What are the layers

The epidermis forms the interface between the human body and the environment. The epidermis is a classic proliferation tissue, i. H. it is subject to constant renewal.

The lowest layer of the epidermis is the basal cell layer (stratum basale = consists of one layer, the cells are cubic). This is where cells divide and regenerate cells. From here, the cells slowly migrate through further layers towards the surface of the skin. The transitions between the skin layers are fluid. The migration of cells from the basal cell layer to the surface takes about 28 days in healthy skin.

The first layer of cells that they reach is the prickly cell layer (stratum spinosum). Here (stratum spinosum = consists of many layers, the cells are spindle-shaped and flattened) the cells are connected with multiple “spike-like” intracellular bridges (desmosomes = tight rod-shaped connections, they are responsible for the mechanical stability of the skin). The appearance and connections of the cells give this layer its name. From here to the surface of the skin, the cells are surrounded by a “cell cement” or “cell mortar”, the extracellular lipid matrix. The extracellular lipid matrix consists mainly of lipids (fats) and proteins (proteins).

The next layer is the granule cell layer (Stratum granulosum = consists of one to several layers, the cells are clearly flattened). The granule cells contain hard protein bodies with a granular structure. In addition, “hard” fibrils develop (proteins = proteins - here collagen), which are responsible for the cross-linking of the keratin filaments. The cell nuclei degenerate and, together with the intracellular structures, are discharged into the extracellular matrix. This is where the conversion of living into dead keratinocytes (horn cells) takes place.

The outermost layer is the horny layer (stratum corneum = consists of approx. 120–150 layers, the cells are very flat). The lowest layer of this skin layer is the glossy layer (stratum lucidum) - it is characterized by a light-refracting effect. Here the cells are tightly packed. The layers are rich in fat and protein. In this way, they protect against water penetration and water loss from the depths (they contain: ceramides, cholesterol, cholesterol esters, fatty acids).