The epidermis , or skin (from the Greek. Ἐπί “on, with” + δέρμα “skin”), is the outer layer of the skin . It is a multilayer derivative of the epithelium .
In thick skin (not covered with hair), it includes five layers [1] located above the dermis and performing a predominantly barrier function.
In thin skin (covered with hair) there is no shiny and sharply thinned granular layer.
The epidermis is constantly updated. A similar effect is associated with specific transformations and the migration of keratinocytes from deep layers to the outer during their differentiation. Together with exfoliating scales, chemical and biological pathogens are removed from the skin surface. The epidermis presents some components of the immune system .
Content
The structure of the epidermis
Basal layer (sprout)
Due to the functionality of cell division, keratinocyte activity, the basal and spiky layers are combined in the Malpighi sprout layer . Normally, the epidermis regeneration process provides the basal layer, however, if damaged, the prickly layer can also take on a cambial function.
It is represented by basal keratinocytes associated with desmosomes . They are located directly on the basement membrane, to which are connected by semi-desmosomes. They are cylindrical in thin skin and oval in thick skin. They have a set of general purpose organelles, tonofilaments, tonofibrils that form the supporting network, as well as melanosomes . Melanosomes - granules of melanin that protect against the action of UV rays , keratinocytes are obtained from melanocytes.
Some basal keratinocytes are cambial cells. In addition to keratonocytes and melanocytes, there are other cells in the basal layer. These are Langerhans, Merkel , Greenstein cells, intraepidermal T-lymphocytes . Granulocytes and mast cells are very rare. The sprout layer includes the entire basal layer and part of the prickly.
Prickly layer
It is formed by prickly keratinocytes located in ten or more rows. Langerhans cells are found in the lower rows. Prickly keratinocytes have characteristic processes - "spikes", with the help of which they are connected with each other. In addition to general-purpose organelles, there are keratinosomes (Odland granules) - modified lysosomes surrounded by a membrane and a modified tonofibrillar apparatus that forms concentric condensations around the nucleus. Its function is the mechanical protection of the cell nucleus from damage.
Grain Layer
It has 1-2 rows of cells elongated parallel to the skin. The number of organelles decreases, the cytoplasm contains keratogialin granules associated with tonofibrils. There are also keratonosomes. The contents of these granules are released in the upper rows of the granular layer, where lamellar structures are formed from it. Such structures are hydrophobic and prevent the penetration of water into the underlying layers. Also, the synthesis of keratolinin and filagrin begins, due to which keratogialin is formed and further keratinization of the epithelium occurs.
Shiny layer or cyclic layer
With light microscopy, cells are not detected, and this layer looks like a shiny, homogeneous strip of pinkish color. It consists of 1-2 rows of flat cells with unexpressed borders, devoid of nuclei and organelles. It is well developed on the palms and soles.
Stratum corneum
The stratum corneum performs a protective function and has no living cells. The layer is formed by horny scales - dead keratinocytes connected by interdigitations of their cytolemma . The thickness of this layer directly depends on the intensity of the mechanical load. Normally, it is a good barrier to many pathogens .
Keratinization Process
Keratinization is a complex process that takes place in the cells of the epidermis and ends with the deposition of keratin (a protein substance) and fats in the stratum corneum, as a result of which the stratum corneum of the skin gains strength and elasticity. Keratin is formed from amino acids released during the degeneration of the cells of the spiky layer of the epidermis, fat - mainly from the keratogialin of the granular layer (see Skin). Violation of the keratinization process is observed with various dermatoses (see Daria's disease, Keratoses).
Additional Facts
There is also an abbreviation for Key Stanislav "Big Bison" for quick memorization of the histological structure of the epidermis:
- B - Basal layer;
- Ш - Prickly layer;
- Z - Grain layer;
- B - Shiny layer;
- P - Stratum corneum.
Gallery
Human epidermis and dermis
Cut epidermis
Optical tomography of the fingertip
Scheme of all levels of human skin
Notes
- ↑ Marks, James G. Lookingbill and Marks' Principles of Dermatology / James G Marks, Jeffery Miller. - 4th. - Elsevier, 2006. - P. 1–7. - ISBN 1-4160-3185-5 .
Literature
- Dogel A.S. Epidermis // Brockhaus and Efron Encyclopedic Dictionary : in 86 volumes (82 volumes and 4 additional). - SPb. , 1890-1907.
- Bykov V. L. Private histology of man. - SPb. : Sotis, 2001 .-- 304 p. - 3000 copies. - ISBN 5-85503-116-0 .