Intestine is the longest part of the human digestive tract. There are: small intestine with 4-6.5 m length, in which occurs nutrients overgrazing and

Intestine structure and functions [Small, Large]

Intestine is the longest part of the human digestive tract. There are: small intestine with 4-6.5 m length, in which occurs nutrients overgrazing and absorption, and the large intestine with 1.1-2.1 m length.

The small intestine begins from the output of stomach with duodenum that has length of 18-22 cm. Liver and pancreas ducts flows in it (diagram 88). The enzymes of pancreatic juice cleave proteins (trypsin), fats (lipase) and carbohydrates (amylase, lactase). They are active only in alkaline medium and get activated by bile.

Bile is produced by the largest gland of the body — the liver. The composition of bile includes water, acid and bile pigment bilirubin. It accumulates in the gallbladder and excretes when bolus enters into the duodenum. The main function of bile — is emulsification of fat food. Fats may be digested by lipase only in the form of small droplets in an aqueous solution (emulsion). Bile enhances motor activity of the intestine, and performs the function of decontamination. Regulation of pancreatic juice and bile development is done by reflex (nerve) and humoral mechanisms. Predominant reflexes are the unconditioned ones.

Duodenum becomes thin, and further in the ileum. Almost the entire length of the small intestine has diameter of 3-5 cm. Its walls, as well as other parts of the digestive tract, are composed of four layers. The mucous membrane of the small intestine due to submucosal layer is collected in the folds — the intestinal villi. They multiply the digestive and the suction surface (diagram 89). Epithelial cells are covered with microvilli. Digestive enzymes, providing membrane digestion are placed in them with a certain sequence. Due to villae the suction surface of the small intestine reaches 450-550 m2 that is 300-380 times greater than the surface area of ​​the human body. There are many small glands that produce digestive juice in the mucous membrane of the small intestine. Under the influence of this juice finishes the cleavage of proteins into amino acids, fats into glycerol and fatty acids, carbohydrates into glucose.

The muscular layer of the intestinal wall allows mixing bolus due to the pendulum rate contractions and its movement as a result of peristaltic contractions.

The total duration of the food bolus movement and its digestion in the small intestine is 6-7 hours. Taken from http://worldofschool.org

Diagram 88. The liver, duodenum and pancreas: 1 — right lobe of the liver; 2 — left lobe of the liver; 3 — gall bladder; 4 — common hepatic duct; 5 — pancreatic duct; 6 — pancreas; 7 — the duodenum; 8 — duct of the gallbladder; 9 — common bile duct
Diagram 89. The villi of the small intestine: 1 — external (mucosa) shell; 2 — submucosa; 3 — muscular coat; 4 — serosa; 5 — lymphatic capillaries; 6 — arterial part of the capillary; 7 — venous part of the capillary; 8 — vein; 9 — artery; 10 — lymphatic vessel
Diagram 90. Nutrient digestion products suction by villi: 1 — protein; 2 — fats; 3 — carbohydrates; 4 — blood capillaries; 5 — lymphatic capillaries

In the small intestine villi absorb nutrients. In the center of each villi are lymphatic capillaries, and on both its sides — the small arteries and veins, which branch into capillaries (diagram 89). Smooth muscles located in the walls of the villi during digestion rhythmically reduce (5-6 times per minute), squeezing lymph from lymphatic capillary. Upon muscle relaxation there occurs a negative (relatively to gut cavity) pressure in the middle of the villi which sucks the water, minerals, salts, vitamins and nutrients into the villi (diagram 90).

Undigested remnants of food come from the small intestine into the large through peristalsis. The large intestine has: cecum with worm-like appendage (appendix), colon, sigmoid gut and rectum. E. coli is ​​constantly propagated in the appendix, it cleaves plant fibers, while synthesizing vitamin K and vitamins of group B. Water absorbs and stool forms in the large intestine, then they passes into the rectum. When inflammation of the appendix there is a disease that is accompanied by pain in the abdomen, fever, nausea and vomiting. If you have such symptoms you should call a doctor immediately.

Questions:
  • What parts does the intestine consist of?

  • Determine the relationship of the small intestine structure and functions.

  • Explain digestion mechanism in the duodenum.

  • Explain the importance of bile in the digestive process.

  • Explain the absorption mechanism of protein degradation products, fats and carbohydrates in the villi of the small intestine.

  • What is the relationship between the large intestine structure and functions?