Functions of the skin:Protection: chemical, physical, biologicalBody temperature regulation: sweat glands; presence of blood vessels in the dermis and below (blood flow)Cutaneous sensation: hot; cold; pain; discriminative touchMetabolic function: chemical conversion; conversion of vitamin D from inactive to active via sunlightBlood reservoir: blood vessels in dermis and below; blood is stored there when not physically activeSecretion: sweat; oil; protect us from environmentThe skin is composed of 2 distinctions regionEpidermisComposed of 4 different types of cells1. Keratinocytes: produce keratin (makes more resilient); connected to desmosomes; arise form a deeper mitotically active layer (basal layer); dead at surface (turnover 25-45 days)2. Langerhans cells: macrophage cells; activate immune system3. Merkel cells: epidermal-dermal junction; associated with sensory nerve endings; receptor for touch4. Melanocytes: synthesize melanin which is taken up by keratinocyes; found in deepest layers; responsible for skin color; melanin protects us from UV light which prevent DNA from being damagedMay have 4 or 5 different layers (only on palms of hands and soles of our feet do we have 5 layers)1. Stratum basale: adjacent to the dermis; deepest layer, attached to dermis single row of youngest keratinocytes and melanocyte cells; merkel cells located here to communicate with nerve endings in dermis2. Stratum spinosum: thickest layer; made up of functional living keratinocytes; soft keratin produced during this layer and connect to desmosomes; langerhan cells also found her3. Stratum granulousum: few cells thick; cells are committing apoptosis (dying); when they exit this face they will lack organelles and will just be membranes filled with keratin; start to flatten out4. Stratum lucidum (ONLY LOCATED IN PALMS AND SOLES): made up of a single layer of cells; clear5. Stratum corneum: flat, dead, and squamous like appearance; several layers thick; oil secreted onto the skin makes this layer waterproofDermisHas two layers of connective tissue which include other cell types and structures1. Papillary layer: made of loose areolar connective tissue; where papillae are located (increases surface area btw. Dermis and epidermis)2. Reticular layer: dense irregular connective tissueBoth contain blood vesselsCleavage linesCollagen fibers arranged in bundles form cleavage (tension) linesIncisions made parallel to cleavage lines heal more readilySkin appendagesAre derivatives of epidermis with a role in maintaining homeostasisSweat glands (sudoriferous glands) (merocrine): found everywhere except nipples and external genitals1. Eccrine swear gland: most abundant; high density on palms, sole of foot and forehead; secrete sweat; hypotonic blood filtrate; 99% H2O, some NaCl, other material acidic (ph 4-6)2. Apocrine: confined to axillary and anogenital area, little role in thermoregulation; larger, ducts empty into hair follicles3. Sebaceous (oil) glands puke to keep your skin soft and smooth; alveolar glands; everywhere except palms and soles of feet; secrete sebum (holocrine); lipid and cell fragments; function in lubrication; skin (slowing water loss); hair (prevents brittleness); bactericidal function; stimulated by androgensAcnes develops when:i. Hair follicles become plugged; sebum and dead skin cellsii. Bacteria then trigger inflammation and injectionStages of acnei. Normal follicleii. Open comedone (blackhead)iii. Closed comedone (whitehead)iv. Papulev. PustuleWhy do we have hairNerve endings attached to the end of hair folliclesAlerts us to the environmentHair blocks scalp from lightHair in nose blocks dirt particlesHair is distributed over the entire skin surface expect: palms, soles, and lips; nipples and portions of the external genitaliaHair is filamentous strands of dead keratinized cellsShaft projecting from the skinRoot embedded in the dermisCells contain hard keratinConsist of 3 layers of cells:1. Medulla2. Cortex3. CuticleWhat are split ends: when the end of the hair frays due to the loss of cuticleHair follicleFollicle wall: connective tissue root sheath; glassy membrane; external epithelial root sheath; internal epithelial root sheathHair root: cuticle; cortex; medullaHair matrix: epithelial cells responsible for producing the hairHair papillaMelanocyte: produce colorSubcutaneous adipose tissueTypes of hairTerminal: hair on scalpVellus: peach fuzz; may be long enough to project through the skin, may not beGrowth of hair: 2.5 mm/weekGrowth cycles: active/dormantLose ~ 90 hairs per day; terminal to vellus and vice versaAlopecia: inbalance between terminal and vellus; hair thinningTrue or frank baldnessGenetically determined and sex-influenced conditionMale pattern baldness-caused by follicular response to DHT (testosterone); causes hair follicles to go into dormant cyclePassed down from mother on the X chromosomeSkin CancerBasal cell carcinoma (most mild)Least malignantStratum basale cells proliferate and invade dermisSun exposed areas more commonDoesn’t spread easily; is malignantCircular but has divot in the centerSquamous cell CarcinomaKeratinocytes of the stratum spinosumGrows rapidly; metastasizes, good outcome if caught earlyDiscoloration and larger ulceration in the centerMelanomaMost dangerous, highly metastic, chemotherapy resistantCancer of melanocytes1/3 from pre-existing molesspreads downward and lateral, and very earlycells take up residence in other portions of the bodyIdentifying Skin CancerABCD RuleAsymmetry: two sides don’t matchBorder irregularity: indentations in borderColor: pigmented spot contains several black colorsDiameter: larger than 6 mm diameterClassification of tissue injury by burnsFirst degree: only the epidermis is damagedSymptoms include localized redness, swelling, and painSecond degree: epidermis and upper regions of dermis are damagedSymptoms mimic first degree burns, but blisters also appear; cells are killed in this layerThird degree burn: entire thickness of the skin is damagedBurned are appears gray-white, cherry red, or black; there is no initial adema or pain (since nerve endings are destroyed); lose sweat glands, layer that protects fluid loss, etc.Dehydration and infectionA simple rule of thumb to quantify area burnedBurns considered critical if:Over 25 percent of the body has second degree burnsOver 10 percent of the body has third degree burnsThere are third degree burns on face, hands, or feetRule of ninesTool to estimate body fluid lost1.