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the anteroposterior curve or angle, with convesity directed anteriorly, of the anorectal junction; tonus of the puborectalis (muscle) produces the angle for maintaining fecal continence; relaxation of the muscle allows the angle to be reduced for defecation.
The sharp forward bend at the anorectal junction as the rectum passes through the pelvic diaphragm muscles. This acute bend, which is normally maintained by the puborectalis sling muscles, helps to keep feces in the rectum. During defecation the pelvic diaphragm muscles relax (so the puborectalis sling relaxes) and the sharp bend between rectum and anus straightens; this makes the passage of feces from rectum to anus easier.
See also: flexure