intestine

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intestine,

muscular hoselike portion of the gastrointestinal tract extending from the lower end of the stomach (pylorus) to the anal opening. In humans this fairly narrow (about 1 in./2.5 cm) tubelike structure winds compactly back and forth within the abdominal cavity for about 23 ft (7 m), and is known as the small intestine. It is not only an organ of digestion (for that part of the process not completed by the stomach) but is the chief organ of absorption. By contraction of its muscular walls (peristalsis) the food mass is propelled onward and, as it is carried along, it is subject to the digestive action of the secretions of the intestinal lining as well as to that of bile and pancreatic juice which enter the upper intestine (duodenum) from ducts leading from the liver and pancreas. Innumerable minute projections (villi) in the intestinal mucous lining absorb the altered food for distribution by the blood and lymphatic systems to the rest of the body. Food continues to pass into the middle (jejunum) and end (ileum) of the small intestines.

The small intestine joins the large intestine, or colon, at the cecum in the right lower abdominal cavity. Here, also, is the appendixappendix,
small, worm-shaped blind tube, about 3 in. (7.6 cm) long and 1-4 in. to 1 in. (.64–2.54 cm) thick, projecting from the cecum (part of the large intestine) on the right side of the lower abdominal cavity.
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, a blind pouch projecting from the cecum. The large intestine is wider in diameter. Its direction as it leaves the cecum is upward (ascending colon), across the abdominal cavity (transverse colon) beneath the stomach, and then downward (descending colon) on the left side of the abdominal cavity, making a sharp turn in the left lower portion (sigmoid) to merge with the rectum. In all, the large intestine is about 5 ft (1.5 m) long. Bacteria, the indigestible residue of food, and mucus form the bulk of matter in the large intestine. The water content of the bulk is absorbed through the walls of the large intestine, and the solid matter is excreted through the rectum.

See digestive systemdigestive system,
in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex.
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Intestine

The tubular portion of the digestive tract, usually between the stomach and the cloaca or anus. The detailed functions vary with the region, but are primarily digestion and absorption of food.

The structure of the intestine varies greatly in different vertebrates, but there are several common modifications, mainly associated with increasing the internal surface area. One, seen in many fishes, is the development of a spiral valve; this turns the intestine into a structure resembling a spiral staircase. Another, seen in some fish and most tetrapods, is simply elongating and then coiling the intestine. This can reach extremes in large herbivores: Oxen have intestinal lengths of over 150 ft (45 m). In numerous forms there are blind pouches, or ceca, off part of the intestine. In fish these are commonly at the anterior end; in tetrapods they generally lie at the junction between the large and small intestines. In all vertebrates the inner surface of the intestine is irregular, with ridges and projections of various sorts; these reach their maximum development in the extremely fine and numerous finger-shaped villi found in mammals.

In humans the intestine consists of the small and large intestines. The small intestine is further divided into three major parts: the duodenum, the jejunum, and the ileum. The duodenum, 10–12 in. (25–30 cm) long, begins at the pyloric sphincter of the stomach and curves around the head of the pancreas on the right side of the anterior part of the abdomen. It receives the ducts of the biliary system and the pancreas. The jejunum and ileum are about 19 ft (6 m) long and form a much-coiled tube that empties at right angles into the large intestine through the ileocolic valve (see illustration). The large intestine, or colon, consists of five parts: the ascending, transverse, descending, and sigmoid regions, and the terminal rectum which empties into the anal canal.

Junction of ileum with large intestine in humansenlarge picture
Junction of ileum with large intestine in humans

The microscopic structure of the intestine comprises an inner glandular mucosa, a muscular coat, and an outer serosa of connective tissues which is covered in most areas by peritoneum.

The intestine is supported by dorsal mesenteries of varying extent, which contain an extensive system of arteries, veins, lymphatics, and nerves to the various regions. See Digestive system

intestine

[in′tes·tən]
(anatomy)
The tubular portion of the vertebrate digestive tract, usually between the stomach and the cloaca or anus.

intestine

the part of the alimentary canal between the stomach and the anus
References in periodicals archive ?
A couple of months later, Frank had to have an operation to remove part of his pancreas, liver and lower intestine but he was given an good prognosis because he was still relatively young.
They pass, undigested, from the lower intestine to the colon, where beneficial bacteria consume them, releasing vitamins, minerals, and nutrients.
Last spring, he discovered obstetric fistula in Africa--the tear between the birth canal and the lower intestine that can happen during protracted labor and that, unless corrected, condemns a woman to a lifetime of physical misery and social ostracism.
The pin-worm, found mostly in children, lives in the lower intestine and rectum.
New evidence found in the boy's lower intestine was identified as being the highly poisonous calabar bean which police believe may have been used to subdue Adam before his death.
As you may know, prebiotics are complex carbohydrates, such as inulin and short-chain sugars and oligosaccharides, that pass undigested from the lower intestine to the colon.
In most people, the protein molecules probably work their way down to the lower intestine, where they are eaten by microorganisms.
The culprit turned out to be a virulent strain of Escherichia coli, normally a helpful resident of the lower intestine (SN: 7/22/00, p.
Group B Streptococcus (GBS) is a type of bacterium that is found in the lower intestine and/or vagina of 10-35% of healthy adults.
The cellulose compacts in the lower intestine and bacteria produce toxins which cause the weakened rodent to die of blood poisoning, so runs the theory.