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integumentary system.docx

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University of Toronto Scarborough
Biological Sciences
Kenneth Welch

Integumentary System Skin (Integument) • Consists of three major regions • Epidermis – outermost superficial region • Dermis – middle region • Hypodermis – deepest region 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, and 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 Layers of the Epidermis: 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 Stratum Spinosum (Prickly Layer) • Cells contain a weblike system of intermediate filaments attached to desmosomes • Melanin granules and Langerhans’ cells are abundant in this layer Stratum Granulosum (Granular Layer) • Thin; three to five cell layers in which drastic changes in keratinocyte appearance occurs • Keratohyaline and lamellated granules accumulate in the cells of this layer Stratum Lucidium (Clear Layer) • Thin, transparent band superficial to the stratum granulosum • Consists of a few rows of flat, dead keratinocytes • Present only in thick skin Stratum Corneum (Horny Layer) • Outermost layer of keratinized cells • Accounts for three quarters of the epidermal thickness • Functions • Waterproofing • Protection from abrasion and penetration • Renders the body relatively insensitive to biological, chemical, and physical assaults Dermis • Second major skin region containing strong, flexible connective tissue • Cell types include fibroblasts, macrophages, and occasionally mast cells and white blood cells • Composed of two layers – papillary and reticular Dermis: Papillary Layer • Papillary layer • Areolar connective tissue with collagen and elastic fibers • Its superior surface contains peglike projections called dermal papillae • Dermal papillae contain capillary loops, Meissner’s corpuscles, and free nerve endings Dermis: Reticular Layer • Reticular layer • Accounts for approximately 80% of the thickness of the skin • Collagen fibers in this layer add strength and resiliency to the skin • Elastin fibers provide stretch-recoil properties Hypodermis • Subcutaneous layer deep to the skin • Composed of adipose and areolar connective tissue 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; secret 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 and secrete cerumen • Mammary glands – specialized sweat glands that secret milk Sebaceous Glands • Soften skin when stimulated by hormones • Simple alveolar glands found all over the body • Secrete an oily secretion called sebum Hair • Helps maintain warmth, alerts the body to presence of insects on the skin, and guards the scalp against physical trauma, heat loss, and sunlight • Filamentous strands of dead keratinized cells produced by hair follicles • Contains hard keratin, which is tougher and more durable than the soft keratin of the skin • Made up of the shaft projecting from the skin and the root embedded in the skin • Consists of a core called the med
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