Why can you pee without pooing, but you can't poo without peeing?
We asked a GP so you don’t have to.
The passage of our bodily waste is controlled by circular muscles called sphincters. The external sphincters are under our control. The sphincter around the urethra is smaller than the one around the anus, so when you decide to urinate you can relax it without relaxing the whole pelvic floor. This means you can pass urine without needing to pass stool at the same time.
When you do pass stool however, the relaxation of the stronger anal sphincter also decreases tension in the weaker urinary sphincter, allowing urine to pass at the same time. But this isn’t always the case – it is possible, but difficult, to do one without doing the other.
Asked by: Kate Selby, Dundee
Read more:
- Why is poo always brown, no matter what we eat?
- Is there really poo everywhere?
- Why does coffee make me need a poo?
- Why does running water make me need the toilet?
To submit your questions email us at questions@sciencefocus.com (don't forget to include your name and location)
Authors
Dr Nish Manek is a GP in London. She completed her medical degree at Imperial College and was runner-up in the University of London Gold Medal. Manek has also developed teaching courses for Oxford Medical School, and has penned articles for The Guardian and Pulse magazine.
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