Surface Area = sq.m(1/2 white board) Weight = 4-5 kg (8-9lbs) 7% of body weight Thickness – mm Millions rub off each day- New epidermis every days

Epidermis Dermis  Composed of epithelial tissue  Outermost layer  Non-vascular  Keratinized stratified squamous epithelium  Composed of fibrous connective tissue  Underlying layer  vascularized

 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

 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

 Stratum Lucidum (clear layer)- thin, translucent, dead keratinocytes  Stratum Corneum (Horny Layer) layers thick, ¾ of epidermal thickness, 40 lbs shed in lifetime

 Thin, blood vessel rich, areolar connective, collagen and elastin fibers, loosely woven  Dermal papillae- indent overlying epidermis, touch receptors(Meissner’s corpuscles), fingerprints

 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)

 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

 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

 Bronzing-Addison’s disease, hypofunction of adrenal cortex  Black and blue marks- hematomas (bruise)

 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

 Found everywhere except palms, soles of feet  Holocrine gland  Sebum- oily  Soften and lubricates hair  Bactericidal action  Seborrhea – “cradle cap”

 Hard Keratin  content/uploads/healthy-finger-nails- diagram.gif

 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

 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

 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

 Vellus  Pale, fine  Females and children  Terminal  Coarser  Scalp and eyebrows  Androgen stimulates

 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)

 Alopecia- hair thinning or baldness  Drug induced  Excessive vitamin A  Chemotherapy  Burns  Radiation  Alopecia areata- autoimmune  Male Pattern Baldness  Minoxidil treatment

 Protection › Chemical, physical, and biological barriers  Body Temperature Regulation  Cutaneous Sensation  Metabolic Functions  Blood Reservoir  Excretion

 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)

 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

 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

 A rule : asymmetry  B rule : border irregularity  C rule: color  D rule: diameter  E rule : elevation

 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

 Lanugo coat- 5-6 month fetus, delicate coat of hairs  Vernix caseosa- cheesy substance on newborns