Editing Defecation (section)

===Physiology===
{{Further|Rectum#Function}}
The [[Rectal ampulla|rectum ampulla]] stores fecal waste (also called stool) before it is excreted. As the waste fills the rectum and expands the rectal walls, stretch receptors in the rectal walls stimulate the desire to defecate. This urge to defecate arises from the reflex contraction of rectal muscles, relaxation of the [[internal anal sphincter]], and an initial contraction of the skeletal muscle of the [[external anal sphincter]]. If the urge is not acted upon, the material in the rectum is often returned to the colon by [[reverse peristalsis]], where more water is absorbed and the feces are stored until the next mass peristaltic movement of the transverse and descending colon.

When the rectum is full, an increase in pressure within the rectum forces apart the walls of the [[anal canal]], allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves push the feces out of the rectum. The internal and external anal sphincters along with the [[puborectalis muscle]] allow the feces to be passed by muscles pulling the anus up over the exiting feces.<ref>{{cite web |url=https://medicine.umich.edu/sites/default/files/content/downloads/bowel-function.pdf |title=Bowel Function Anatomy |publisher=University of Michigan Health System |accessdate=2021-05-19 |quote=The levator ani and the puborectalis need to coordinate properly in order to expel contents from the anal canal. }}</ref>