Epidermal cells . Cells that make up the outermost layer of the skin .
Summary
[ hide ]
- 1 Epidermis
- 2 Main characteristics of cell types
- 1 Keratinocyte
- 2 Melanocyte
- 3 Langerhans cell
- 4 Merkel cells
- 5 inflammatory cells
- 3 Bibliographic references
- 4 Sources
Epidermis
The epidermis is made up of various types of epithelial cells : keratinocytes, melanocytes, Langerhans cells, Merkel cells, and inflammatory cells.
Main characteristics of cell types
Keratinocyte
Keratinocytes are the predominant cells (80% -90%) of the epidermis, the most superficial layer of the skin. They contain a very hard protein called keratin , which stimulates the growth of epithelial cells in the skin and of those that line the surface of the mouth , stomach and intestines . These cells originate in the basal epidermal layer and migrate to the stratum corneum, the outermost part, where they flatten out, losing their nuclei. The two main functions of keratinocytes are:
- Produce keratin, the main structural protein of the epidermis.
- They participate in the water barrier in the epidermis.
The epidermis is divided into layers according to the morphology of the keratinocytes (from the inside to the outside):
- Germination, regeneration or basal layer:
It is the deepest and is made up of a single layer of cuboidal cells that are arranged above the dermo-epidermal junction. In the basal layer, keratinocytes express K5 and K14 keratins.
- Thorny or Malphigian Cloak:
It is made up of multiple rows of keratinocytes expressing the K1 and K10 keratins of the eosinophilic cytoplasm, flattened and joined together by desmosomes.
- Grainy layer:
It consists of one or more rows of cells that contain K2 and K11 keratin granules. In certain locations, such as the palms of the hands and the soles of the feet, there is a visible, amorphous layer between the granular layer and the horny layer called lucid layer.
- Horny layer:
Cells that have lost the nucleus and make up the soft keratin. Keratinocytes are in continuous renewal and progressively pass from the basal layer to the upper zones, by cellular differentiation, to the horny layer, where they form a layer of dead cells in the form of scales and rich in keratin. It is estimated that it takes a month on the way from the basal layer (germ layer) to the horny layer, although the process may be accelerated in cases of hyperproliferation of keratinocytes (psoriasis). This layer constitutes a protective barrier against all kinds of harmful agents and pathogenic microorganisms . Keratinocytes migrate with a rocking motion during the wound healing process.
Melanocyte
Melanocyte is a dendritic cell that is derived from the neural crest and that migrates to the epidermis and hair follicle during embryogenesis . Its main function is the production of melanin, which is important in protecting against sunlight. In normal situations melanocytes are arranged at the level of the epidermal basal layer and contact the keratinocytes through their dendrites , there is one melanocyte for every 4 or 10 keratinocytes. The color of the skin depends on the melanocytes, depending on their activity.
The density of melanocytes is variable depending on the anatomical region, but it is very constant among individuals of different ethnicities. Epidermal melanocytes produce and secrete the pigment called melanin, which protects the body from the deleterious effects of non-ionizing UV radiation. The color of the skin depends on the activity of these cells. Melanin can be eumelanin (brownish-brown color) or pheomelanin (yellowish-red pigment). Both forms are produced from the oxidation of tyrosine to 3,4-dihydroxyphenylalanine (DOPA) through the action of the enzyme tyrosinase and the subsequent conversion of DOPA. These reactions initially occur in structures called premelanosomes, which derive from the Golgi apparatus. As more melanin is produced by oxidation of tyrosine, the internal structure of the premelanosome is transformed into the mature melanic granule (melanosoma). Developing melanosomes and their melanin content are transferred to neighboring keratinocytes by pigmentary donation. This process, which involves phagocytosis of the end of the melanocyte extension by the keratinocyte, is a type of cytocrine secretion (because a small amount of cytoplasm is also phagocytosed around the melanosome).
Melanocytes are related to some diseases such as vitiligo or melanoma . Vitiligo is characterized by the formation of white spots on the skin as a result of the lack of pigmentation of the skin. It is not well known why the process occurs, but some of the hypotheses involve the destruction of the melanocytes by the immune system itself, or by abnormal functioning of some nerve cells that will produce toxic substances causing damage to them. Melanoma is a type of skin cancer. It is formed by a concentration of malignant melanocytes. When the concentration is benign melanocytes, freckles, moles and lentigines appear.
Langerhans cell
Not to be confused with Langerhans islets or Langhans giant cell. Langerhans cells are abundant dendritic cells in the epidermis, containing large granules called Birbeck granules. They are normally found in the lymph nodes, but in histiocytosis they can be found in other organs. They derive from the bone marrow and usually reside in the stratified squamous epithelia. In the skin, they are commonly located suprabasally and make up about 3 to 4 percent of epidermal cells. First described by the then medical student Paul Langerhans in 1868, these cells were considered part of the nervous system. They were later classified as large macrophages. It is currently known to be the only epidermal cell that possesses surface markers characteristic of immunocompetent cells. These cells are part of the antigen presenting cells. They are found in the spinous layer of the stratified epithelium.
Merkel cells
Merkel cells are skin cells located in the basal layer of the epidermis. They can be found in isolation, in accumulations and in structures called tactile domes. The functions of Merkel cells have to do with mechanosensation, and with neuroendocrine secretion. The cell interacts with dendrites that are in close contact …… Embryologically, Merkel cells derive from the neural crest, reaching the palmar and plantar epidermis approximately between 8 and 12 weeks of gestation.
Inflammatory cells
The inflammatory response (inflammation) occurs when tissues are injured by bacteria, trauma, toxins, heat, or any other cause. Damaged tissue releases chemicals, including histamine, bradykinin, and prostaglandins. These chemicals cause blood vessels to leak fluid into tissues, causing inflammation. This helps to isolate the foreign substance from subsequent contact with body tissues. The chemicals also attract white blood cells called phagocytes that “eat” microorganisms and dead or damaged cells. This process is called phagocytosis. Phagocytes eventually die. Pus is formed due to the accumulation of dead tissue, dead bacteria, and live and dead phagocytes. These are some cells that help in this process:
- Lymphocytes
- Plasma cells
- Eosinophils
- Mast cells
- Neutrophils
- Epithelial cells
- Platelets
