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Epithelialtissue-overviewLocation- Firstimportanttissueinthebody,besidemuscletissue,nervoustissueand

connectivetissue.- Coversallexternalsurfacesofthebody,linealltheinternalcavitiesandthose

tubesthatcommunicatewiththeexterior,formvariousorgansandglands,andlinetheirducts.

- Allepithelialtissueareavascularnovessels.Gettheirnutritionfromtransportofoxygenandmetabolitiesthroughthebasallamina.

Basementmembrane(BM)- Vitreous(glasslignende)homogenousmembrane(ine.g.trachea)- VisibleunderLightMicroscope(LM,underPAS-positivelayer)- Consistof:

o Laminalucidao Laminadensa

ComponentsofBasallaminao Anchoringfibrils(collagenVII)

Frombasallaminaconnectbasallaminawithreticularlamina.o Reticularlamina

Productofconnectivetissueducts.Canberecognizedbydarklinesinlightmicroscope(LM)- Function

o Supporting(E.g.coveringepithelium)o Barriertocorpuscularmaterialbetweenconnectivetissue(CT)andother

tissues

o Necessaryforintercellularinteractions(e.g.reinnervationofdenervatedmusclefibres)

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BasallaminaJunctionbetweenepitheliumandconnectivetissue

- DesmosomesSpecializedintercellularjunctionsbetweenthecells- HemidesmosomeParticipateinjunctionwithbasallaminaproductof

epithelium,atthebottomofepitheliumCanseetinywhitecellsbetweenepitheliumandbasallamina.ThisisLaminalucida.

Justunderyoucanseatinydarklineofcells.Thisislaminadensa.Togethertheycreatethebasallamina.Theyareaproductofepithelialcells.

ClassificationofepithelialtissueCanbeclassifiedinthreeways:

1. Numberofcelllayers:

a. Singlelayer:Simpleepitheliumb. Severallayers:Stratifiedepithelium

2. Shapeofcomponentcells:a. SquamousFlattenedb. CuboidalCube-formedc. ColumnarColumn-shaped

i. Instratifiedepitheliatheshapeoftheoutermostlayerofcellsdeterminesthedescriptiveclassification.

3. PresenceofsurfacespecializationsCiliaandkeratina. E.g.:thesurfaceoftheskiniscalledstratifiedsquamouskeratinizing

epithelium

i. Consistofmanylayersofsurfacecells,theyareflattenedandcoveredbytheproteinacousmaterial:keratin.

Epitheliumcanmeectoderm,mesodermorendoderm.EctodermEpithelium

MesodermEndothelium(liningofbloodandlymphaticvessels)andmesothelium(theliningofserous(prod.Serum)bodycavities)

Principalcharacteristicsofepithelialcells- Closelyadheretooneanotherbyintercellularjunctions-Verynarrow,but

therehastobesomespaceduetoexchangeofoxygenandnutrition.

- Polarelementsfreeandapical(pen)surface,protectagainstenvironmentalinfluences,lateralsurfacesandbasalsurface.Onthesevariousspecializationsarefound.

- Basalsurfaceconnectstothebasallamina.Thisnon-cellularmembraneseparatesepitheliafromunderlyingconnectivetissue.

- HavereseptorsE.g.forpain

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Classificationaccordingtotheirconstruction1. Surface(flat)epithelia

a. Oneormorecellularlayerslininganexternalorinternalsurfaceofthebody

i. Allcoveringepithelia2. Trabecularepithelia

a. Cellsforminterconnectingplatesi. Liverii. Endocrineglands

3. Reticularepithelia(Cytoreticulum)a. Anetworkofstellate(stjerneformede)epithelialreticular

(nettverksdannende)attachedtoeachotherattheendsoftheirprocesses.i. Thymus

SpecialsurfacesonepithelialcellsDifferentsurfacesontheirapicaloruppersurfaces.

- Thesemodificationsare:o Cilia

Motile(capableofmotion)structures Foundine.g.uterustubes,uterus(livmor)andtubesin

respiratorysystem.o Microvilli

Small,non-motileprojections(utstikkere) Coversallabsorptivecellsine.g.thesmallintestineand

proximalconvolutedtubulesinthekidney.

o Stereocilia Long,non-motilebranchesmicvrovilli

Coversthecellsintheepididymis(bitestikkel)andvasdeferens(sdleder)

Functionofmicrovilliandstereociliaisabsorptionoptimizeabsorptionthrough

extendedareal.

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Classificationofcovering(surface)epitheliaandexamples

Simpleepithelium

Alwaysfoundatsurfacesinvolvedinselectivediffusion,absorptionand/orsecretion.Protectagainstmechanicalabrasion.Differinthree3Dstructures:

- Squamous

o Oftenfoundliningsurfacesinvolvedinpassivetransport(diffusion)ofeithergases(asinlunges)orfluids(asinthewallsofbloodcapillaries)

o Flat,endotheliumcovers: Liningofbloodvessels Lymphaticvessels Heartcavity

o Mesotheliumcovers: Liningofbodycavities

- Cuboidalo Nucleusoftenroundandincenterofcell.o Linessmallductsandtubulesthatmayhaveexcretory,secretoryor

absorptivefuncions.

o 4-edges,sometimes6becausestructureisnothardorlikefirmboxes. Choroidplexus(somebrainstructure) Epitheliumofovary(eggstokk) Subscapularepitheliumontheanteriorsurfaceofthelens Smallductsofglands

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Choroid plexus

- Columnaro Nucleiareelongated(langstrakte)andmaybelocatedtowardsthebase,

thecentreoroccasionallytheapex(toppen)ofthecytoplasm.Thisisknownaspolarityofthenucleus.

o Withcilia Oviduct(eggleder)anduterus(livmor)

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o Withoutcilia Intestine Gallbladder Collectingtubulesandpapillaryductsinkidney

Jejunum Duodenum

StratifiedepitheliumMeansseverallayersofcells.E.g.intheskinwehavehundredsoflayers.Stratum=Layersstratified.

Onlythebasallayerofthecellsrestonthebasementmembrane.Theotherpreviouscells.

Dividesinto:

- Stratifiedsquamouso Basalcellsarecuboidalorcolumnarthesecellsmigratetowardsthe

surfaceandbecomesquamous.Totypes:keratinizedandnon-keratinized.

Keratinized Foundinexposedsurfacesofbodysuchasskin. Non-living,keratinizedandfilledwiththeproteinkeratin.

Palmandsoleshaveespeciallythicklayersofkeratinizedcells.

Non-keratinized Superficiallayerareliving,withanucleus.Coversmoist

cavities,suchas:mouth,pharynx,esophagus,vaginaandanalcanal.

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Stratisfiedsquamousnon-keratinizedepithelium(lip) Stratisfiedsquamouskeratinizedepithelium(lip)

Keratinizedstratifiedsquamousepithelium

- Stratifiedcuboidalandstratifiedcolumnar

o Limiteddistributedinthebodyo Thin,stratifiedepitheliumthatusuallyconsistofonlytwoorthreelayers

ofcuboidal/columnarcells.

Linethelargerexcretoryductsofexocrineglandssuchasthesalivaryglands.(spyttkjertler)

Linethelargerexcretoryductsofthepancreas,salivaryglandsandsweatglands

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Ductofsweatgland

PseudostratifiedepitheliumPseudo=Notgenuine(gr.)Looklikestratified,butarepracticallysimplebecauseallofthecellsrestonthebasal

membranetherearenolayersofcells.

- Canbedistinguishedfromtruestratifiedepitheliabythreecharacteristics:o Polarity

Nucleiismainlyconfinedtothebasaltwo-thirdsoftheepithelium. Nucleiisondifferentvariouslevels.

oCiliaareneverpresentontruestratifiedepithelia.Itispresentonpseudostratifiedepithelia.

Foundexclusivelyinairwaysofrespiratorysystemofmammalsthereforealsocalledrespiratoryepithelium

o AllcellsrestonthebasallaminaTherearenolayersofcells.

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TransitionalepitheliumOnlyfoundinurinarytractthereforealsocalledurothelium.

Namedtransitionalbecauseitscellstructuresaresomewherebetweenstratifiedcuboidalandstratifiedsquamousepithelia(thereoftranstitional)

Multiplelayersofepitheliumthatcancontractandexpand.

Contractedstate

- About4-5celllayersthick- Basalcellsareroughlycuboidal- Intermediatecellsarepolygonal- Surfacecellsareshapedasdomecellslarge,roundedandmaycontaintwo

nuclei.

Stretchedstate- 2-3layersthick- Intermediateandsurfacelayersareextremelyflattened.

Transitionalepithelium(urothelium)

Emptyurinarybladder Fullurinarybladder

Sources:

- Lecturesinhistologyclass- www.lfhk.cuni.cz/histologie-alsosomepictures- WeathersFunctionalHistology(5thedition)- diFioresAtlasofHistology(10thedition)