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Anatomy of the anus and rectum

Defecation is the act or process by which organisms eliminate solid, semisolid or liquid waste material (feces) from the digestive tract via the anus^{[citation needed]}. Humans expel feces with a frequency varying from a few times daily to a few times weekly^{[citation needed]}; sloths can go a week without expelling^{[citation 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. Image File history File links Question_book-3. ... Image File history File links This is a lossless scalable vector image. ... Diagram of the rectum and anus. ... For other uses, see Waste (disambiguation). ... Horse feces Feces, faeces, or fæces (see spelling differences) is a waste product from an animals digestive tract expelled through the anus (or cloaca) during defecation. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... This article is about the bodily orifice. ... This article is about modern humans. ... This article is about the South American mammal. ... For other uses of Muscle, see Muscle (disambiguation). ... Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ... It has been suggested that this article or section be merged with Large intestine. ... The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. ...

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. The rectum is about 12 cm. ... The nervous system is a highly specialized network whose principal components are nerves called neurons. ... It has been suggested that this article or section be merged with Large intestine. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Constipation or irregularity, is a condition of the digestive system where a person (or animal) experiences hard feces that are difficult to egest; it may be extremely painful, and in severe cases (fecal impaction) lead to symptoms of bowel obstruction. ...

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. The anal canal is the terminal part of the large intestine. ... Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ... The Sphincter ani internus (or internal anal sphincter) is a muscular ring which surrounds about 2. ... The Sphincter ani externus (external anal sphincter) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. ... This article is about the bodily orifice. ...

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. In medicine, the Valsalva maneuver is performed by forcibly exhaling against closed lips and pinched nose, forcing air into the middle ear if the Eustachian tube is open. ... Male Chest The chest is a part of the anatomy of humans and various other animals. ... In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. ... The pelvis (pl. ... In respiratory physiology, ventilation is the rate at which gas enters or leaves the lung. ... A sphygmomanometer, a device used for measuring arterial pressure. ... Post surgical photo of brain aneurysm survivor. ... For other uses, see Blood (disambiguation). ... Thrombosis is the formation of a clot or thrombus inside a blood vessel, obstructing the flow of blood through the circulatory system. ...

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 urination^{[citation needed]}. This explains why defecation is frequently accompanied with urination. Manneken Pis of Brussels. ...

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. Toilet training (or potty training) is the process of weaning a young child off diapers (or nappies in the British Isles and many Commonwealth countries) and training the child to use the toilet for urination and defecation. ... Fecal incontinence is the loss of regular control of the bowels. ... The Sphincter ani externus (external anal sphincter) is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. ... Medio-lateral episiotomy as baby crowns. ... In medicine, inflammatory bowel disease (IBD) is a group of inflammatory conditions of the large intestine and, in some cases, the small intestine. ... In medicine, diarrhea, also spelled diarrhoea (see spelling differences), refers to frequent loose or liquid bowel movements. ... Psychology (ancient Greek: psyche = soul and logos = word) is the study of mind, thought, and behaviour. ... Neurology is a branch of medicine dealing with disorders of the central and peripheral nervous systems. ...

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. For other uses, see Culture (disambiguation). ... Map of South Asia (see note on Kashmir). ... This article is about the geographical region. ... A map showing countries commonly considered to be part of the Middle East The Middle East is a region comprising the lands around the southern and eastern parts of the Mediterranean Sea, a territory that extends from the eastern Mediterranean Sea to the Persian Gulf. ... French Squatter toilet A squat toilet is a toilet used by squatting, rather than sitting. ... Occident redirects here. ... For other uses, see Toilet (disambiguation). ...

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). This article is about the bodily orifice. ... Bottom commonly refers to the human buttocks but also has other uses. ... This article or section does not cite any references or sources. ... For the South Park episode, see Toilet Paper (South Park episode). ... A toilet (left) and a bidet (right). ... A cleansing jet of water designed to wash the anus of the user of this bidet-style toilet. ... This article or section does not cite any references or sources. ...

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.