Y khoa, y dược - The integumentary system

5 The Integumentary SystemSkin (Integument)Consists of three major regionsEpidermis—superficial regionDermis—middle regionHypodermis (superficial fascia)—deepest regionSubcutaneous layer deep to skin (not technically part of skin)Mostly adipose tissueFigure 5.1EpidermisHair shaftDermisReticularlayerPapillarylayerHypodermis(superficial fascia)Dermal papillaePoreSubpapillaryvascular plexusAppendagesof skin • Eccrine sweat gland• Arrector pili muscle• Sebaceous (oil) gland• Hair follicle• Hair rootNervous structures• Sensory nerve fiber• Pacinian corpuscle• Hair follicle receptor (root hair plexus)Cutaneous vascularplexusAdipose tissueEpidermisKeratinized stratified squamous epithelium Cells of epidermisKeratinocytes—produce fibrous protein keratinMelanocytes10–25% of cells in lower epidermisProduce pigment melaninEpidermal dendritic (Langerhans) cells—macrophages that help activate immune system Tactile (Merkel) cells—touch receptorsFigure 5.2aDermisStratum corneumMost superficial layer; 20–30 layers of deadcells represented only by flat membranoussacs filled with keratin. Glycolipids inextracellular space.Stratum granulosumThree to five layers of flattened cells,organelles deteriorating; cytoplasm full oflamellated granules (release lipids) andkeratohyaline granules.Stratum spinosumSeveral layers of keratinocytes unified bydesmosomes. Cells contain thick bundles ofintermediate filaments made of pre-keratin.Stratum basaleDeepest epidermal layer; one row of activelymitotic stem cells; some newly formed cellsbecome part of the more superficial layers.See occasional melanocytes and epidermaldendritic cells.(a)Layers of the Epidermis: Stratum Basale (Basal Layer)Deepest epidermal layer firmly attached to the dermisSingle row of stem cellsAlso called stratum germinativum: cells undergo rapid divisionJourney from basal layer to surfaceTakes 25–45 days Layers of the Epidermis: Stratum Spinosum (Prickly Layer)Cells contain a weblike system of intermediate prekeratin filaments attached to desmosomesAbundant melanin granules and dendritic cells Layers of the Epidermis: Stratum Granulosum (Granular Layer)Thin; three to five cell layers in which the cells flattenKeratohyaline and lamellated granules accumulate Layers of the Epidermis: Stratum Lucidum (Clear Layer)In thick skinThin, transparent band superficial to the stratum granulosumA few rows of flat, dead keratinocytesLayers of the Epidermis: Stratum Corneum (Horny Layer)20–30 rows of dead, flat, keratinized membranous sacsThree-quarters of the epidermal thicknessFunctionsProtects from abrasion and penetrationWaterproofsBarrier against biological, chemical, and physical assaultsFigure 5.2bMelanocyteMelanin granuleTactile(Merkel) cell Sensorynerve endingEpidermaldendritic cellDermisKeratinocytesStratum corneumMost superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space.Stratum granulosumThree to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules.Stratum spinosumSeveral layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin.Stratum basaleDeepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and epidermal dendritic cells. Desmosomes(b)DermisStrong, flexible connective tissueCells include fibroblasts, macrophages, and occasionally mast cells and white blood cellsTwo layers: PapillaryReticularFigure 5.1EpidermisHair shaftDermisReticularlayerPapillarylayerHypodermis(superficial fascia)Dermal papillaePoreSubpapillaryvascular plexusAppendagesof skin • Eccrine sweat gland• Arrector pili muscle• Sebaceous (oil) gland• Hair follicle• Hair rootNervous structures• Sensory nerve fiber• Pacinian corpuscle• Hair follicle receptor (root hair plexus)Cutaneous vascularplexusAdipose tissueLayers of the Dermis: Papillary LayerPapillary layerAreolar connective tissue with collagen and elastic fibers and blood vesselsDermal papillae contain: Capillary loops Meissner’s corpusclesFree nerve endings Layers of the Dermis: Reticular LayerReticular layer~80% of the thickness of dermisCollagen fibers provide strength and resiliency Elastic fibers provide stretch-recoil propertiesSkin Markings: Friction RidgesEpidermal ridges lie atop deeper dermal papillary ridges to form friction ridges of fingerprints Figure 5.4aFriction ridges(a)Openings ofsweat gland ducts Skin Markings: Cleavage LinesCollagen fibers arranged in bundles form cleavage (tension) lines Incisions made parallel to cleavage lines heal more readilyFigure 5.4b(b)Skin ColorThree pigments contribute to skin color:MelaninYellow to reddish-brown to black, responsible for dark skin colorsProduced in melanocytes; migrates to keratinocytes where it forms “pigment shields” for nucleiFreckles and pigmented molesLocal accumulations of melaninSkin ColorCaroteneYellow to orange, most obvious in the palms and soles HemoglobinResponsible for the pinkish hue of skinAppendages of the SkinDerivatives of the epidermisSweat glandsOil glandsHairs and hair folliclesNailsSweat GlandsTwo main types of sweat (sudoriferous) glandsEccrine (merocrine) sweat glands—abundant on palms, soles, and foreheadSweat: 99% water, NaCl, vitamin C, antibodies, dermcidin, metabolic wastesDucts connect to poresFunction in thermoregulationFigure 5.5b(b) Photomicrograph of a sectioned eccrine gland (220x) Secretory cellsDermal connectivetissueDuctSebaceousglandSweat poreEccrineglandSweat GlandsApocrine sweat glands—confined to axillary and anogenital areasSebum: sweat + fatty substances and proteinsDucts connect to hair folliclesFunctional from puberty onward (as sexual scent glands?)Specialized apocrine glandsCeruminous glands—in external ear canal; secrete cerumenMammary glandsSebaceous (Oil) GlandsWidely distributedMost develop from hair folliclesBecome active at pubertySebumOily holocrine secretionBactericidal Softens hair and skin Figure 5.5a(a) Photomicrograph of a sectioned sebaceous gland (220x) Sebaceousgland ductHair inhair follicleSecretory cellsDermalconnectivetissueSebaceousglandSweatporeEccrineglandHair FunctionsAlerting the body to presence of insects on the skin Guarding the scalp against physical trauma, heat loss, and sunlightDistributionEntire surface except palms, soles, lips, nipples, and portions of external genitaliaHair Consists of dead keratinized cells Contains hard keratin; more durable than soft keratin of skinHair pigments: melanins (yellow, rust brown, black)Gray/white hair: decreased melanin production, increased air bubbles in shaftFigure 5.6aHair shaftArrectorpiliSebaceousglandHair root Hair bulb(a) Diagram of a cross section of a hair within its follicle• Connective tissue root sheath• Glassy membrane• External epithelial root sheath• Internal epithelial root sheathFollicle wall• Cuticle• Cortex• MedullaHair(b) Photomicrograph of a cross section of a hair and hair follicle (250x)• Connective tissue root sheathFollicle wall• Cuticle• Glassy membrane• Cortex• Medulla• Internal epithelial root sheath • External epithelial root sheathHairHair shaftArrectorpiliSebaceousglandHair root Hair bulbFigure 5.6bHair FollicleExtends from the epidermal surface into dermisTwo-layered wall: outer connective tissue root sheath, inner epithelial root sheathHair bulb: expanded deep end Hair FollicleHair follicle receptor (root hair plexus) Sensory nerve endings around each hair bulbStimulated by bending a hairArrector piliSmooth muscle attached to follicleResponsible for “goose bumps”Figure 5.6cHair shaftArrectorpiliSebaceousglandHair root Hair bulb(c)Diagram of a longitudinal view of the expanded hairbulb of the follicle, which encloses the matrix• Internal epithelial root sheath• External epithelial root sheath• Connective tissue root sheathFollicle wallHair matrixMelanocyteHair papillaSubcutaneous adipose tissue• Medulla• Cortex• Cuticle• Glassy membraneHair root(d) Photomicrograph of longitudinal view of the hair bulb in the follicle (160x)Follicle wallHair matrixHair papillaSubcutaneousadipose tissueHair root• Connective tissue root sheath• Glassy membrane• External epithelial root sheath• Internal epithelial root sheath• Cuticle• Cortex• MedullaHair shaftArrectorpiliSebaceousglandHair root Hair bulbFigure 5.6dTypes of HairVellus—pale, fine body hair of children and adult females Terminal—coarse, long hair of eyebrows, scalp, axillary, and pubic regions (and face and neck of males)Types of HairHair GrowthGrowth phase (weeks to years) followed by regressive stage and resting phase (1–3 months)Growth phase varies (6–10 years in scalp, 3–4 months in eyebrows)Hair Thinning and BaldnessAlopecia—hair thinning in both sexes after age 40True (frank) baldness Genetically determined and sex-influenced condition Male pattern baldness is caused by follicular response to DHTStructure of a NailScalelike modification of the epidermis on the distal, dorsal surface of fingers and toesFigure 5.7Lateralnail foldLunuleNailmatrixRoot of nailProximalnail foldHyponychiumNail bedPhalanx (bone of fingertip)Eponychium(cuticle)Bodyof nailFree edgeof nail(a)(b)Functions of the Integumentary SystemProtection—three types of barriersChemicalLow pH secretions (acid mantle) and defensins retard bacterial activityFunctions of the Integumentary SystemPhysical/mechanical barriersKeratin and glycolipids block most water and water- soluble substancesLimited penetration of skin by lipid-soluble substances, plant oleoresins (e.g., poison ivy), organic solvents, salts of heavy metals, some drugsBiological barriersDendritic cells, macrophages, and DNAFunctions of the Integumentary SystemBody temperature regulation~500 ml/day of routine insensible perspiration (at normal body temperature)At elevated temperature, dilation of dermal vessels and increased sweat gland activity (sensible perspirations) cool the body Cutaneous sensationsTemperature, touch, and painFunctions of the Integumentary SystemMetabolic functionsSynthesis of vitamin D precursor and collagenaseChemical conversion of carcinogens and some hormonesBlood reservoir—up to 5% of body’s blood volumeExcretion—nitrogenous wastes and salt in sweatSkin CancerMost skin tumors are benign (do not metastasize)Risk factorsOverexposure to UV radiationFrequent irritation of the skinSome skin lotions contain enzymes in liposomes that can fix damaged DNASkin CancerThree major types:Basal cell carcinoma Least malignant, most commonSquamous cell carcinomaSecond most common MelanomaMost dangerousBasal Cell CarcinomaStratum basale cells proliferate and slowly invade dermis and hypodermisCured by surgical excision in 99% of casesFigure 5.8aSquamous Cell CarcinomaInvolves keratinocytes of stratum spinosumMost common on scalp, ears, lower lip, and handsGood prognosis if treated by radiation therapy or removed surgicallyFigure 5.8bMelanomaInvolves melanocytes Highly metastatic and resistant to chemotherapyTreated by wide surgical excision accompanied by immunotherapyMelanomaCharacteristics (ABCD rule)A: Asymmetry; the two sides of the pigmented area do not match B: Border exhibits indentationsC: Color is black, brown, tan, and sometimes red or blueD: Diameter is larger than 6 mm (size of a pencil eraser)Figure 5.8cBurnsHeat, electricity, radiation, certain chemicalsBurn (tissue damage, denatured protein, cell death)Immediate threat:Dehydration and electrolyte imbalance, leading to renal shutdown and circulatory shockRule of NinesUsed to estimate the volume of fluid loss from burnsFigure 5.9Anterior and posteriorhead and neck, 9%41/2%41/2%Anterior and posteriorupper limbs, 18%Anterior and posteriorlower limbs, 36%100%TotalsAnterior and posteriortrunk, 36%Anteriortrunk,18% 9%9%(Perineum, 1%)41/2%Partial-Thickness BurnsFirst degreeEpidermal damage onlyLocalized redness, edema (swelling), and painSecond degreeEpidermal and upper dermal damageBlisters appearFigure 5.10a(a)Skin bearing partialthickness burn (1st and 2nd degree burns) 1st degreeburn2nd degreeburnFull-Thickness BurnsThird degreeEntire thickness of skin damagedGray-white, cherry red, or blackNo initial edema or pain (nerve endings destroyed)Skin grafting usually necessaryFigure 5.10b(b)Skin bearing fullthickness burn(3rd degree burn) 3rddegreeburnSeverity of BurnsCritical if:>25% of the body has second-degree burns>10% of the body has third-degree burnsFace, hands, or feet bear third-degree burnsDevelopmental Aspects: FetalEctoderm  epidermis Mesoderm  dermis and hypodermis Lanugo coat: covering of delicate hairs in 5th and 6th monthVernix caseosa: sebaceous gland secretion; protects skin of fetusDevelopmental Aspects: Adolescent to AdultSebaceous gland activity increasesEffects of cumulative environmental assaults show after age 30Scaling and dermatitis become more commonDevelopmental Aspects: Old AgeEpidermal replacement slows, skin becomes thin, dry, and itchySubcutaneous fat and elasticity decrease, leading to cold intolerance and wrinklesIncreased risk of cancer due to decreased numbers of melanocytes and dendritic cells Skin-Burns: Study GuideSkin-Healing of Wounds: Study Guide