Functional Tasks

As a part of the digestive tract, the main function of the small intestine is to process the food and absorb the nutrients, electrolytes, vitamins and fluids it contains. In the small intestine, the previously chopped up food components are broken down into their basic components and absorbed. This is done on the one hand by adding digestive enzymes to the chyme and on the other hand by contact of the basic components with the cells of the small intestinal mucosa.

In order to make the contact surface of the chyme with the mucosa and thus the absorption of the food as large as possible, the small intestine uses several tricks here: Wrinkled protuberances protrude into the interior of the intestinal sections, from which cell clusters such as tentacles protrude once again. Each individual cell of these tentacles has so-called microvilli on its surface, finger-like protuberances that increase the contact area even more. In total, the small intestine thus increases its surface area to up to 200 m2.

When the chyme enters the duodenum through the stomach passage, the secretions from the gallbladder and pancreas (pancreas) empty out in its so-called “descending part”. The pancreas produces up to 1.5l of secretion daily. This consists mainly of bicarbonate, which neutralizes the acidic milieu of the rice.

The main work here, however, is done by the pancreatic enzymes, which are also contained in the pancreas, they further break down the food.There is a specific enzyme for each food component: for fats (including pancreatic lipase and phospholipase A), carbohydrates (alpha-amylase), proteins (including trypsin and aminopeptidases), DNA components (ribonuclease, deoxyribonuclease) etc. The part of the bile that is important for digestion is the bile acids, which have a special property. They can bind both fat and water and thus facilitate the processing of fats in food.

The bile acids, which are synthesized from cholesterol, form so-called micelles with the dietary fats. These are small “lumps” of fat, consisting of the fat components inside and the bile acids as a protective ring to the aqueous external environment. The mixture of chyme and digestive enzymes is now transported further towards the large intestine through the peristalsis of the small intestine.

The walls of the small intestine sections contract the slower the further they move away from the stomach. The duodenum contracts 12 times per minute, while the ileum has only 8 contractions per minute. However, the small intestine sections differ not only in the number of contractions per minute, but especially in their wall structure and the resorbed food components.

In the duodenum, mainly calcium, iron, magnesium, mono- and disaccharides are absorbed. In the further course of the process, fat-soluble vitamins, proteins, water-soluble vitamins and fats are now absorbed in descending order, until in the terminal ileum it is primarily the bile acids that are ultimately reabsorbed and vitamin B12 is absorbed. The further towards the large intestine one moves, the more accumulations of lymph follicles are also found in the intestinal wall.

Here, the intestine serves not only as a digestive organ, but also as a station of immune defense against germs and bacteria ingested with food. The final part of the small intestine is the Bauhin ́sche valve. It defines the transition from the small to the large intestine and prevents the backflow of stool from the large to the small intestine. Starting with the Bauhin ́schen valve, the number of intestinal bacteria increases rapidly and the species present change.