Fig. 1

A schematic representation of the epidermis

The basal layer rests upon a basement membrane (BM) which is composed of extracellular matrix proteins and separates the epidermis from the dermis. Cell division takes place in the basal layer, and as cells leave this layer they undergo a progressive terminal differentiation culminating in enlarged, anucleate cells of the stratum corneum. The major intracellular proteins present in the keratinocytes of all layers are the keratins, which impart structural integrity. The hemi-desmosomes (HD) are structures responsible for connecting the basal cells to the anchoring filaments of the basement membrane, while desmosomes (D) provide cell-cell adhesion in suprabasal layers. Cells in the stratum corneum synthesize a structure termed the cornified envelope (CE) which acts primarily as a barrier to the external environment.