Video of a cow<unk> g Physiology The 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<unk> ecate. This urge to<unk> ecate 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 faeces is 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. Voluntary and involuntary control The external anal sphincter is under voluntary control whereas the internal anal sphincter is involuntary. In infants, the<unk>  occurs by reflex action without the voluntary control of the external anal sphincter.<unk>  is voluntary in adults. Young children learn voluntary control through the process of toilet training. Once trained, loss of control, called fecal incontinence, may be caused by physical injury, nerve injury, prior surgeries (such as an episiotomy), constipation, diarrhea, loss of storage capacity in the rectum, intense fright, inflammatory bowel disease, psychological or neurological factors, childbirth, or death. Sometimes, due to the inability to control one's bowel movement or due to excessive fear,<unk>  (usually accompanied by urination) occurs involuntarily, soiling a person's undergarments. This may cause significant embarrassment to the person if this occurs in the presence of other people or a public place. Posture The positions and modalities of<unk>  are culture-dependent. Squat toilets are used by the vast majority of the world, including most of Africa, Asia, and the Middle East. The use of sit-down toilets in the Western world is a relatively recent development, beginning in the 19th century with the advent of indoor plumbing.
Defecation
Inspissation
Fecal impaction
Subluxation
Rectal foreign body
Vesicointestinal fistula
Rectal douching
Evisceration 