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1. The epidermis consists of five layers. The two most superficial layers (the stratum corneum and lucidum) contain nonviable keratinocytes.

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2. Collagen III provides tensile strength to the dermis and epidermis.

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3. Adult dermis contains a 4:1 ratio of type I:type III collagen.

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4. Of the congenital skin disorders, only pseudoxanthoma elasticum and cutis laxia are responsive to surgical rejuvenation.

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5. Hemangioma is the most common cutaneous lesion of infancy and a large majority spontaneously involute (resolve) past the first year of patient age.

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6. Basal cell carcinoma (BCC) is the most common form of skin cancer and nodular BCC is the most frequent form of this tumor.

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7. Breslow thickness is the most important prognostic variable predicting survival in those with cutaneous melanoma.

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As the largest human organ, the skin is one of the most complex and physiologically underappreciated elements of our bodies. Beneath its uniform appearance, the skin demonstrates profound regional variation due to the highly structured organization of many different cell types and dermal elements. Although primarily valued as a protective barrier allowing interface with our surroundings, the structure and physiology of the skin is complex and fascinating. As an environmental buffer, the skin protects against a vast array of destructive forces: The structural integrity of the epidermis creates a semipermeable barrier to chemical absorption, prevents fluid loss, protects against penetration of solar radiation, rebuffs infectious agents, and dermal durability resists physical forces. In addition, the skin’s ability to regulate body heat makes it the body’s primary thermoregulatory organ. The relative ease of analyzing skin specimens has made the skin one of the best-studied tissues of the human body. Not only does this fascinating organ form the primary focus of the subspecialties of plastic surgery and dermatology, but it also has driven research in a broad number of fields, including immunology, transplantation, and would healing.

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Anatomically, the skin may be divided into three layers: the epidermis, basement membrane, and dermis.1–3 With very little extracellular matrix (ECM), the epidermis is composed primarily of specialized cells that perform vital functions. Sandwiched between epidermal and dermal structures, the basement membrane anchors these layers together.1–3 This membrane fulfills many biologic functions, including tissue organization, growth factor reservoir, support of cell monolayers during tissue development, and semipermeable selective barrier. In addition to its role in providing soft-tissue durability, the dermis is primarily composed of a dense ECM that provides support for a complex network of nerves, vasculature, and adnexal structures.3,4 The ECM is a collection of fibrous proteins and associated glycoproteins embedded in a hydrated ground substance of glycosaminoglycans and proteoglycans. These distinct molecules are organized into a highly ordered network that is closely associated with the cells that produce them. In addition to providing the architectural framework that imparts mechanical support and viscoelasticity, the ECM can regulate the ...

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