Tasks of the small intestine

Synonyms in a broader sense

Interstitium tenue, jejunum, ileum, duodenum

English: intestinal


The small intestine is used for digestion. The food pulp is broken down further so that the nutrients and water can be absorbed.

Functions of the small intestinal mucosa

The lining of the small intestine (Tunica mucosa) has a variety of tasks in the human body. For one, some of their cells produce roughly per day one liter of a bicarbonate-rich secretion. These are, for example, the so-called Brunner's glands of the duodenum (Duodenum) and the epithelial cells in the indentations (=Crypts).
The Mucinwhich are responsible for the slimy consistency of the secretion are produced by the goblet cells. Of the The slime film serves as a sliding layer for the food pulp (Chyme), which can thus be transported forwards better by the undulating small intestine. also the mucus protects the lining of the small intestine before the sour pH value the food pulp, which is mainly caused by stomach acid. The mucus also protects the mucous membrane of the small intestine from digestion by various enzymes.

The bicarbonate, as a base, ensures that the food pulp does not become too acidic. The secretion of bicarbonate is then also stimulated by a drop in the pH value, as well as by various hormones from the gastrointestinal tract.

Other tasks the lining of the small intestine are those Breakdown and absorption of food as well as the Water absorption.
In addition, especially in the duodenum (Duodenum) and jejunum (Jejunum) numerous Hormones which, among other things, regulate gastric acid secretion (= endocrine feedback mechanisms). These include secretin, GIP (gastrointestinal peptide), CCK (Cholecystokinin) and VIP (vasoactive peptide).

Illustration small intestine

Figure small intestine: location of the digestive organs in the body cavity (small intestine - red)
  1. Small intestine -
    Intestine tenue
  2. Duodenum, upper part -
    Duodenum, pars superior
  3. Duodenal
    Jejunum junction -
    Duodenojejunal flexure
  4. Jejunum (1.5 m) -
  5. Ileum (2.0 m) -
  6. End part of the ileum -
    Ileum, pars terminalis
  7. Colon -
    Intestinum crassum
  8. Rectum - Rectum
  9. Stomach - Guest
  10. Liver - Hepar
  11. Gallbladder -
    Vesica biliaris
  12. Spleen - Sink
  13. Esophagus -

You can find an overview of all Dr-Gumpert images at: medical illustrations

Functions of the small intestine villi

Through the Unfolding the small intestinal mucosa into large (Kerckring) Wrinkles (Plicae circulares), smaller villi (Villi intestinales) and the so-called brush border (Microvilli), is her Greatly enlarged surface. This is necessary especially for that Absorption of water. Of the 8 liters of fluid that enter the small intestine every day, about 6 liters are absorbed into the body. The rest of the way continues into the colon.

Together with the water become water-soluble vitamins such as vital minerals such as sodium, chloride, potassium, calcium, magnesium and phosphate.
In addition, there are numerous enzymes in the brush border that catalyze the breakdown of the various food components.

Functions of the small intestine sections

In the duodenum (Duodenum) and in the jejunum (Jejunum) finds the Bulk of carbohydrate digestion instead of. Enzymes in the brush border break down more complex carbohydrates, which are then converted into simple sugars (Monosaccharides) are absorbed into the small intestine cells via transporters.

Also the digestion of Fats (Lipids) and the absorption of lipid breakdown products take place here with the help of enzymes from the secretion of the pancreas (pancreas) instead of. Furthermore, in the duodenum (Duodenum) Iron is absorbed.

The digestion of Proteins also takes place mainly in the duodenum and jejunum. First columns certain enzymes (so-called Oligopeptidases) the proteins into their constituent parts, then these (smaller proteins or peptides and amino acids) are transferred to the cells of the mucous membrane (Enterocytes) recorded.

In the ileum (Ileum) takes place the absorption of vitamin C as well as from Vitamin B12 with the help of the so-called Intrinsic factorsthat is formed in the stomach instead. Vitamin B12 plays an important role in blood formation, which is why damage in the ileum is often associated with anemia (anemia) accompanied.

Egg white (proteins)

Since the pH value in the duodenum is almost neutral, the enzyme pepsin, which is active in the acidic gastric juice, can no longer continue Proteins digest and split. Thus, the protein digestion in the duodenum is stopped for the time being. Now the Pancreatic juice in the duodenum. The enzymes Trypsin and Chymotrypsin from the pancreatic juice are activated in the alkaline environment of the duodenum and continue protein digestion. The peptides (shredded proteins) produced by the cleavage are then again used by other enzymes (Peptidases), which are located on the microvilli of the small intestinal mucosa, are split into smaller peptides (di and tripeptides). These small protein units can then enter the superficial intestinal cells through various molecular uptake mechanisms (Enterocytes).


Different enzymes take part in the breakdown of the different sugars (carbohydrates) that people consume. Carbohydrate digestion begins in the oral cavity, where through Ptyalin (an a-amylase) the starch already in malt sugar (Maltose) and other polysaccharides (Oligisaccharides) will split. The enzymes are then used in the small intestine Lactase, Sucrase and Maltase the sugars are broken down into their components glucose, galactose, mannose and fructose. These sugar components are then transferred to the cells of the small intestine through various molecular mechanisms (Enterocytes) recorded.


Under the influence of the enzyme Lipase from the pancreas are the triglycerides (neutral fats) in glycerin and free fatty acids split. The bile acids contained in the liver are formed, these components are built into a structure that one Micelle is called. In the micelles, these fat-soluble substances can pass through the intestinal cells, where they are introduced into a protein-fat molecule (chylomicron).


The vitamins, which are fat-soluble, are transported through the intestinal wall together with other fats in the micelles mentioned above. The water-soluble vitamins passively diffuse through the intestinal wall. A special exception is vitamin B-12, which forms a complex with the intrinsic factor formed in the stomach and can only be absorbed in the ileum through this connection.

Functions of the wall of the small intestine

The muscle layer of the small intestine wall (Tunica muscularis) serves with its undulating contraction (peristalsis) the Transportation of the food pulp. This is also well mixed and crushed. The contractions are triggered by pacemaker cells, the so-called Cajal cells. These in turn are controlled by the enteric nervous system, the "nervous system of the intestine". It comprises two nerve plexuses, of which the Auerbach plexus is primarily responsible for blood flow and motility. This can be stimulated, among other things, by stretching the wall of the small intestine and triggering the contraction of the intestinal muscles near the mouth as well as the relaxation of the intestinal muscles far from the mouth, which causes the food to move towards the large intestine. This is also called the peristaltic reflex designated.