Stratum granulosum, 3-5 cell layers, contains diamond shaped cells with keratohyalin granules and lamellar granules. Dendritic cells can be found in this layer. Stratum spinosum, 8-10 cell layers, also known as the prickle cell layer contains irregular, polyhedral cells with cytoplasmic processes, sometimes called “spines”, that extend outward and contact neighboring cells by desmosomes. The cells found in this layer are cuboidal to columnar mitotically active stem cells that are constantly producing keratinocytes. Stratum basale, also known as stratum germinativum, is the deepest layer, separated from the dermis by the basement membrane (basal lamina) and attached to the basement membrane by hemidesmosomes. The layers of the epidermis include the stratum basale (the deepest portion of the epidermis), stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum (the most superficial portion of the epidermis). The upper back is considered thickest based on the thickness of the dermis, but it is considered “thin skin” histologically because the epidermal thickness lacks the stratum lucidum layer and is thinner than hairless skin. Hairless skin found in the palms of the hands and soles of the feet is thickest because the epidermis contains an extra layer, the stratum lucidum. The thickness of each layer of the skin varies depending on body region and categorized based on the thickness of the epidermal and dermal layers. This article discusses the relevant anatomical structures of the skin’s epidermal layer, its structure, function, embryology, vascular supply, innervation, surgical considerations, and clinical relevance. It also regulates temperature and the amount of water released into the environment. The skin's structure is made up of an intricate network which serves as the body’s initial barrier against pathogens, UV light, and chemicals, and mechanical injury. It is made up of three layers, the epidermis, dermis, and the hypodermis, all three of which vary significantly in their anatomy and function. Skin is the largest organ in the body and covers the body's entire external surface.
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