Enterocytes are cells of the intestinal mucosa. They perform numerous functions in digestion and also play a role in immune defense.
What are enterocytes?
The name enterocyte comes from the Greek. In German, the enterocyte is also called a hem cell. This type of cell is the most common type of cell in the small intestine. There, it is responsible for the absorption of various substances and materials from food. However, enterocytes are also found in reduced numbers in the large intestine. The intestinal cells obtain their energy from butyrate, which is produced by probiotics.
Function, effect, and tasks
The small intestinal cells perform many different functions. One of their main tasks is the absorption of small-molecule components of food. These include sugars, fats, fatty acids, amino acids, and vitamins. They are also involved in the active ion transport of sodium, potassium, calcium, magnesium and iron, for example. Via the enterocytes, these food components first reach the mucosa cells of the intestine and from there into the blood of the portal vein. This transports the nutrient components to the liver. Fats, on the other hand, are transported directly from the mucosa cells to the lymph. The transport of substances in the intestine can be active or passive. In passive absorption, nutrients move by osmosis from the site of high concentration to the site of low concentration. If there is no concentration gradient or if a substance is to be transported against the concentration gradient, active absorption is necessary. For this active resorption, enterocytes have numerous membrane proteins. These can then transport substances by consuming ATP. However, the enterocytes also serve to absorb water in the small intestine. In the small intestine, about 80 percent of the water is removed from the food pulp. A large part of the liquid comes from the digestive juices from the stomach and pancreas. In this way, around seven liters of fluid are recovered per day in the small intestine and large intestine. Furthermore, the enterocytes are part of the enterohepatic circulation. The enterohepatic circulation serves to recover bile acids. These are produced by the liver and play an important role in fat digestion. In the small intestine, the bile acids are reabsorbed by the enterocytes and transported to the liver via the portal vein. Here, the bile acids are then “recycled.” Enterocytes also play an important role in immune defense. They produce immunoglobulins. Immunoglobulins are antibodies. In particular, type A immunoglobulins (IgA) are produced in enterocytes. IgA develop their immune function primarily in secretions such as saliva, breast milk, in the intestinal secretion or also in the urogenital secretion. There, they serve as a defense against pathogens.
Formation, occurrence, properties, and optimal levels
Enterocytes are found predominantly in the small intestine. The intestinal mucosa of the small intestine consists of three layers. Inside the intestine is a blanket of single-layered cylindrical epithelium. This part of the intestinal mucosa is also called the lamina epithelialis mucosae. This is followed by a very thin layer of connective tissue (lamina propria mucosae) and a fine layer of muscle. This is also called the lamina muscularis mucosae. However, the intestinal mucosa does not line the intestine smoothly, but is folded to increase the surface area. Mucosa and submucosa form folds up to one centimeter high. These are called Kerck’s ring folds. However, not only the Kerck ring folds, but also the villi and microvilli of the intestinal mucosa contribute to surface enlargement. Microvilli are small protrusions of the cell membrane of the enterocytes. The enterocytes closely line the lumen of the intestine. The intestinal cells are connected to each other by so-called tight junctions. This tight cementation of the enterocytes serves as an intestinal barrier. In addition, they are surrounded by a 500nm thick glycoprotein structure. This is known as the glycocalyx. The membrane of enterocytes contains proteins that are required for the active transport of food components. Enterocytes feed to a large extent on butyrate. This is produced by probiotics in the intestine. A high-fiber diet serves as a nutrient for the good intestinal bacteria. Thus, such a diet indirectly has a positive effect on enterocytes.
Diseases and disorders
As mentioned earlier, enterocytes sit very close to each other due to tight junctions, thus serving as an intestinal barrier.However, various disruptive factors can impair the tight junctions, making the intestinal epithelium permeable to allergens, pathogens and harmful substances. Such disruptive factors include stress, alcohol, drugs or bacterial toxins. Various symptoms can result from the transfer of harmful substances and pathogens from the intestinal lumen into the bloodstream. The clinical picture is called leaky gut syndrome. Gaps in the barrier allow uncontrolled entry of antigens into the intestinal mucosa. As a result, numerous immune processes are set in motion. The increased antibody formation can lead to sensitization to food components. In addition, inflammatory mediators cause further damage to the intestinal mucosa. This starts a real vicious circle. The consequences of leaky gut syndrome are inflammation of the intestine, poor absorption of nutrients or autoimmune reactions. Enteritis also affects the enterocytes. Enteritis is an inflammatory disease of the small intestine. About one third of all infectious intestinal diseases are caused by viruses such as rotaviruses or noroviruses. However, bacteria or fungi can also cause enteritis. The pathogens penetrate the intestinal mucosa via the enterocytes and cause an inflammatory reaction there. In the process, a large number of enterocytes are destroyed by the defense cells. Typical symptoms of such an infection are diarrhea in combination with nausea and vomiting. Intestinal cramps or even fever may also occur. As a rule, most infectious intestinal diseases heal without complications after a few days.
