Anatomy and Pathophysiology

Most reviews of the anatomy and physiology of skin begin with detailed descriptions of cellular composition, structural proteins, and extracellular matrix (“ground substance”). Since each of these topics is presented in subsequent sections of this textbook, these aspects of cutaneous structure will be introduced only briefly with references to the appropriate chapters. Following this, the conventional approach is reversed by examining diseases that illustrate cutaneous function in the context of the cells and structures that sustain it. This method is derived from the assertion that the structure and function of the skin are best illustrated by disease. Thus, disease reveals function, and function illustrates structure. Cutaneous structures include an epidermis that serves as a barrier to prevent loss from within and damage from external insults and a dermis that provides mechanical support, circulation, and nutrition. Other functions provided by the cells in the skin include immune recognition and memory, the ability to repair damage, thermoregulation, and communication. Evidence that the skin has failed includes barrier disruption, infection, autoimmunity, cancer, and an undesirable appearance. These are the subjects of this introductory chapter. Ultimately, however, the most obvious function of the skin is to maintain an internal environment that allows an organism to protect its DNA and reproduce it reliably.