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# Skin Layers and Structure * **Stratum Corneum (30-40 day life cycle):** * Up to 30 layers of dead keratinocytes, flattened and enucleated. * Still contains keratin bundles. * Eventually sloughed off as dander. * What keeps them together? Desmosomes. * **Dermis:** * Connective...

# Skin Layers and Structure * **Stratum Corneum (30-40 day life cycle):** * Up to 30 layers of dead keratinocytes, flattened and enucleated. * Still contains keratin bundles. * Eventually sloughed off as dander. * What keeps them together? Desmosomes. * **Dermis:** * Connective tissue layer beneath the epidermis. * Sweat and sebaceous glands. Nerve endings, hair, and nail roots. * Tattoo ink must reach this layer to stay. * **Cells in Dermis:** * Fibroblasts: Produce ECM, allowing for dermis repair. * Leukocytes (white blood cells): Important in immunity. * **Upper Layer (Papillary layer):** * Areolar CT. Dermal papillae connect the dermis to the epidermis. * Fingerprints created by epidermal ridges extending downwards. * Loose organization allows for movement of leukocytes. * **Lower Layer (Reticular layer):** * Dense irregular CT with collagen and elastin fibers. * Provides strength and elasticity. * Collagen binds to water to maintain hydration. * **Hypodermis:** * Primarily adipose tissue with some areolar CT. * Common injection site. * Reservoir for energy and thermal insulation (subcutaneous fat).