Keratinocyte
The keratinocyte ( synonym : the horny cell ) is the type of cell that occurs mainly (over 90 percent) in the epidermis . This cell type produces keratin and differentiates itself in the course of cornification , while it moves from the lowest layer of the epidermis to the uppermost layers (which face the outside world). The result is the corneocyte (synonym: the horny cell ).
Origin and development
Keratinocytes are derived from epidermal stem cells that are located in the area of the stratum basale or in the area of the outer root sheath of the hair follicle . As they are pushed up by the offspring cells, they wander through several stages of development until they form a layer of flattened, dead corneocytes in the stratum corneum .
The time between differentiation in the stratum basale and exfoliation as a corneocyte in the stratum disjunctum is about a month, but can be in certain diseases, e.g. B. in psoriasis , be shortened.
During this differentiation, the keratinocyte constantly changes its shape and geometric alignment. In the stratum basale , the keratinocytes arise from epidermal stem cells and have an approximately cylindrical shape. In the stratum spinosum , the remodeling of the cells begins with an increase in volume and a change in the cell axis in a more horizontal direction. There are keratohyalin formed and the conversion processes are progressing rapidly. The cells become flattened, the cell nucleus is lost , shrinkage due to fluid loss and finally cornification. Keratinocytes can no longer be detected in the following stratum corneum (horny layer). Keratinocytes became corneocytes.
tasks
The stratum corneum forms a barrier that keeps foreign bodies and germs out and protects the body from dehydration.
Keratinocytes are actively involved in the immune response, inflammatory processes and wound healing. They can produce a wide variety of cytokines , growth factors, and even complement factors . In many chronic inflammatory skin diseases, TNF-alpha and IL-1 in particular , but also many other interleukins and chemokines, are released.
Keratinocytes contribute to UV protection by taking up melanosomes (melanin-containing vesicles ) from melanocytes . The melanin is stored around the cell nucleus and protects it from UV-related damage.
Web links
- The life cycle of a horny cell In: Skin Care Forum Online ; Issue 35, October 2003