small intestine

intestine (def. 2).
[1760-70]

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Long, narrow, convoluted tube in which most digestion takes place.

It extends 22–25 ft (6.7–7.6 m), from the stomach to the large intestine. The mesentery, a membrane structure, supports it and contains its blood supply, lymphatics, and insulating fat. The autonomic nervous system supplies it with parasympathetic nerves that initiate peristalsis and sympathetic nerves that suppress it. It is lined with minute fingerlike projections (villi) that greatly increase its surface area for enzyme secretion and food absorption. Its three sections, the duodenum, jejunum, and ileum, have distinct characteristics. Food takes three to six hours to pass through the small intestine unless a disorder such as gastroenteritis, diverticulosis, or obstruction impedes it.

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 a long, narrow, folded or coiled tube extending from the stomach to the large intestine; it is the region where most digestion and absorption of food takes place. It is about 6.7 to 7.6 metres (22 to 25 feet) long, highly convoluted, and contained in the central and lower abdominal cavity. A thin membranous material, the mesentery, supports and somewhat suspends the intestines. The mesentery contains areas of fat that help retain heat in the organs, as well as an extensive web of blood vessels. Nerves lead to the small intestine from two divisions of the autonomic nervous system: parasympathetic nerves initiate muscular contractions that move food along the tract ( peristalsis), and sympathetic nerves suppress intestinal movements.

      Three successive regions of the small intestine are customarily distinguished: duodenum, jejunum, and ileum. These regions form one continuous tube, and, although each area exhibits certain characteristic differences, there are no distinctly marked separations between them. The first area, the duodenum, is adjacent to the stomach; it is only 23 to 28 cm (9 to 11 inches) long, has the widest diameter, and is not supported by the mesentery. Ducts from the liver, gallbladder, and pancreas enter the duodenum to provide juices that neutralize acids coming from the stomach and help digest proteins, carbohydrates, and fats. The second region, the jejunum, in the central section of the abdomen, comprises about two-fifths of the remaining tract. The colour of the jejunum is deep red because of its extensive blood supply; its peristaltic movements are rapid and vigorous, and there is little fat in the mesentery that supports this region. The ileum is located in the lower abdomen. Its walls are narrower and thinner than in the previous section, blood supply is more limited, peristaltic movements are slower, and the mesentery has more fatty areas.

      The mucous membrane lining the intestinal wall of the small intestine is thrown into transverse folds called plicae circulares, and in higher vertebrates minute fingerlike projections known as villi (villus) project into the cavity. These structures greatly increase the area of the secreting and absorbing surface.

      The walls of the small intestine house numerous microscopic glands. Secretions from Brunner glands, in the submucosa of the duodenum, function principally to protect the intestinal walls from gastric juices. Lieberkühn glands, occupying the mucous membrane, secrete digestive enzymes, provide outlet ports for Brunner glands, and produce cells that replace surface-membrane cells shed from the tips of villi.

      Peristaltic waves move materials undergoing digestion through the small intestine, while churning movements called rhythmic segmentation mechanically break up these materials, mix them thoroughly with digestive enzymes from the pancreas, liver, and intestinal wall, and bring them in contact with the absorbing surface.

      Passage of food through the small intestine normally takes three to six hours. Such afflictions as inflammation ( enteritis), deformity (diverticulosis), and functional obstruction may impede passage.

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Universalium. 2010.

Look at other dictionaries:

  • Small intestine — Intestine In*tes tine, n.; pl. {Intestines}. [L. intestinum: cf. F. intestin. See {Intestine}, a.] [1913 Webster] 1. (Anat.) That part of the alimentary canal between the stomach and the anus. See Illust. of Digestive apparatus. [1913 Webster] 2 …   The Collaborative International Dictionary of English

  • small intestine — ► NOUN ▪ the part of the intestine that runs between the stomach and the large intestine …   English terms dictionary

  • small intestine — n. the narrow, convoluted section of the intestines, extending from the pyloric end of the stomach to the large intestine and including the duodenum, jejunum, and ileum: see INTESTINE …   English World dictionary

  • Small intestine — Infobox Anatomy Name = Small intestine Latin = intestinum tenue GraySubject = 248 GrayPage = 1168 Caption = Diagram showing the small intestine Caption2 = Precursor = System = Artery = Vein = Nerve = celiac ganglia, vagus… …   Wikipedia

  • Small intestine — The part of the digestive tract that extends from the stomach to the large intestine. * * * small intestine n the part of the intestine that lies between the stomach and colon, consists of duodenum, jejunum, and ileum, secretes digestive enzymes …   Medical dictionary

  • small intestine — UK / US noun [countable] Word forms small intestine : singular small intestine plural small intestines medical the tube in your body that food goes into after it has passed through your stomach …   English dictionary

  • small intestine — small in testine n the long tube that food goes through after it has gone through your stomach →↑large intestine …   Dictionary of contemporary English

  • small intestine — small′ intes′tine n. anat. intestine 2) • Etymology: 1760–70 …   From formal English to slang

  • small intestine — small in testine noun count the tube in your body that food goes into after it has passed through your stomach …   Usage of the words and phrases in modern English

  • small intestine — noun The upper part of the intestine, between the stomach and the large intestine, divided into the duodenum, the jejunum and the ileum. Syn: small bowel …   Wiktionary

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