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Publisher Summary This chapter describes the physiology of the skin. The skin, which is the body's largest organ, contains the most extensive vascular supply. It maintains body temperature by regulating heat loss, prevents external organisms such as bacteria, fungi, and viruses from entering the body, protects it against environmental insults such as ultraviolet radiation, and relays diverse information to the central nervous system. The skin has three distinct anatomic compartments: (1) epidermis, (2) dermis, and (3) subcutaneous tissue. The epidermis has an outer inert keratin layer above a 5- to 10-cell thickness of keratinocytes. The epidermal compartment is highly cellular and approximately as thick as a sheet of paper. The epidermis consists of multiple layers of ectodermal cells called keratinocytes because of their abundant production of the tonofilament keratin. In addition to keratinocytes made from progenitor cells in the skin, the epidermis normally has immigrant cells called Langerhans' cells (LCs) that are derived from the bone marrow and have a macrophage lineage. During pathologic events, erythrocytes and leukocytes may also be seen in the epidermis. Finally, melanocytes, which are responsible for the formation of melanin pigment, are derived from neuroectodermal elements in neural crest. They migrate to the skin and, then, locally replicate in the skin. |
