Science Fair Project Encyclopedia
Defecation or feceation (known colloquially as pooping or shitting (slang) or having a "bowel movement") is the act of eliminating solid or semisolid waste material from the digestive tract. Humans remove waste anywhere from several times daily to a few times weekly; sloths can go for a week or more without eliminating. Waves of muscular contraction known as peristalsis in the walls of the colon move fecal matter through the digestive tract towards the rectum. Undigested food ma also be expelled this way, this process is called egestion.
The rectum ampulla (anatomically also: ampulla recti) acts as a temporary storage facility for the waste material. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed. If defecation is delayed for a prolonged period the fecal matter may harden, resulting in constipation.
When the rectum is full the increase in intrarectal pressure forces the walls of the anal canal apart allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincters of the anus allow the feces to be passed by muscles pulling the anus up over the exiting feces.
During defecation the chest muscles, diaphragm, abdominal wall muscles, and pelvic diaphragm all exert pressure on the digestive tract and respiration temporarily ceases as the lungs push the chest diaphragm down in order to exert pressure. Blood pressure rises throughout the body and the amount of blood pumped by the heart decreases. Death has been known to occur in cases where defecation causes the blood pressure to rise enough to cause the rupture of an aneurysm or to dislodge blood clots (see thrombosis).
Defecation may be involuntary or under voluntary control. Loss of control may be caused by physical injury, intense emotions, impaired water absorption in the colon (see diarrhea), and psychological or neurological factors. See fecal incontinence for a discussion of this.
The positions and modalities of defecation are culture-dependent . In some countries, like Turkey and Japan, it is customary to squat (thus squat toilets), while in most of the Western World sit-down toilets are used. Similarly, the anus and buttocks may be cleared with toilet paper, or with water (compare bidet).
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