REGIONAL VARIATION IN THE STRUCTURE AND PERMEABILITY OF ORAL-MUCOSA AND SKIN

Molecules of low to moderate size are capable of passage through the s kin and oral mucosa by simple diffusion. The diffusional resistance of the tissue is determined primarily by lipids in the intercellular spa ces of the outer layers of the epithelium. In the skin, palate, and gi ngiva, this barrier function is provided by a stratum corneum, the int ercellular spaces of which contain mainly ceramides, cholesterol and f atty acids. The more flexible regions of the oral mucosa are lined by a non-keratinizing epithelium, the outer half to one-third of which pr ovides a permeability barrier. The barrier region of the non-keratiniz ed epithelia contains phospholipids, cholesterol and monohexosylcerami des as major constituents. Differences in the composition and organiza tion of lipids in the epithelial barriers result in regional variation in permeability.