The epidermis is the most superficial layer of the skin, in contact with the environment. It is formed by stratified pavement and keratinized epithelial tissue.
Its name derives from the greek words epi, which means above and dermis, which means skin. So it means above the skin.
It is about 0.03 to 0.05 millimeters on the palms of the hands and 2 to 4 millimeters on the soles of the feet.
The functions of the epidermis are:
- Serve as a protective barrier for the body;
- Absorption of ultraviolet rays from solar radiation;
- Prevent water loss;
- Promote the sense of touch.
cells
The cells of the epidermis are closely united and there is no kind of intercellular substance between them. There are four types of cells in the epidermis:
- keratinocytes: Present in greater numbers (95%), they are responsible for the production of keratin.
- Melanocytes: Responsible for the production of melanin, the pigment that gives skin color.
- Merkel Cells: Responsible for the sensation of touch, they are located in the deep region of the epidermis.
- Langerhans Cells: They are found in all layers of the epidermis, participate in the protection of the skin, as they have the ability to phagocytosis and activate T lymphocytes. We can say they are defense cells.
Layers
The epidermis is made up of five layers. Are they:
stratum corneum
The stratum corneum is the outermost layer of the epidermis, being formed by dead cells, with no nuclei and flattened. The cells have a lot of keratin and are continually shedding.
lucid stratum
The lucid layer is more evident in thick skin (palms of the hands and on the soles of the feet), whereas in regions of the body where the skin is very thin it is not possible to notice its presence.
It consists of a layer of flat, eosinophilic, translucent cells. In these cells it is not possible to see the organelles and the nucleus, which were digested by the enzymes of the lysosomes.
granular stratum
The stratum granulosum is formed by 3 to 5 layers of flat polygonal cells, with a central nucleus and accumulated cytoplasm of basophil granules (keratin-hyaline granules), which will give rise to keratin.
There are also lamellar granules, surrounded by membrane, which fuse with the cytoplasm of cells and release their lipid content into the intracellular space, forming a protective barrier that prevents the loss of Water.
thorny stratum
The stratum spinosum consists of 5 to 10 layers of cuboid cells, slightly flattened and with a central nucleus. A differential is that the cells present cytoplasmic projections with keratin filaments (tonofilaments), which keep the cells together, due to the presence of desmosomes. This entire arrangement gives this stratum a thorny appearance.
There are also stem cells of keratinocytes that began their formation in the germinal stratum.
germinal or basal stratum
The germinal stratum is the deepest layer of the epidermis and in contact with the dermis.
This layer is responsible for the renewal of the epidermis, showing intense mitotic activity. The produced keratinocytes are constantly pushed to the upper layers and increase their production of keratin. It takes up to 26 days for a basal cell to reach the stratum corneum, when it has reached its maturation.
Dermis and epidermis
Remember that the skin is made up of two layers: the epidermis and the dermis. THE dermis it is located just below the epidermis, being responsible for supporting and nourishing the most superficial layer of the skin.
The dermis is formed by dense connective tissue, made up of collagen, glycoproteins and fibers from the elastic system. It is also formed by two layers: papillary and reticular.
Read too:
- Human skin
- Skin layers
- hypodermis
- Integumentary System
- epithelial tissue
vegetable epidermis
The epidermis also covers the body of plants, that is, it is a tissue covering leaves, roots and stems. It is made up of a layer of intimately bonded, chlorophylled living cells.
It may also present some types of attachments, such as: stomata, hydatodes, trichomes, absorbent hairs and aculeum.
