ABSTRACT
The differentiation process in which basal epidermal cells gradually mature and transform into stratum corneum cells is known as keratinization. In this process, which takes about 14 days, plump, cuboidal or spheroidal, hydrated, highly metabolically active cells gradually become tough, hardened, biochemically inactive, thin, shield-like structures that are programmed to desquamate off the skin surface (Fig. 16.1). This process is biochemically complex and it is not surprising that it is subject to genetically determined errors. During keratinization, a tough, chemically resistant, cross-linked protein band is laid down just inside the plasma membrane and the whole cell flattens to a thin disc (corneocyte, Fig. 16.2). The corneocyte’s water content is reduced from the usual 70 per cent to 30 per cent and most of the cellular organelles, including its nucleus, are eliminated. The keratinous tonofilaments become organized in bundles and are spatially orientated. A further characteristic feature of the normal stratum corneum is the presence of an intercellular cement material that contains non-polar lipid and glycoprotein.
