Small intestine

The small intestine (intestinum tenue) follows the stomach Department of the digestive system length from 2.8 to 4 m, ends with ileocecal valve in the right iliac fossa. The corpse of the small intestine reaches a length of up to 8 M. the small intestine is divided without particularly clear boundaries into three sections: duodenal intestine (duodenum), skinny (jejunum), iliac (ileum).
According to its functional value of the small intestine is in the digestive system. In the lumen under the action of intestinal juice (volume 2 l), pancreatic juice (volume 1-2 l) and bile liver (volume 1 l) is the final breakdown of all the nutrients into its component parts: protein is broken down to amino acids, hydrocarbons - to glucose, fats - up of glycerin and soap. The products of digestion are absorbed into the blood and lymphatic vessels. Characteristic is that all split substances dissolve in water, forming isotonic solutions. Only in this manner possible resorption through the epithelium of the colon. In the thickness of the wall of the intestine, blood, lymph and liver, the synthesis of protein, fat and glycogen from the incoming nutrients.
All part of the small intestine have a common structure. The wall of the intestine consists of shells: the mucous membrane, submucosal basis, muscle and serous.
The mucous membrane (tunica mucosa) covered with a single layer of prismatic kamchatyi epithelium. Each cell on the side facing the cavity cancer, has up to 3,000 microvilli that in the light microscope have views edges. At the expense of microvilli suction surface of cells increases in 30 times. Along with prismatic cells are single goblet cells that produce mucus. Under the epithelium is a delicate tissue basal plate, separated from submucosal basis lamina muscularis. The surface of the mucous membrane contains a circular folds (plicae circulares), about 600, and 30 million villi (villi intestinales) height 0,3-1,2 mm is a Hair is a finger swelling of the mucous membrane (Fig. 238). In the hair are loose connective tissue of smooth muscle fibers, artery and vein. In the Central part lies blind growth of lymphatic capillary, called the milky sinus (Fig. 239). Between the fibers are visible deepening - crypt mucosa number about 150 million; the crypt arise spacelane basal membrane into the side of the duct intestinal glands (gll. intestinales). Thanks to the presence of microvilli, circular folds, lint and crypts absorption surface of the mucous membrane in comparison with smooth surface on the equivalent of a segment of bowel is increased in 1000 times. This fact is extremely important adaptive aspect that helped the development of a person relatively short bowel, but have time due to the large area of mucous membrane to rezervirovat almost all nutrients from the gastrointestinal tract.

histological structure of the villi
238. Histological structure of the fibers.
1 - epithelium; 2 - the milky sinus; 3 - crypt; 4 - gland; 5 - muscle layer of mucous membranes.

villi ileum scheme
239. Villi ileum (scheme) (R. D. Sinelnikov).
1 - artery (red); 2 - Vienna (blue); 3 - lymphatic capillaries (yellow).

Submucosal basis (tela submucosa) of almost the entire small intestine loose, highly mobile. In the submucosa of the duodenum occur limit departments gll. duodenales. Their secret is poured into the intestines. The secret glands crypt contains enterokinase, activating trypsinogen pancreatic juice. In the initial section of the duodenum are the glands that produce pepsin and dipeptidase for the breakdown of proteins. In the submucosa meets the accumulation of lymphatic tissue in the form of follicles.
Muscular layer (tunica muscularis) is composed of smooth muscles which form the inner circular and outer longitudinal layer. Their thickness is much less than in the wall of the stomach. Starting from duodenal towards the end of the small intestine muscular layer thickens. Circular fibers that make up the steep spiral, can reduce the intestinal lumen. Longitudinal muscle fibers cover intestine flat spiral with a turnover round of 20-30 cm, causing a shortening of the intestinal tube and the formation of a pendulum-like movements.
The serous membrane - peritoneum (tunica serosa), with the exception of the duodenum, covers the small intestine from all sides, forming the intestine mesentery. The peritoneum is covered by mesothelium and is the basis of connective tissue.