Skin Disorders Guide

The skin is an impressively large and heavy organ. It occupies well over a square meter of surface area and accounts for about 20% of total body weight. As the boundary between our body and a hostile world, it serves several functions. First, the skin acts as a barrier for fluid movement. Internal fluids are kept within the body, and external fluids are excluded from penetration. Second, the skin serves as the major means of temperature control for the body. Conservation of body heat occurs both through vasoconstriction and through the insulating properties of the skin itself. Cooling of the body occurs through vasodilation and the evaporation of sweat. Third, the skin offers important protection from ultraviolet light. Both melanin production by melanocytes and keratin production by keratinocytes serve to decrease the amount of damage done to cellular DNA as a result of ultraviolet light penetration. Fourth, the skin operates as the source of sensory input to the body. Sensory nerve endings that terminate at the junction of the epidermis and dermis carry important information to the brain regarding our external environment. Fifth, the skin is an organ of metabolism for some important molecules. This role is exemplified by the ability of epithelial cells to synthesize vitamin D.