Composition of lipids and proteins present in epidermis
Answers
Corneocytes contain a protein envelope (cornified envelope proteins) underneath the plasma membrane, are filled with water-retaining keratin proteins, attached together through corneodesmosomes and surrounded in the extracellular space by stacked layers of lipids.
The major function of the epidermis is to provide a barrier to the movement of water and electrolytes. Without this permeability barrier life would not be possible. This point is clearly illustrated when severe disruptions of the permeability induced by cutaneous burns or premature birth lead to profound problems in fluid balance and abnormal electrolytes, which can result in death. This cutaneous permeability barrier resides in the extracellular domains of the stratum corneum and consists of lipid enriched lamellar membranes that contain predominantly ceramides, free fatty acids and cholesterol. The cells in the stratum corneum i.e. the corneocytes, are surrounded by a cornified lipid envelop that consists of omega acylceramides that are covalently bound to the proteins that comprise the cornified envelope. The cornified lipid envelope plays an important role in linking the lipid enriched lamellar membranes to the cornified envelope that provides a scaffold that is required for normal permeability barrier function. Thus, while all cells require lipids as both structural and signaling molecules, keratinocytes have an additional need for lipids to form the extracellular lipid membranes and the cornified lipid envelope to provide for a fully functional permeability barrier.