth and, after the menopause, a lack of the hormone oestrogen causes a weakened urethra. Childbirth may also cause damage to the sphincter, urethra and nerves of the bladder. Pelvic surgery may also be a cause of similar damage to these structures. All these problems cause reduced resistance to the flow of urine. Therefore, urinary incontinence in women tends to increase with age and is more common after childbirth and pelvic surgery.