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Surface Area = 1.2-2.2 sq.m(1/2 white board) Weight = 4-5 kg (8-9lbs) 7% of body weight Thickness – 1.5-4.0 mm Millions rub off each day- New epidermis every 25-45 days
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Epidermis Dermis Composed of epithelial tissue Outermost layer Non-vascular Keratinized stratified squamous epithelium Composed of fibrous connective tissue Underlying layer vascularized
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Keratinocytes- produce keratin, tightly connected by desmosomes, continuous mitosis Melanocytes-pigment called melanin(protects from UV), spider-shaped cells, found in deepest layer of epidermis Merkel cells-shaped like spikey hemisphere, Merkel disc has sensory function Langerhans cells -made on bone marrow, macrophages
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Stratum Basale- ( Basal Layer) bottom, attached to dermis, youngest keratinocytes, 10-25% are melanocytes Stratum Spinosum (Prickly Layer) intermediate filaments resist tension attach to desmosomes, keratinocytes appear spiny Stratum Granulosum (Grandular layer) 3-5 layers thick, keratinocytes flatten, accumulate keratohyaline and lamellated granules
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Stratum Lucidum (clear layer)- thin, translucent, dead keratinocytes Stratum Corneum (Horny Layer)- 20-30 layers thick, ¾ of epidermal thickness, 40 lbs shed in lifetime
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Thin, blood vessel rich, areolar connective, collagen and elastin fibers, loosely woven Dermal papillae- indent overlying epidermis, touch receptors(Meissner’s corpuscles), fingerprints
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80% of thickness of dermal layer Dense irregular connective tissue Extra cellular matrix contains thick bundles of interlacing collagen fibers, form cleavage, tension and lines in the skin, flexure lines (at joints)
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Melanin- › Protects from UV › All have same number only make different amounts Carotene- › Yellow to orange › Accumulates in fatty tissue and stratum corneum (soles of feet and palms) › *Hemoglobin (found in Red blood cells) can give reddish hue
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Redness (erythema)- embarrassment, fever, hypertension, inflammation, allergy Pallor (pale)- fear, anger, stress, anemia, low blood pressure Jaundice (yellow)- liver disorder, bile pigments accumulate in body tissues, bilirubin secreted by liver cells as component of bile
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Bronzing-Addison’s disease, hypofunction of adrenal cortex Black and blue marks- hematomas (bruise)
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Nails Sweat glands (sudiferous glands) pH 4-6 › Eccrine (merocrine)-palms, soles of feet, forehead › Apocrine gland- hair follicles, body odor, musky, unknown function › Other- ceruminous glands (ear wax) › Mammary glands- milk Sebaceous glands (oil) Hair
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Found everywhere except palms, soles of feet Holocrine gland Sebum- oily Soften and lubricates hair Bactericidal action Seborrhea – “cradle cap”
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Hard Keratin http://www.thaimedicalnews.com/wp- content/uploads/healthy-finger-nails- diagram.gif
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Sense insects before they sting Head hair protects against UV, heat loss, physical trauma Eye lashes- shield eyes Nose hairs- filter large particles like lint and insects
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Pili-”hairs” consist of largely dead, keratinized cells. Hard keratin-tough and durable, individual cells do not flake off Soft Keratin- found in typical epidermal cells
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Medulla- core, large cells and air spaces, not found in fine hairs Cortex- bulky layer surrounding medulla, several layers of flattened cells Cuticle-single layer of cells, overlaps on another like shingles *Red heads have trichosiderin- iron- containing pigment
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Vellus Pale, fine Females and children Terminal Coarser Scalp and eyebrows Androgen stimulates
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Hirsutism- excessive hairiness, caused by excessive androgens 2.5 mm/week Lose about 90 hairs/day Growth cycle › Active (anagen) › Regressive ( catagen) › Resting phase (telogen)
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Alopecia- hair thinning or baldness Drug induced Excessive vitamin A Chemotherapy Burns Radiation Alopecia areata- autoimmune Male Pattern Baldness Minoxidil treatment
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Protection › Chemical, physical, and biological barriers Body Temperature Regulation Cutaneous Sensation Metabolic Functions Blood Reservoir Excretion
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Low pH retards bacterial growth (acid mantle) Natural antibiotic (human defensin) Cathelicidins – fights strep bacteria Some substances can penetrate skin, ie. Lipid-soluble substances (oxygen, Carbon dioxide, vitamins A,E,D,K), oleoresins (poison ivy)
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Organic solvents (ie. Acetone, paint thinner, etc.) Salts of heavy metals (lead, mercury, nickel) May lose 12 L of body fluid per day Can transform cortisone into hydrocortisone 5% of blood volume in skin Lose water and salt through skin
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Skin Cancer- benign and malignant, p53 gene (tumor suppressor gene) Types of Skin cancer: › 1)Basal Cell carcinoma › 2)Squamous cell carcinoma-arises from keratinocytes in stratum spinosum › 3)Melanoma- cancer of melanocytes
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A rule : asymmetry B rule : border irregularity C rule: color D rule: diameter E rule : elevation
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First degree: epidermis only damaged, redness, swelling, pain, heals in 2-3 days Second degree: epidermis and upper region of dermis, blisters, 3-4 weeks no scarring Third degree: all layers, appears gray- white, cherry red, or blackened, not painful because nerve endings, skin grafing
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Lanugo coat- 5-6 month fetus, delicate coat of hairs Vernix caseosa- cheesy substance on newborns
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