Anatomy & Physiology

Anatomy & Physiology Study Guide

6.1 The Cutaneous Membrane The Epidermis Stratified squamous epithelium makes up the epidermis. This layer is avascular. Without local blood vessels, epidermal cells receive nutrients and oxygen by diffusion from capillaries located in the dermis. The cells found in the epidermis are: keratinocytes, which produce the fibrous protein keratin, melanocytes that produce the brown pigment melanin, Langerhans’ cells , which are epidermal macrophages that help activate the immune system, and Merkel cells , which function as touch receptors in association with sensory nerve endings. The word stratum means “layer.” The strata of the epidermis are the stratum germinativum, the stratum spinosum, the stratum granulosum, the stratum lucidum, and the stratum corneum. Stratum Germinativum The innermost epidermal layer is the stratum germinativum, or stratum basale. This layer and the underlying dermis interlock, increasing the strength of the bond between the epidermis and dermis. The stratum germinativum forms epidermal ridges, which extend into the dermis and are adjacent to dermal projections called dermal papillae that project into the epidermis. The contours of the skin surface follow the ridge patterns. Ridge shapes are genetically determined. The pattern of the epidermal ridges is unique and does not change with aging. The ridge patterns on the tips of the fingers are the basis of fingerprints. Stratum Spinosum Stratum spinosum consists of 8-10 layers of keratinocytes bound together by desmosomes. Some of the cells entering this layer from the stratum germinativum continue to divide, further increasing the thickness of the epithelium. The stratum spinosum also contains Langerhans cells, which participate in the immune response by stimulating a defense against microorganisms that manage to penetrate the superficial layers of the epidermis and superficial skin cancers. Stratum Granulosum The next layer is called the “grainy layer” or stratum granulosum and lies superficial to the stratum spinosum. The stratum granulosum consists of keratinocytes in three to five layers derived from the stratum spinosum. Most cells at this layer have stopped dividing and started making large amounts of the protein keratin. Keratin is the structural component of hair and nails in humans. As keratin fibers develop, the cells grow thinner and flatter, and their membranes thicken and become less permeable. Stratum Lucidum The stratum lucidum is a glassy clear layer that covers the stratum granulosum. This thick skin found on the palms and soles has cells that are flattened, densely packed, and filled with keratin.

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