ABSTRACT

Life in a terrestrial environment threatens mammals with desiccation, if transcutaneous water loss is unrestricted. In addition, the external skin layers must defend the organism from mechanical insults and pathogenic microbes, as well as from continuous bombardment by both UV-irradiation and free radicals generated from the ozone and other environmental pollutants. In addition, the barrier layers must also desquamate invisibly; trap appropriate amounts of water (hydration); metabolize exogenous xenobiotics; and even transduce sensory signals, i.e., they serve as a psychosensory interface. This volume devotes one or more chapters to most of these important protective (‘‘barrier’’) functions. Yet, it is the structural, biochemical, regulatory, and pathophysiologic mechanisms that sustain permeability barrier homeostasis, which are justifiably the major emphasis of this book. Unfortunately, other worthy ‘‘barrier’’ mechanisms, such as epidermal UV filtration by endogenous molecular filters, are not included, in part because of space considerations, and also because of a dearth of current research activity and interest. Perhaps future editions of this volume will do greater justice to this and other topics. In Chapter 2, we discuss how several of these protective functions are linked topographically, structurally, or biochemically, and how many of these functions are co-regulated.