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The circular folds slow the passage of the partly digested food along the intestines, and afford an increased surface for absorption. [5] They are covered with small finger-like projections called villi (singular, villus). Each villus, in turn, is covered with microvilli. The microvilli absorb fats and nutrients from the chyme.
The circular muscle layer prevents food from travelling backward and the longitudinal layer shortens the tract. The thickness of the muscular layer varies in each part of the tract: In the colon, for example, the muscular layer is much thicker because the faeces are large and heavy and require more force to push along.
Circular folds are transverse folds that slow the passage of the luminal contents and serve to expand the total surface area threefold. Villi and intestinal glands serve to increase the mucosal surface area tenfold. (Intestinal villus) Microvilli covering the apical surface of the enterocytes increase the absorptive surface twentyfold.
These folds are about 12 mm. in width and are composed of the circular muscle coat of the rectum. They are usually three in number; sometimes a fourth is found, and occasionally only two are present. One is situated near the commencement of the rectum, on the right side.
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus.The GI tract contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines.
The external anal sphincter is far more substantial than the internal anal sphincter. The proximal portion of external anal sphincter overlaps the internal anal sphincter (which terminates distally a little distance proximal to the anal orifice) superficially; where the two overlap, they are separated by the intervening conjoint longitudinal muscle.
It appears rounded and is often covered by a fold on the uppermost side of the papilla; that is, the side which receives contents from the stomach. [4] The major duodenal papilla is seen from the duodenum as lying within a mucosal fold. The minor duodenal papilla is situated 2 cm proximal. [2]
The internal anal sphincter is the specialised thickened terminal portion of the inner circular layer of smooth muscle of the large intestine. It extends from the pectinate line (anorectal junction) proximally to just proximal to the anal orifice distally (the distal termination is palpable). Its muscle fibres are arranged in a spiral (rather ...