Molecular structure of the epidermal extracellular spaces.

The skin is a protective cover that participates in the homeostatic regulation of internal fluids by preventing the passage of water, electrolytes and proteins into the external environment. The functional integrity of the skin is maintained through the interaction of the epidermis with the dermis. The epidermis is a tissue arranged in cellular layers. Those epidermal cells in direct opposition to the dermis are the basal cells. The epidermal basal cells are undifferentiated and endowed with mitotic activity. Obeying unknown stimuli, the basal cells undergo maturation following a differentiation pathway that ends with the formation of the stratum corneum. The stratum corneum is an inert film, made of fully differentiated epidermal cells. These cells are anucleated and contain tightly packed fibrous proteins embedded in an amorphous matrix and thick cell membranes. The structure of the epidermis allows a dynamic renewal of stratum corenum throughout life.