The outer cover of the body has a rather complex structure. The skin is an organ that consists of two layers. It performs a number of important functions: metabolic, heat-regulating, receptor, protective. Many are interested in what the epidermis is, but they forget about the second component of the skin - the dermis.
The structure of the outer cover of the body
The skin consists of two layers - the epidermis and dermis. The upper epithelial layer is separated from the lower by an uneven wavy line. Its appearance is caused by the presence on the skin surface of special outgrowths - papillae. Its upper layer is a keratinized stratified squamous epithelium. There are no
blood vessels in it, and nutrition to it comes only from the dermis.
Having figured out what the epidermis is, finding out where it is located, many begin to become interested in its structure. It consists of cells of various shapes and structures. They reflect certain phases of their life. The thickness of the epidermis, depending on its location, can be from 0.07 mm to 1.4 mm. The thickest layer is on the soles of the feet, palms. And the thinnest skin (its upper layer) is located in the pubic region, on the forearms, auricles and abdomen.
The structure of the upper cornified cover
The epidermis consists of 5 separate layers. Its main component is called keratinocyte. But the structure of the epidermis is more complicated than it might seem at first glance. Specialists distinguish such layers:
- basal (germinal);
- prickly;
- grainy;
- brilliant;
- horny.
Each of them performs special functions and has its own structure.
It is important to know that epidermal cells are in a constant state of renewal. The layers undergo processes of reproduction, movement, keratinization and desquamation. Depending on the specific part of the body, the process of complete renewal of the epidermis can take from 20 to 30 days.
Stratum corneum
The upper part of the epidermis consists of cells that are tight enough to fit together. The components located in the stratum corneum are the epidermal skin barrier - they are called corneocytes. These epidermal cells have already lost cellular organelles and were filled with keratin.
Due to this, the keratinized components of the layer can protect the underlying tissues from mechanical damage, temperature fluctuations, drying out and penetration of bacteria. Horny scales are divided into two types. They may have loose or dense filling of keratin fibrils. On the surface are the second of them. And the first ones are located closer to the granular layer. In their structure, it is possible to detect residues from previously located cellular organelles in them. These flakes are often called T-shaped cells.
This upper layer of the epidermis is a skin barrier and consists of several layers of already dead cells that are impregnated with lipids. By the way, these substances are the main keepers of moisture in the skin.
Shiny layer
This part of the epidermis is not always expressed. It is also called the eleidine layer. If it can be detected, then it looks like a thin, bright, bright and uniform strip. The layer was named only due to its appearance. Its component is a substance called eleidine. It is the basis product for further keratinization of cells. They find it, as a rule, only in the skin of the soles and palms. It consists of nuclear-free flattened cells.
Granular layer
Those who figured out what the epidermis is, figured out where it is, and remember its thickness, understand that each of its components is negligible. So, the granular layer consists of only 1-2 rows of cells in those areas where the thin epidermis. But it can also consist of 10 rows of cells in those places where the skin is denser. They are diamond-shaped, elongated, elongated, and closely pressed together. The cells in this layer have already lost their ability to divide. In their cytoplasm there are two types of granules: lamellar and keratogialin. They are located so that the long axis of each rhomboid cell is parallel to the groove or scallop.
Prickly cells
Regardless of the location of the skin area, this layer consists of 5-10 rows. The cells found in it are in the form of polygons. When viewed under a microscope, you can see not only the layers of the epidermis of the skin, but also see the cells themselves, the narrow strips of space between them and the thin processes that intersect it. Due to their presence, the layer was called prickly.
Keratinocytes are connected in this part of the epidermis by desmosomes. They have a rather complicated structure: they look like 2 plates, and between them there are 4 electron-transparent and 3 electron-dense layers alternating between themselves. It is desmosomes that support the internal structure of cells, they are the guarantor of a strong intercellular connection. They also serve as attachment points for tonofilaments. It is worth noting that the human epidermis is designed so that in the upper areas of the prickly layer the number of desmosomes decreases.
The cell structure resembles the components of the basal section. But at the same time they are different. Prickly cells are interconnected by a significant number of desmosomes, and their tonofilament bundles are thicker.
Basal cells
This layer is the most distant from the surface of the skin. But it gives the full opportunity to understand what the epidermis is. The last layer is located on the basal plate, which limits it from other tissues. The cells in it are arranged in one row. The layer that they form is also called the germ layer. It contains several types of cells. There are keratinocytes, melanocytes, lymphocytes, tissue basophils. Greenstein and Merkel cells also enter the layer.
The keranocytes in this layer look like cylinders that are upright. They are distinguished by 2 types: with a flat and gear-like surface. The first of them are divided, due to them there is a change of cells. The second perform a backup function. But with any damage to the skin, they begin to actively share.
You can fully understand and understand how the structure of the epidermis is structured if you know that the structure of the components of the basophilic layer is slightly different. In addition to organelles and nuclei, which are characteristic of all other cells, they contain specific structures - tonophilamens. There are also special inclusions called melanin granules.
Separately, it is worth saying that melanocytes are special cells that can produce melanin. This substance protects against the damaging effects of ultraviolet radiation. In the basal layer is about 10-25% of these cells. In appearance, they resemble a sea urchin and are located between keratinocytes. In their long processes, they are able to transport melanin into the cells using phagocytosis.
Knowing all this information about the structure and features of the upper layer of the skin, one can imagine what the epidermis is, how it looks and what it is needed for.