Pelvic floor reflex and continence when intra-abdominal pressure rises
The pelvic floor (a funnel-shaped sheet of muscle closing the bottom of the pelvis) contracts by reflex when abdominal pressure rises, supporting the urethra to keep urine in.
Remember
In a healthy adult, a cough triggers a reflex contraction of the pelvic floor that supports the pelvic organs and squeezes the urethra shut; a weak or delayed response has been linked to leakage (stress urinary incontinence, which is leakage when abdominal pressure rises).
Memory aid
the abdominal wall pushes, the pelvic floor holds
Picture the abdominal wall muscles creating the rise in pressure while the pelvic floor holds against it.
Coughing, sneezing and laughing suddenly raise intra-abdominal pressure (the pressure inside the abdominal cavity). That pressure is passed on to the bladder and pushes urine towards the urethra. To stay dry, the urethra has to close harder at that moment.
Continence means being able to hold urine and stool until we choose to pass them. In continent women, the cough reflex activates the pelvic floor muscles. They give the urethra extra support, so it is compressed and better able to stay closed against the pressure. A reflex is a fast, automatic response that happens without conscious effort.
Timing matters. The contraction needs to happen in step with the pressure rise, and delayed responses during coughing have been linked to stress urinary incontinence. This is leakage when abdominal pressure rises, as with a cough or a laugh. Urgency incontinence is different: it is leakage with a sudden, intense urge to pass urine. In one small study the reflex was absent in women with stress urinary incontinence.
At rest the pelvic floor stays in gentle, constant contraction, called tonic contraction. This supports the pelvic organs and helps keep the urethra and anus closed, and the muscles relax when we pass urine or stool. The detrusor (the smooth muscle of the bladder wall) works the other way: it stays relaxed while the bladder fills and contracts to empty it.
Childbirth, age and chronically raised abdominal pressure can weaken the pelvic floor. Pelvic floor exercises, which strengthen the muscles by squeezing them, are used to treat stress incontinence.
Key facts
- Trigger
- coughing, sneezing and laughing suddenly raise intra-abdominal pressure.
- Normal response
- the pelvic floor contracts by reflex, supporting the pelvic organs and compressing the urethra.
- Timing
- the contraction needs to happen in step with the pressure rise, and delayed responses have been linked to stress urinary incontinence.
- At rest
- tonic contraction of the pelvic floor supports the pelvic organs and helps keep the urethra closed when we are not trying to pass urine.
- Source of the pressure
- the abdominal wall muscles, which squeeze the abdominal contents, create the rise, and the pelvic floor holds against it.
- Weakness
- childbirth, age and chronically raised abdominal pressure can weaken the pelvic floor.
Exam traps
- Relaxing the external urethral sphincter (a ring of muscle around the urethra) does not protect against a cough, because this muscle stays contracted while urine is stored and relaxing it would cause a leak.
- A reflex detrusor contraction does not help during a cough, because it raises bladder pressure and promotes emptying, whereas continence needs urethral pressure to exceed bladder pressure.
- A contraction that comes late does not protect, because it has to keep pace with the pressure rise and a late contraction would allow leakage.
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