Chapter 5: The Integumentary System

The integumentary system represents approximately sixteen percent of total body weight and functions as the body's primary barrier against environmental hazards, pathogens, and fluid loss. This system consists of the cutaneous membrane, which includes the epidermis and dermis, along with accessory structures such as hair, nails, and exocrine glands. The epidermis is a stratified squamous epithelium lacking its own blood supply and organized into distinct layers that vary by skin thickness; thin skin contains four strata while thick skin found on palms and soles contains five, with the stratum corneum serving as a waterproof barrier of dead keratinized cells. The dermis beneath the epidermis comprises a papillary layer containing sensory receptors and capillaries and a reticular layer rich in collagen and elastic fibers that provide structural support and flexibility. Skin color results from melanin production by melanocytes in response to ultraviolet exposure, a protective mechanism that can malfunction in basal cell carcinoma or malignant melanoma. Hair follicles produce protective hair through keratinization, while sebaceous glands secrete lipid-rich sebum and sweat glands regulate thermoregulation through eccrine and apocrine secretion. The chapter addresses burn injuries classified by depth and severity, from first-degree superficial burns affecting only the epidermis to full-thickness third-degree burns destroying both epidermal and dermal layers, requiring skin grafts for healing. Skin repair occurs through sequential inflammatory, migratory, proliferative, and scarring phases, though excessive collagen deposition can produce keloid formation. The integumentary system also synthesizes cholecalciferol when exposed to ultraviolet radiation, which the body converts to calcitriol for calcium absorption and bone health. Age-related changes including reduced melanocyte activity, epidermal and dermal thinning, decreased sweat gland function, and diminished immune cell populations compromise protective and thermoregulatory functions in older individuals.