Why does urination always coincide with bowel movement? (Why do you always pee when you take a sh it?)?

But not always the other way around?
Answer:
When you just pee, it is pushed out by one muscle within the bladder. When you go poo, a whole series of muscles located within the pelvic diaphragm (which cradles your colon, bladder, and uterus in girls) along with your abdominal muscles act to help push out the bowel movement which also puts pressure on your bladder which makes you have to pee as well.This is also the reason that pregnant women have to pee so often and also when women delivery babies, they usually pee and poo at the same time.MikeC

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A human body works in mysterious ways. It does one thing and later does a total different thing and that just the way it is.

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Huh, never thought about it before...but it's true! LOL...Got too much time on your hands??

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When u shitt, u put pressure on ur lower abdominal muscles, which in turn transmits pressure to ur sphincter muscle - this muscle lets urine out of ur urethra.
If this sph muscle - the last muscle that holds/stops/releases ur pee - is strong enough, u can shittt w/o peeing
Try it - u first hold ur peeee, then put pressure on ur bowels, but from higher muscles - added force from upper abdomin - but u wont clear it satisfactorily...

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