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Integumentary System Dr. Michael P. Gillespie Integumentary System The skin (cutaneous membrane) covers the external surface of the body. It is the largest organ of the body in terms of both surface area and weight. Functions of the Integumentary System Thermoregulation Reservoir for blood Protection from external environment Cutaneous sensations Excretion and absorption Vitamin D synthesis Structure of the Skin Two main parts Epidermis – epithelial tissue Dermis – connective tissue Subcutaneous layer (hypodermis) – not part of the skin – areolar and adipose tissue Contains nerve endings called lamellated (Pacinian) corpuscles Epidermis Keratinized squamous epithelium 4 types of cells 5 basic layers of the epidermis Cell Types in Epidermis Keratinocytes (90%) Keratino = hornlike; cytes = cells Keratin –protects from heat, microbes, and chemicals Melanocytes (8%) Melano = black Produce pigment melanin – absorbs UV light Langerhans cells Arise from red bone marrow – migrate to epidermis Immune response Merkel cells Tactile (Merkel) disc Layers of Epidermis Stratum Basale Stratum Spinosum Stratum Granulosum Stratum Lucidum Stratum Corneum Stratum Basale Deepest layer Single row of columnar or cuboidal keratinocytes Keratin protects the deep layers from injury Stem cells Also known as the stratum germinativum (germ = sprout) Stratum Spinosum Spinos = thornlike 8 – 10 layers of many sided keratinocytes close together Provides strength and flexibility to the skin Stratum Granulosum Middle of the epidermis Granulos – little grains 3-5 layers of flattened keratinocytes Undergoing apoptosis (cell death) Lamellar Granules – release a lipid-rich secretion Stratum Lucidum Lucid = clear Present only in the thick skin of the fingertips, palms, and soles 3-5 layers of flattened clear, dead keratinocytes Stratum Corneum Corne = horn or horny 25 – 30 layers of flattened dead keratinocytes Shed and replaced by cells from deeper strata Mostly keratin Between the cells are lipids from lamellar granules – creates water repellent barrier Protects deep layers from injury Friction creates a callus – abnormal thickening Growth of Epidermis Newly formed cells are pushed to the surface Accumulate more keratin (keratinization) Undergo apoptosis Keratinized cells slough off 4 weeks Psoriasis Common skin disorder Keratinocytes divide more quickly than normal and shed prematurely (7-10 days) Immature keratinocytes make abnormal keratin Forms flaky, silvery scales Knees, elbows, and scalp (dandruff) Tx. Topical ointments, UV phototherapy (decreases cell division) Dermis Deeper layer Mainly connective tissue Collagen and elastic tissue Fibroblasts, macrophages, and adipocytes Dermis Continued… Papillary region – dermal papillae (papillae = nipples) – indent the epidermis – capillary loops Corpuscles of touch (Meissner corpuscles) Free nerve endings – warmth, coolness, pain, tickling, and itching Dermis continued… Reticular region (reticul = netlike) – deeper part of dermis Dense irregular CT Adipose cells, hair follicles, nerves, sebaceous (oil) glands, sudoriferous (sweat) glands Striae – streaks – stretch marks Epidermal ridges – grip / friction – palms, fingers, soles, toes Types of Skin Thin skin – covers all surfaces of the body except for the palms, palmar surfaces of the digits, and soles. Lacks a stratum lucidum Thick skin – covers the palms, palmar surfaces of the fingers, and soles Distinct stratum lucidum Accessory Structure of the Skin Hair Skin glands Nails Hair Hair or pili – present on most surfaces except the palms, palmar surfaces of fingers, soles, and plantar surfaces of feet Shaft – superficial portion – projects from skin Root – deeper portion – penetrates the dermis and sometimes into the subcutaneous layer Arrector pili – muscle which pulls on hair shaft causing it to raise – emotional stress (cold or fright) Conditions Hirsutism = excessive body hair due to excessive androgens – tumor of the adrenal glands, testes, or ovaries Androgenic alopecia – male-pattern baldness Skin Glands Sebaceous Glands (greasy) – oil glands - typically connected to hair follicles Secrete sebum – coats hair and keeps it from becoming dry and brittle – keeps skin soft and pliable Sudoriferous Glands – sweat glands Eccrine – throughout skin Apocrine – skin of axilla, groin, areolae and bearded regions Ceruminous Glands – cer = wax – external ear Cerumen = earwax – creates sticky body to impede entrance of foreign substances Nails Tightly packed, hard, keratinized epidermal cells Nail body, free edge and nail root Lunula Hyponychium – beneath free edge Eponychium (cuticle) adheres to the lateral margin of the nail wall. Epidermal Wound Healing Cells enlarge and migrate across the wound Contact inhibition – when migrating cells touch one another they stop due a this cellular response Deep Wound Healing The injury extends to the dermis and subcutaneous layer Inflammatory phase Blood clot forms Inflammation eliminates wastes and microbes Migratory phase Damaged blood vessels begin to regrow Proliferative phase Extensive growth of epithelial cells Deposition of fibroblasts Maturation phase Contributions of the Integumentary System The Integumentary System contributes to the functioning of all other body systems. Refer to the table on page 155. Skin Disorders Skin Cancer Burns Pressure Ulcers Skin Cancer Almost exclusively caused by excessive exposure to the sun. Basal cell carcinomas Squamous cell carcinomas Malignant Melanomas Basal Cell Carcinoma Squamous Cell Carcinoma Detection of Malignant Melanoma A Asymmetry MM lack symmetry B Border MM have notched, indented, scalloped, or indistinct borders C Color MM have uneven coloration, may contain several colors D Diameter MM are typically greater than 6mm (0.25 in.) E Elevation Normal Nevus & Malignant Melanoma Risk Factors for Malignant Melanoma 1. Skin type Light skinned individuals who burn, but don’t tan 2. Skin exposure Sunny areas, high altitude (UV light), outdoor occupation 3. Family Hx. 4. Age 5. Immunological status Immunosuppressed individuals have a higher risk of skin cancer Burns Tissue damage caused by Excessive heat Electricity Radioactivity Corrosive chemicals Destroy some of the skin’s contributions to homeostasis Grading of Burns First-degree burn Second-degree burn (partial thickness) Third-degree burn (full thickness) Systemic Effects of Burns 1. Large loss of water, plasma, and plasma proteins (causes shock) 2. Bacterial infection 3. Reduced circulation of blood 4. Decreased production of urine 5. Diminished immune response Severity of Burns Determined by the depth of the burn and the extent of the area involved. According to the American Burn Association a major burn includes: Third-degree burns over 10% Second-degree burns over 25% Third-degree burns over face, hands, feet, or perineum When the burn area exceeds 70%, more than half of the victims die Determining the Extent of a Burn Rule of nines – a quick method for estimating the surface area affected by burns Lund-Browder method – a more accurate method for assessing the extent of burns Skin Color Melanin – causes skin color from pale yellow to black Melanocytes produce melanin Freckles and liver spots are accumulations of melanin Carotene – yellow-orange pigment Hemoglobin – imparts a red color Albinism – inability to produce melanin - missing from the hair, eyes, and skin Vitiligo – loss of melanocytes from patches of skin Skin Color Clues Cyanotic – blue - hemoglobin is depleted of oxygen Jaundice – yellow – buildup of the yellow pigment bilirubin in the blood – usually indicates liver disease Erythema – red – engorgement of capillaries in the skin – skin injury, heat, infection, inflammation, allergies Carotonemia Cyanosis Jaundice Vitiligo Scabies