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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 appendix, 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 system.

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The middle portion of the small intestine, extending between the duodenum and the ileum.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


the part of the small intestine between the duodenum and the ileum
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
The effect of basil seed and AA supplementation on height, width, and crypt to depth ratio of duodenum, jejunum and ilium in heat stressed broiler chicken, is presented in Table IV.
In our present case, HP was located in the jejunal mesentery, although it was observed in contact with the jejunum wall, it and did not cause any clinical symptoms.
Mechanism by which glucose stimulates the passive absorption of small solutes by the human jejunum in vivo.
At surgery a tumour was found obstructing the distal jejunum. This was resected and an end-to-end anastomosis was performed.
In recent years, the jejunum has been transplanted using microvascular anastomosis, but death owing to total necrosis of the graft remains high (1).
The proximal stump of the jejunum is sewn to the distal jejunum to create a distal jejunojejunostomy.
Release of the mucosal mast cell granule chymase, rat mast cell protease II, during anaphylaxis is associated with the rapid development of paracellular permeability to macromolecules in rat jejunum. J Exp Med 182:1871-1881.
The other was an ulcerated, pedunculated polypoid mass (3 x 2.5 x 1.5 cm) located in the mucosa of the jejunum. In the partial hepatectomy, there were 3 well-defined nodules, which measured from 2 to 5 cm.
The small bowel or small intestine begins at the pylorus and consists of the duodenum, the jejunum and the ileum.
Enterostomies are created to establish an opening between the stomach or jejunum and the abdomen to provide nutrition to residents who are unable to swallow or tolerate oral feedings.|1~ Candidates for feeding tubes are often malnourished and frail, adding to their demands for care, and are at high risk for infection and skin breakdown.
The samples of small intestine tissues (approximately 3 cm from duodenum, jejunum and ileum, respectively) were collected on d 28 (2 pigs with average BW per pen) for the determination of small intestinal morphology and digestive enzyme activities.