As epidermis (Greek epi "on ", "above"; derma "skin" ) refers to the epidermis in vertebrates. It forms the outermost layer of the skin the actual protective sheath against the environment.
From the inside out, a distinction is five epidermal layers: basal layer (stratum basale), prickle cell layer (stratum spinosum ), granular layer (stratum granulosum ), gloss layer (stratum lucidum ) and the horny layer (stratum corneum). The epidermis consists of 90 percent of the keratinocytes, which are held together by desmosomes. In the outer layers it consists of cornified squamous epithelial cells.
The stratum basale - the " basal layer " - serves as a single-layer innermost cell layer of the regeneration of the skin; here the cell division takes place. One daughter cell begins its migration to the surface, the other remains and is divided again. The nutrient supply is still relatively good, because the epidermis itself contains no blood vessels. The boundary to the underlying dermis As with all epithelia by a basement membrane, which is largely flat in the fields of skin in the groin skin but strong by papillae ( projections of the dermis ) is deformed, the density of the structure of the dermal ridges pretending.
Within the basal cell layer are special sensory cells for tactile stimuli, the Merkel cells. In addition, here are melanocytes, the pigment-producing cells.
In the referred to as " prickle cell layer " stratum spinosum, the cells are connected by desmosomes with Zytoplasmaausläufer. Here begins the designated as keratinization, cornification gradually. As the cells shrink at a histological processing, they have a spiky appearance in the preparation. In the stratum spinosum will also find defense cells of the lymphatic system, which are called Langerhans cells.
Stratum spinosum and stratum basale stratum are summarized as germinativum ( synonym: seed layer, regeneration layer) called.
With progressive keratinization begins in this " granule cell layer " already the degradation of the cells, they change gradually into lifeless corneocytes. The outer shape flattens gradually settled and the cell interior becomes more and more dominated by Keratingranula. The nucleus is not as clearly delineated as in the stratum spinosum.
Named as " gloss layer " stratum lucidum is a very uniform looking under the microscope cell layer, which occurs pronounced only on the ridged skin of the hands and feet. It has the task to be a barrier against all forms of intrusion into the skin. It consists mainly of an oily layer with lower refractive differences (hence it appears transparent). Here keratohyaline liquefy to a semi-liquid, fat and protein-rich, acidophilic substance, the Eleidin. In the fields of skin, the stratum lucidum is hardly trained and therefore to recognize corneum only as a thin strip andersfärbiger cell under the almost unstructured stratum. It is here the transition layer for strongly inhomogeneous granule cell layer.
The transition to the stratum corneum, the outermost layer of the epidermis takes place abruptly. The now fully keratinized corneocytes form now as " horn cells " the " stratum corneum ", which can be thick depending on the region 12-200 cell layers. The cells of epidermis are dead and no longer contains cell organelles. Lipids between the cells form a water-repellent protective layer together with the horny cells.
The stratum disjunctum is the top layer of the cornea; It has by the air inclusions to a different contrast than the underlying material. Here the horn cells detach from each other by dissolving the contacts between cells. Usually this process is invisible to the human eye. When disturbed coordination of exfoliation, the corneocytes solve in larger organizations. Aggregations from 500 cells are visible flakes of skin with the naked eye.