ABSTRACT
Epidermal differentiation leads to the formation of the stratum corneum (SC), a heterogeneous tissue composed of lipid-depleted corneocytes embedded in a lipidenriched extracellular matrix, which subserves the barrier (Fig. 1). These lipids derive from a highly active lipid-synthetic factory (1), operative in all of the nucleated cell layers of epidermis, which generates a unique lipid-and hydrolase-enriched secretory organelle, the epidermal lamellar body (LB) (2,3) (Chap. 16). LBs are 0.3-0.4 0.25mm structures, which comprise about 10% of the cytosol of the stratum granulosum (SG) (2-4). Following secretion at the SG-SC interface, LB contents are processed from a polar lipid mixture into a hydrophobic mixture of ceramides, free fatty acids (FFAs), and cholesterol, and organized into the extracellular, lamellar membrane structures that form the hydrophobic matrix ‘‘mortar’’ within which corneocytes (‘‘bricks’’) are embedded (Fig. 1) (4).
