Synonyms in a broader sense
Interstitium tenue, jejunum, ileum, duodenum English : intestinal
Introduction
The small intestine is used for digestion. The food pulp is further broken down so that the nutrients and water can be absorbed.
Tasks of the small intestinal mucosa
The mucous membrane of the small intestine (tunica mucosa) has many different tasks in the human body. On the one hand, some of its cells produce about one liter of a bicarbonate-rich secretion per day. These are for example the so-called Brunner glands of the duodenum and the epithelial cells in the indentations (= crypts).
The mucins, which are responsible for the slimy consistency of the secretion, are produced by the goblet cells. The mucus film serves as a sliding layer for the food pulp (chyme), which can thus be better transported forward by the undulating small intestine. In addition, the mucus protects the mucous membrane of the small intestine from the acidic pH value of the food pulp, which is mainly caused by gastric acid.
The mucus also protects the mucous membrane of the small intestine against digestion by various enzymes. The bicarbonate, however, acts as a base to ensure that the food pulp does not become too acidic. In this way, the secretion of bicarbonate is also stimulated by a drop in the pH value, and also by various hormones from the gastrointestinal tract.
Other tasks of the mucous membrane of the small intestine are the splitting and resorption of food and the absorption of water. In addition, numerous hormones are produced, especially in the duodenum and jejunum, which regulate, among other things, the secretion of stomach acid (= endocrine feedback mechanisms). These include secretin, GIP (gastrointestinal peptide), CCK (cholecystokinin) and VIP (vasoactive peptide).
Tasks of the villi of the small intestine
Due to the unfolding of the mucous membrane of the small intestine into large (Kerckring) folds (Plicae circulares), smaller villi (Villi intestinales) and the so-called brush border (Mikrovilli), its surface is greatly enlarged. This is necessary especially for the absorption of water. Of the 8 liters of fluid that enter the small intestine daily, about 6 liters are absorbed into the body.
The rest continues to enter the large intestine. Together with the water, water-soluble vitamins and vital minerals such as sodium, chloride, potassium, calcium, magnesium and phosphate are absorbed. In addition, numerous enzymes are located in the brush border, which catalyse the splitting of the different food components.
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