Skin and Subcutaneous Tissue

From the histologic point of view, the skin varies in thickness from 1.5 to 4.0 mm and is composed of a superficial layer and a deep layer — the epidermis and the dermis, respectively (Fig. 2.1a). The epidermis is made of stratified epithelium, and can be divided into two main layers: the superficial stratum corneum, which is made of closely packed flattened dead cells, and the deep germinative zone (consisting of the stratum basale, stratum spinosum and stratum granulosum). In regions that are not subject to pressure, the epidermis is thin and hairy, whereas in areas undergoing attrition and local shocks (i.e., palms of the hands and soles of the feet), the skin is hairless and may thicken to an even greater extent as a result of a hypertrophied stratum corneum. Deep to the epidermis, the dermis is a thick layer containing large amounts of collagen and a rich network of vessels, lymphatics and nerve endings. It can be divided into a deep reticular layer, which is composed of bulky connective tissue, and a superficial papillary layer, which interdigitates with the base of the epidermis and provides an important mechanical and metabolic support to the overlying epidermis.