For the normal functioning of the human body, food intake is necessary. The absorption of the substances necessary for life and the products of their cleavage is carried out precisely in the small intestine. The intestinal villi located in it also carry out this function. Their anatomy, placement, cytology will be discussed further.
The structure of the small intestine, its functions
In human anatomy, there are 3 sections - the duodenum, skinny and iliac. The first is about 30 cm long. Special enzymes from the intestinal epithelium, bile, and pancreatic enzymes come here. In the same section, the process of absorption begins. Water and salts, amino acids and vitamins, fatty acids are actively absorbed with the help of villi.
There is no clear external border between the lean and iliac, and the total length is 4.5-5.5 m. But internal differences, of course, exist. Jejunum :
- has a large wall thickness;
- her intestinal villi are longer and smaller in diameter, and their number is greater;
- it is better supplied with blood.
Still, the main function of the duodenum is the digestion of food. This process is carried out not only in the intestinal cavity, but also near the walls (parietal digestion), as well as inside the cells (intracellular).
For the implementation of the latter, there are special transport systems in the mucosa, specific for each ingredient. An additional function of this part of the small intestine is absorption. The rest is the main function.
Placement of villi and their anatomy
Intestinal villi in the digestive canal are located in all three sections of the small intestine and give them a velvety appearance. The length of each villus is approximately 1 mm, and the placement is very dense. They are formed from protrusions of the mucous membrane. On one square millimeter of the surface of the first and second sections of the small intestine, they can be from 22 to 40 pieces, on the ileum - up to 30.
Outside, all intestinal villi are covered with epithelium. Each of the cells has many outgrowths called microvilli. Their number can reach 4 thousand per epithelial cell, which significantly increases the surface of the epithelium, and, as a result, the intestinal absorption surface.
All intestinal villi in the human digestive canal have a lymphatic capillary along the axis , originating at the apex of the villi and many blood capillaries located in the stroma.
Cellular composition of the villi
It is the presence of a certain type of cell that is responsible for how the intestinal villus functions. But first things first:
Each villus, regardless of location, is lined with an epithelial layer consisting of 3 cell varieties: columnar epithelial cell, goblet exocrinocyte and endocrinocyte.
Enterocytes
This is the most common type of cell in the villus epithelium. Its second name is the columnar type epithelial cell. Prismatic cells. And the main function of intestinal villi is performed by them. Enterocytes provide movement from the gastrointestinal tract to the blood and lymph of the body's necessary substances, which come during eating.
Epithelial cells on the surface have a special border formed by microvilli. These microvilli per 1 ΞΌm 2 are from 60 to 90 pieces. They increase the suction surface of each cell by 30-40 times. Glycocalyx, located on the surface of microvilli, produces cleaving enzymes.
One of the varieties of epithelial cells are cells with micro folds or the so-called M-cells. Their location is the surface of the lymphatic follicles, both group and single. They are distinguished by a more flattened form and a small number of microvilli. But at the same time the surface is covered with micro folds, with the help of which the cell is able to capture macromolecules and intestinal lumen.
Goblet Exocrinocytes and Endocrinocytes
Single cells, the number of which increases from duodenum to iliac. These are typical mucous cells that accumulate and then secrete their secret to the surface of the mucous membrane. It is mucus that promotes the movement of food along the intestines and at the same time participates in the process of parietal digestion.
The appearance of the cell depends on the degree of accumulation of secretion in it, and the formation of mucus occurs in the area of ββthe Golgi apparatus. An empty cell that has completely secreted its secret is narrow and with a reduced nucleus.
It is endocrinocytes that synthesize and secrete biologically active substances, which not only play a digestive function, but also play an important role in general metabolism. The main location of these cells is the duodenum.
Functions
From the structure, it immediately becomes clear what function the intestinal villi perform in the digestive process, so we will only list them briefly:
- Absorption of carbohydrates, proteins, amino acids, as well as their decomposition products. They are transmitted through the villi to the capillaries and, together with the blood, are transferred to the portal system of the liver.
- Absorption of lipids, or rather, chylomicrons, particles derived from lipids. They are transmitted by villi into the lymphatic system and further into the circulatory system, bypassing the liver.
- Another function of intestinal villi is secretory, secretes mucus for easier movement of food through the intestines.
- Endocrine, because some cells of villi produce histamine and serotonin, secretin and many other hormones and biologically active substances.
Embryo bookmark and regeneration after damage
What cells are composed and how does the intestinal villi function, we figured out, but when is it laid in the human body and from which cells? We will deal with this issue.
At the end of the second month or the beginning of the third intrauterine development of a person, sections of the small intestine and its functional components - folds, villi, crypts begin to form from the intestinal endoderm.
At the beginning, epithelial cells do not have strict differentiation; only at the end of the third month do they separate. Glycocalyx on the microvilli with which epithelial cells are coated is laid in the fourth month of the baby's development.
In the fifth week, with the correct course of pregnancy, the serous membrane of the intestine is laid, and in the eighth - the muscular and connective tissue of the intestine. All shells are laid from the mesoderm (visceral leaf) and connective tissue mesenchyme.
Although all the cells and tissues of the digestive system are still in the fetal development, intestinal villi can be damaged during the performance of their functions. How is the restoration of the sites where the cells died? By mitotic division of healthy cells located nearby. They simply take the place of dead brothers and begin to fulfill their function.