Urinary control also depends on a seal mechanism inside the urethra that works together with, but independent of, the outside sphincter. This internal seal mechanism acts like a washer in a water faucet. With the internal seal mechanism and outside sphincter muscles working together, the urethra is able to seal and unseal itself. In female stress urinary incontinence, increased pressure on the bladder from ordinary physical activities, such as lifting, sneezing, coughing, or laughing, results in leakage from the bladder. Most of the time, the condition is the result of weakened pelvic muscles, which are supporting the bladder, bladder neck, and urethra.
Pelvic muscles can weaken because of pregnancy, childbirth, and prior pelvic surgery.
This weakened support may cause the bladder neck and urethra to shift from their normal positions. Once out of position, they may drop momentarily when there is pressure on the bladder from an activity such as coughing. This downward movement can cause the bladder neck and urethra to open briefly, resulting in urine leakage. The medical term used by urologists for this condition is urethral hypermobility or too much movement of the urethra. Another less common cause for female stress urinary incontinence is called intrinsic sphincteric deficiency, which is the result of weakened urethral sphincter muscles along with loss of the internal seal effect inside the urethra.