The sphincter is a unit that combines smooth muscles from the bladder neck and urethra and striated muscles from around the urethra. When it becomes convenient to urinate, another message is sent for the sphincter to open and the bladder to contract. These actions must coordinate for successful urination. Women are more likely to have bladder control problems than men because of their anatomy. In women, the bladder, bladder neck, and urethra are partially supported by the vagina and the striated muscles of the pelvic floor.
Muscle tone weakens with childbirth, age, and significant weight gain.
Changes in muscle support will allow the bladder and urethra to shift and can affect continence. In addition, a woman's urethra is shorter, approximately 3 to 5 cm, compared with about 23 cm for a man's urethra. Therefore, men have a longer area of urethral compression to resist bladder pressure when the bladder wants to contract. This is directly related to estrogen's effects. As estrogen levels decrease, the urethra loses its ability to compress.