This MedLibrary.org supplementary page on Defecation is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! i want a big fat boner in my ass!~!!!! ]] by which organisms eliminate solid, semisolid or liquid waste material (feces) from the digestive tract via the anus. Humans expel feces with a frequency varying from a few times daily to a few times weekly; sloths can go a week without expellingcitation needed. 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 may 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 unneeded material. As the rectal walls expand due to the material filling it, stretch receptors from the nervous system located 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 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. If defecation is delayed for a prolonged period the fecal matter may harden, resulting in constipation.
When the rectum is full, an increase in intra-rectal 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 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.
Defecation is normally assisted by taking a deep breath and trying to expel this air against a closed glottis (Valsalva maneuver). This contraction of expiratory chest muscles, diaphragm, abdominal wall muscles, and pelvic diaphragm exert pressure on the digestive tract. Ventilation at this point temporarily ceases as the lungs push the chest diaphragm down in order to exert the pressure. Thoracic blood pressure rises and as a reflex response 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). Also, in release of the Valsalva maneuver blood pressure falls, this coupled often with standing up quickly to leave the toilet results in a common incidence of blackouts in this situation.
When defecating, the external sphincter muscles relax. The anal and urethal sphincter muscles are closely linked, and experiments by Dr. Harrison Weed at the Ohio State University Medical Center have shown that they can only be contracted together, not individually, and that they both show relaxation during urinationcitation needed. This explains why defecation is frequently accompanied with urination.
Defecation may be involuntary or under voluntary control. Young children learn voluntary control through the process of toilet training. Once trained, loss of control causing fecal incontinence may be caused by physical injury (such as damage to the anal sphincter that may result from an episiotomy), intense fright, inflammatory bowel disease, impaired water absorption in the colon (see diarrhea), and psychological or neurological factors.
The positions and modalities of defecation are culture-dependent. In some regions of the world, such as South Asia, East Asia and rural parts of the Middle East, it is customary to squat (typically using squat toilets), while in most of the Western World sit-down toilets are used.
The anus and buttocks may be cleansed with toilet paper, similar paper products, or other absorbent material. In some cultures water is used (e.g. as with a bidet) either in addition or exclusively. In Japan, some toilets known as washlets are designed to wash and dry the anus of the user after defecation (see anal cleansing).
References
- Deeb, Benjamin (2004). "Healthy to the Core: How to Measure Effective Defecation." Greenwood Press.
- Widmaier, Raff, Strang (2006). "Vanders Human Physiology, the mechanisms of body function. Chapter 15. McGraw Hill.
Wikipedia content modification information:
- This page was last modified on 6 July 2008, at 22:26.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Defecation".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.