Intra-rectal pressure builds as the fills with feces, pushing the feces against the walls of the . Contractions of abdominal and pelvic floor muscles can create intra-abdominal pressure which further increases intra-rectal pressure. The (an involuntary muscle) responds to the pressure by relaxing, thus allowing the feces to enter the canal. The rectum shortens as feces are pushed into the anal canal and push the feces out of the rectum. Relaxation of the internal and external anal sphincters allows the feces to exit from the anus, finally, as the muscles pull the anus up over the exiting feces.

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