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Integument Developmental Aspects: Adolescent to Adult Skin and hair become oilier and acne may appear Skin shows the effects of cumulative environmental assaults around age 30 Scaling and dermatitis become more common Developmental Aspects: Old Age Epidermal replacement of cells slows and skin becomes thinner Skin becomes dry and itchy Subcutaneous fat layer diminishes, leading to intolerance of cold Decreased elasticity and loss of subcutaneous tissue leads to wrinkles Decreased numbers of melanocytes and Langerhans' cells increase the risk of skin cancer Epidermis Composed of keratinized stratified squamous epithelium consisting of: four distinct cell types and four or five layers Cell types include: keratinocytes, melanocytes, Merkel cells, Langerhans' cells Outer portion of the skin is exposed to the external environment and functions in protection Cells of the Epidermis Keratinocytes ? produce the fibrous protein keratin Melanocytes ? produce the brown pigment melanin Langerhans' cells ? epidermal macrophages that help activate the immune system Merkel cells ? function as touch receptors in association with sensory nerve endings Skin (Integument) Layers of the Epidermis Epidermal Layers: Stratum Basale (Basal Layer) Deepest epidermal layer Firmly attached to the dermis Consists of a single row of the youngest keratinocytes Cells undergo rapid division, hence its alternate name, stratum germinativum Epidermal Layers: Stratum Spinosum (Prickly Layer) Cells contain a weblike system of intermediate filaments attached to desmosomes Melanin granules & Langerhans' cells are abundant in this layer Epidermal Layers: Stratum Granulosum (Granular Layer) Thin Three to five cell layers Keratinocytes change appearance drastically Granules accumulate Epidermal Layers: Stratum Lucidum (Clear Layer) Thin, transparent band Superficial to the stratum granulosum A few rows of flat, dead keratinocytes Present only in thick skin Soles of feet Palms of hands Elbows Epidermal Layers: Stratum Corneum (Horny Layer) Outermost layer of keratinized cells Accounts for three quarters of the epidermal thickness Functions include: Waterproofing Protection from abrasion and penetration Renders body relatively insensitive to biological, chemical, and physical assaults Dermis Second major skin region Contains strong, flexible connective tissue Cell types include fibroblasts macrophages occasionally mast cells and white blood cells Composed of two layers ? Papillary Reticular Layers of the Dermis: Papillary Layer Areolar connective tissue collagen and elastic fibers Surface contains nipplelike projections called dermal papillae ?(papilla' = ?nipple') Dermal papillae contain capillary loops Meissner's corpuscles free nerve endings Layers of the Dermis: Reticular Layer 80% of the thickness of the skin Collagen fibers add strength and resiliency to the skin Elastin fibers provide stretch-recoil properties Hypodermis Subcutaneous layer deep to the skin Adipose connective tissue Areolar connective tissue Blood vessels Skin Color Three pigments contribute to skin color Melanin ? yellow to reddish-brown to black pigment responsible for dark skin colors Freckles and pigmented moles ? result from local accumulations of melanin Carotene ? yellow to orange pigment most obvious in the palms and soles of the feet Hemoglobin ? reddish pigment responsible for the pinkish hue of the skin Sweat Glands Different types prevent overheating of the body; secrete cerumen and milk Eccrine sweat glands ? found in palms, soles of the feet, and forehead Apocrine sweat glands ? found in axillary and anogenital areas Ceruminous glands ? modified apocrine glands in external ear canal that secrete cerumen Mammary glands ? specialized sweat glands that secrete milk Sebaceous Glands Simple alveolar glands found all over the body Soften skin when stimulated by hormones Secrete an oily secretion called sebum Glands Specialized Integumentary Structures: Nails Scalelike modification of the epidermis on the distal, dorsal surface of fingers and toes Specialized Integumentary Structures: Hair Made up of: the shaft projecting from the skin the root embedded in the skin Consists of: a core called the medulla a cortex and an outermost cuticle Pigmented by melanocytes at the base of the hair Hair Function and Distribution Why do we have hair? Helps to maintain warmth Alerts the body to presence of insects on the skin Guards the scalp against physical trauma, heat loss, and sunlight Hair is distributed over the entire body except: Palms, soles, and lips Nipples and portions of the external genitalia Hair Follicle Root sheath: extends from the epidermal surface into the dermis Deep end is expanded forming a hair bulb A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb Bending a hair stimulates these endings our hairs act as sensory receptors Hair Follicle Hair Follicle Types of Hair Vellus ? pale, fine body hair found in children and the adult female Terminal ? coarse, long hair eyebrows scalp axillary region pubic regions Hair Thinning and Baldness Alopecia ? hair thinning in both sexes True, or frank, baldness Genetically determined Sex-influenced condition Male pattern baldness Functions of the Integumentary System Protection ? chemical, physical, and mechanical barrier Body's first line of defense! Body temperature regulation is accomplished by: Dilation (cooling) & constriction (warming) of dermal vessels Increasing sweat gland secretions to cool the body Cutaneous sensation ? exoreceptors sense touch and pain Squamous Cell Carcinoma Burns: Classification Rule of Nines