For the normal functioning of the human body, food is needed. The absorption of substances necessary for life and their breakdown products is carried out precisely in the small intestine. The intestinal villi located in it carry out this function. Their anatomy, placement, cytology will be discussed further.
The structure of the small intestine, its functions
In human anatomy, 3 sections are distinguished - duodenal, lean 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 absorption process begins. Water and s alts, amino acids and vitamins, fatty acids are actively sucked out 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, of course, there are internal differences. Jejunum:
- has a large wall thickness;
- her intestinal villi are longer and smaller in diameter, and their number is greater;
- she's bettersupplied 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, their own for each ingredient. An additional function of this section of the small intestine is absorption. In the rest, this is the main function.
Villus placement and 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 of the villi 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, there 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 absorption surface of the intestine.
All intestinal villi in the human alimentary canal have along their axis a lymphatic capillary originating at the top of the villi and many blood capillaries located in the stroma.
Cellular composition of villi
It is the presence of a certain type of cells that is responsible for how the intestinal villus functions. But first things first:
Each villus, regardless of location, is lined with a layer of epithelium, consisting of 3 cellular varieties: columnar epitheliocyte, goblet exocrinocyte and endocrinocyte.
Enterocytes
This is the most common cell type in the villus epithelium. Its second name is columnar type epitheliocyte. Prismatic cells. And the main function of the intestinal villi is performed by them. Enterocytes provide the movement from the gastrointestinal tract into the blood and lymph of the substances necessary for the body that come during meals.
Epithelial cells have a special border formed by microvilli on the surface. There are 60 to 90 of these microvilli per 1 micron2. They increase the suction surface of each cell by 30-40 times. Located on the surface of the microvilli, the glycocalyx produces degrading enzymes.
One of the varieties of epitheliocytes are cells with microfolds or the so-called M-cells. Their location is the surface of lymphatic follicles, both group and single. They are distinguished by a more flattened shape and a small number of microvilli. But at the same time, the surface is covered with microfolds, with the help of which the cell is able to capture macromolecules and the intestinal lumen.
Goblet exocrinocytes and endocrinocytes
Single cells,the number of which increases from duodenal to iliac. These are typical mucous cells that accumulate and then release 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 secretion accumulation in it, and the formation of mucus itself occurs in the area where the Golgi apparatus is located. An empty cell that has completely excreted its secret is narrow and with a reduced nucleus.
It is endocrinocytes that synthesize and secrete biologically active substances that not only play a digestive function, but also play an important role in overall metabolism. The main location of these cells is the duodenum.
Functions
From the structure it becomes immediately clear what function the intestinal villi perform in the digestive process, so we will only briefly list them:
- 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 transported to the portal system of the liver.
- Absorption of lipids, more specifically chylomicrons, particles derived from lipids. They are transmitted by villi to the lymphatic and then to the circulatory system, bypassing the liver.
- Another function of the intestinal villi is secretory, secreting mucus to facilitate the movement of food through the intestines.
- Endocrine, because some cells of the villi producehistamine and serotonin, secretin and many other hormones and biologically active substances.
Embryo formation and regeneration after injury
What cells does the intestinal villus consist of and how does it function, we figured it out, but when does it form in the human body and from which cells? Let's look into this matter.
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.
In the beginning, epithelial cells do not have strict differentiation, only by the end of the third month do they separate. The glycocalyx on the microvilli that cover the epithelial cells is laid down in the fourth month of the baby's development.
On the fifth week, with the correct course of pregnancy, the laying of the serous membrane of the intestine occurs, and on the eighth - the muscular and connective tissue membrane of the intestine. All shells are laid from the mesoderm (visceral layer) and connective tissue mesenchyme.
Although all the cells and tissues of the digestive system are laid down in fetal development, the intestinal villi can be damaged during the performance of their functions. How does the restoration of areas where cells die occur? By mitotic division of he althy cells located nearby. They simply take the place of their dead brothers and begin to fulfill their function.
