small intestine

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small intestine:

see intestineintestine,
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.
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.

Intestine, Small

 

the portion of the gut of vertebrate mammals, including man, that is situated between the stomach and the large intestine. The final digestion of food, the absorption of nutrients, and the movement of chyme occur in the small intestine.

In mammals, including man, the small intestine is divided into three sections: the duodenum, the jejunum, and the ileum. The length of the small intestine differs according to the nature of the digestive process: in man it is 6–7 m long, in cattle 27–49 m, in dogs 1.8–4.8 m, in cats 0.8–1.3 m, and in swine 16–21 m. In man the diameter of the small intestine is 48 mm in the initial section and 27 mm at the place where the ileum empties into the large intestine.

The walls of all sections of the small intestine are composed of mucous, submucous, and serous membranes and a muscular coat. Each section varies in the microscopic and submicroscopic characteristics of the intestinal wall, which reflect differences in function. The surface area of the small intestine’s mucous membrane is greatly increased by folds and protuberances: examples are the spiral valve in the mucous membrane of some fishes, and the villi, folds, and crypts in the small intestine of birds, mammals, and man.

Food is digested both in the intestinal cavity itself and by means of membrane-mediated (parietal) digestion. Cavitary digestion is achieved by the flow of pancreatic juice, bile, and intestinal juice into the lumen of the small intestine. During this process, supramolecular aggregates and the large molecules of proteins, carbohydrates, and fats in the food mass are hydrolyzed by the proteolytic, amylolytic, and lipolytic enzymes in the small intestine. The products of intermediate hydrolysis are adsorbed on the surface of the mucous membrane of the small intestine, where the final stages of hydrolysis and transition to absorption take place.

Parietal digestion is achieved by means of enzymes that are structurally bound to the cell membranes of the intestinal epithelium. The digestion and absorption of food in the small intestine are accompanied by contractions of the intestinal walls that mix and stir the chyme and propel it through the intestine.

IA. L. KARAGANOV

small intestine

[′smȯl in′tes·tən]
(anatomy)
The anterior portion of the intestine in humans and other mammals; it is divided into three parts, the duodenum, the jejunum, and the ileum.

small intestine

the longest part of the alimentary canal, consisting of the duodenum, jejunum, and ileum, in which digestion is completed
References in periodicals archive ?
Lactose by itself can't be absorbed in the human small intestine.
Lactase is found in the tips of the cells lining the small intestine, which are directly in contact with intestinal contents.
In a study published in the medical journal Gastroenterology, principal investigator John Wallace says the extent of the hard-to-detect damage caused to the small intestine has only recently been discovered through use of small video cameras swallowed like pills.
Some studies showed that starvation stress caused the increased expression of sodium glucose co-transporter 1 (SGLT1) and peptide transporter 1 (PepT1) mRNA in the small intestine of chickens and rats (Gal-Garber et al.
The small intestine is a snaking, narrow tube roughly 6 meters (20 feet) long.
Most nutrients are absorbed in the small intestines and go to the liver.
In the boy's small intestine, those grain components would trigger a chain of events that can cause bloating, diarrhea, and malnutrition.
Concentrations of eosinophils in the small intestines of the allergic mice were more than double that in the control mice.
The drugs had apparently eradicated the bacteria in the small intestines of 25 of the 47 people who came back for a second breath test.
However, FDA says that based on scientific information provided during the interim final rule's comment period, it is no longer necessary to designate the entire small intestine as a prohibited cattle material.

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