Ajman University of Science & TechnologyAjman University of Science & TechnologyAjman University of Science & TechnologyAjman University of Science & Technology

Faculty of DentistryFaculty of Dentistryy f yy f y

Histology & Cell BiologyHistology & Cell Biology

08 01 11208 01 112

Dr. AlDr. Al--Moutassem Billah KhairMoutassem Billah Khair

Epithelial TissuesEpithelial TissuesEpithelial TissuesEpithelial Tissues

Epithelial TissuesEpithelial TissuesEpitheliaEpithelia areare aa diversediverse groupgroup ofof tissuestissues whichwhich covercover oror lineline allallbodybody surfacessurfaces cavitiescavities andand tubestubes thusthus functionfunction asas interfaceinterfacebodybody surfaces,surfaces, cavitiescavities andand tubes,tubes, thusthus functionfunction asas interfaceinterfacebetweenbetween differentdifferent biologicalbiological compartmentscompartments..SurfaceSurface epitheliaepithelia formform continuouscontinuous sheetssheets comprisingcomprising oneone oror moremore layerslayers ofofSurfaceSurface epitheliaepithelia formform continuouscontinuous sheetssheets comprisingcomprising oneone oror moremore layerslayers ofofcellscells..

TheThe cellscells areare separatedseparated byby aa minuteminute quantityquantity ofof intercellularintercellular materialmaterial..TheThe cellscells areare separatedseparated byby aa minuteminute quantityquantity ofof intercellularintercellular materialmaterial..

EpithelialEpithelial cellscells areare closelyclosely boundbound toto oneone anotheranother byby aa varietyvariety ofof membranemembranespecializationsspecializations calledcalled cellcell junctionsjunctions..pp dd juju

AllAll epitheliaepithelia areare supportedsupported byby aa basementbasement membranemembrane..

EpithelialEpithelial cellcell nucleinuclei havehave aa variablevariable shapeshape (spherical(spherical toto elongatedelongated ororEpithelialEpithelial cellcell nucleinuclei havehave aa variablevariable shapeshape (spherical(spherical toto elongatedelongated ororelliptic),elliptic), whichwhich oftenoften correspondscorresponds roughlyroughly toto thethe cellcell shapeshape..

Epithelial TissuesEpithelial Tissuespp

EpithelialEpithelial tissuestissues maymay bebe derivedderived fromfrom::

EctodermEctoderm:: likelike skin,skin, oraloral cavity,cavity, anus,anus, ear,ear, nose,nose, eye,eye, enamel,enamel,pituitary,pituitary, mammary,mammary, andand sweatsweat glandsglands..p yp y yy gg

MesodermMesoderm:: twotwo typestypes

-- thethe lininglining ofof bloodblood andand lymphaticlymphatic vesselsvessels (termed(termed endothelium)endothelium)thethe lininglining ofof bloodblood andand lymphaticlymphatic vesselsvessels (termed(termed endothelium)endothelium)..

-- thethe lininglining ofof thethe serousserous cavitiescavities (termed(termed mesothelium)mesothelium)..

E d dE d d i i li i l ii iiEndodermEndoderm:: gastrointestinalgastrointestinal tracttract;; respiratoryrespiratory tracttract;; urinaryurinarybladderbladder;; liverliver andand pancreaspancreas;; thyroidthyroid andand parathyroidparathyroid glandsglands;;

dd li rli r l dl dandand salivarysalivary glandsglands..

Epithelial derivatives of embryonic germ layersEpithelial derivatives of embryonic germ layers

Germ layerGerm layer Epithelial DerivativesEpithelial DerivativesEctodermEctoderm 1.1. Skin.Skin.

2.2. Sweat gland &ducts.Sweat gland &ducts.3.3. Lining of oral cavity & vaginal & anal canal.Lining of oral cavity & vaginal & anal canal.

MesodermMesoderm 1.1. Endothelium lining blood vessels.Endothelium lining blood vessels.2.2. Mesothelium lining body cavities.Mesothelium lining body cavities.33 Lining of genital & urinary ducts & tubulesLining of genital & urinary ducts & tubules3.3. Lining of genital & urinary ducts & tubules.Lining of genital & urinary ducts & tubules.

EndodermEndoderm 1.1. Lining of esophagus.Lining of esophagus.22 Lining of gastrointestinal tract.Lining of gastrointestinal tract.2.2. Lining of gastrointestinal tract.Lining of gastrointestinal tract.3.3. Lining of gallbladder .Lining of gallbladder .4.4. Solid glands such as the liver & pancreas.Solid glands such as the liver & pancreas.g pg p5.5. Lining of respiratory system pseudostratified ciliated Lining of respiratory system pseudostratified ciliated

columnarcolumnar

Epithelial TissuesEpithelial TissuesFunctionsFunctions ofof epitheliaepithelia::

CoveringCovering andand lininglining ofof bodybody surfaces,surfaces, soso everythingeverything thatthat entersentersC gC g gg ff yy f ,f , y gy goror leavesleaves thethe bodybody mustmust crosscross themthem..

AbsorptionAbsorption (like(like:: productsproducts ofof digestion)digestion)AbsorptionAbsorption (like(like:: productsproducts ofof digestion)digestion)

DiffusionDiffusion (like(like:: lungs,lungs, bloodblood vesselsvessels ……))

SecretionSecretion (like(like:: glands)glands)SecretionSecretion (like(like:: glands)glands)

SensationSensation (like(like:: olfactoryolfactory epithelium,epithelium, tastetaste buds,buds, ……))

ProtectionProtection (against(against:: mechanicalmechanical injuryinjury dehydrationdehydration infectioninfectionProtectionProtection (against(against:: mechanicalmechanical injury,injury, dehydration,dehydration, infectioninfectionandand alsoalso fromfrom radiantradiant energy)energy)

ContractilityContractility (myoepithelial(myoepithelial cells)cells)ContractilityContractility (myoepithelial(myoepithelial cells)cells)

ReproductionReproduction (germinal(germinal oror seminiferousseminiferous epithelium)epithelium)

Epithelial TissuesEpithelial TissuesClassificationClassification ofof epitheliaepithelia

i h lii h li di i lldi i ll l ifi dl ifi d didiEpitheliaEpithelia areare traditionallytraditionally classifiedclassified accordingaccording toto::TheThe numbernumber ofof cellcell layerslayers:: aa singlesingle layerlayer (simple(simple epithelium)epithelium) oror twotwo oror moremorela rla r ( tratifi d( tratifi d ith li )ith li )layerslayers (stratified(stratified epithelium)epithelium)..

TheThe shapeshape ofof cellscells:: thisthis isis basedbased onon thethe appearanceappearance inin sectionsection takentaken atat rightrightanglesangles toto thethe epithelialepithelial surfacesurface.. InIn stratifiedstratified epitheliaepithelia thethe shapeshape ofof thetheanglesangles toto thethe epithelialepithelial surfacesurface.. InIn stratifiedstratified epitheliaepithelia thethe shapeshape ofof thethesurfacesurface layerlayer determinesdetermines thethe typetype (squamous,(squamous, cuboidalcuboidal andand columnar)columnar)..

TheThe presencepresence ofof surfacesurface specializationspecialization likelike microvillimicrovilli andand ciliacilia (only(only withwithpp ff ff pp ( y( ysimplesimple columnar)columnar) andand keratinkeratin (only(only withwith stratifiedstratified squamous)squamous)..

EpitheliaEpithelia areare alsoalso divideddivided intointo twotwo mainmain groupsgroups accordingaccording tototheirtheir structurestructure andand functionfunction:: coveringcovering andand glandularglandular epitheliaepithelia..

Epithelial TissuesEpithelial Tissuespp

SimpleSimple squamoussquamous epitheliumepithelium::pp qq ppisis composedcomposed ofof flattened,flattened, irregularlyirregularly shapedshaped cellscells formingforming aa continuouscontinuoussurfacesurface.. TheThe termterm squamoussquamous derivesderives fromfrom thethe comparisoncomparison ofof thethe cellscells toto thethescalesscales ofof thethe fishfish..

isis foundfound lininglining surfacessurfaces involvedinvolved inin diffusiondiffusion ofof eithereither gasesgases (as(as inin thethel )l ) fl idfl id (( ii hh llll ff bl dbl d ill i )ill i )lungs),lungs), oror fluidsfluids (as(as inin thethe wallswalls ofof bloodblood capillaries)capillaries)..

formsforms thethe delicatedelicate lininglining ofof thethe pleural,pleural, pericardialpericardial andand peritonealperitoneal cavitiescavitieswherewhere itit permitspermits passagepassage ofof tissuetissue fluidfluid intointo andand outout ofof thesethese cavitiescavitieswherewhere itit permitspermits passagepassage ofof tissuetissue fluidfluid intointo andand outout ofof thesethese cavitiescavities..

thethe nuclearnuclear chromatinchromatin isis condensedcondensed andand thethe cytoplasmcytoplasm isis sparsesparse andandcontainscontains fewfew organellesorganelles whichwhich reflectreflect thethe minimalminimal metabolicmetabolic activityactivity ofofff gg ff yy ffthesethese cellscells..

Epithelial TissuesEpithelial Tissuespp

SimpleSimple cuboidalcuboidal epitheliumepithelium::pp pprepresentsrepresents anan intermediateintermediate formform betweenbetween simplesimple squamoussquamous andand simplesimplecolumnarcolumnar epitheliumepithelium..

inin sectionsection perpendicularperpendicular toto thethe basementbasement membrane,membrane, itsits cellscells appearappear squaresquare ;;onon surfacesurface view,view, however,however, thethe cellscells areare actuallyactually polygonalpolygonal inin shapeshape..

thethe nucleusnucleus isis usuallyusually roundround andand locatedlocated inin thethe centrecentre ofof thethe cellcell.. ReflectingReflectingthethe considerableconsiderable metabolicmetabolic activityactivity ofof thesethese cells,cells, thethe nuclearnuclear chromatinchromatin isisrelativelyrelatively disperseddispersed andand nucleolinucleoli areare prominentprominentrelativelyrelatively disperseddispersed andand nucleolinucleoli areare prominentprominent..

usuallyusually lineslines smallsmall ductsducts andand tubulestubules whichwhich maymay havehave excretory,excretory, secretorysecretoryoror absorptiveabsorptive functionsfunctions (examples(examples areare thethe smallsmall collectingcollecting ductsducts ofof thethepp ff ( x p( x p gg ffkidney,kidney, salivarysalivary glandsglands andand pancreas)pancreas)..

Epithelial TissuesEpithelial TissuesppSimpleSimple columnarcolumnar epitheliumepitheliumisis similarsimilar toto simplesimple cuboidalcuboidal butbut itsits cellscells areare tallertaller andand appearappear columnarcolumnar ininsectionssections atat rightright anglesangles toto thethe basementbasement membranemembrane..

thethe heightheight ofof thethe cellscells maymay varyvary fromfrom lowlow toto talltall columnarcolumnar..

thethe nucleinuclei areare elongatedelongated andand maymay bebe locatedlocated towardstowards thethe base,base, thethe centrecentre ororhh ff hh ll l il ithethe apexapex ofof thethe cytoplasmcytoplasm-- polaritypolarity..

isis mostlymostly foundfound onon highlyhighly absorptiveabsorptive surfacessurfaces suchsuch asas inin thethe smallsmall intestineintestineandand gallgall bladderbladder althoughalthough itit maymay constituteconstitute thethe lininglining ofof highlyhighly secretorysecretoryandand gallgall bladder,bladder, althoughalthough itit maymay constituteconstitute thethe lininglining ofof highlyhighly secretorysecretorysurfacessurfaces suchsuch asas thatthat ofof thethe stomachstomach..

thethe apicalapical surfacesurface ofof highlyhighly absorptiveabsorptive epithelialepithelial cellscells oftenoften containscontainspp ff ff g yg y pp pp ffmicrovillimicrovilli whichwhich greatlygreatly increaseincrease thethe absorptiveabsorptive surfacesurface areaarea..

SimpleSimple columnarcolumnar ciliatedciliated epitheliumepitheliumisis describeddescribed asas aa separateseparate typetype becausebecause ofof thethe presencepresence ofof ciliacilia onon thetheisis describeddescribed asas aa separateseparate typetype becausebecause ofof thethe presencepresence ofof ciliacilia onon thethemajoritymajority ofof thethe cellcell..

eacheach cellcell maymay havehave upup toto 300300 ciliacilia whichwhich movemove toto propelpropel fluidfluid oror minuteminuteyy pp p pp p ffparticlesparticles overover thethe epithelialepithelial surfacesurface..

isis notnot commoncommon inin humanshumans exceptexcept inin thethe femalefemale reproductivereproductive tracttract..

betweenbetween ciliatedciliated cellscells areare scatteredscattered nonnon--ciliatedciliated cellscells whichwhich usuallyusually havehave aasecretorysecretory functionfunction

Epithelial TissuesEpithelial TissuesppPseudostratifiedPseudostratified columnarcolumnar ciliatedciliated epitheliumepitheliumthethe namename isis derivedderived fromfrom thethe appearanceappearance ofof thisthis epitheliumepithelium inin sectionsection whichwhichgivesgives wrongwrong impressionimpression thatthat therethere isis moremore thanthan onon layerlayer ofof cellscells..

ll h lh l llll llll hh bb bbisis truetrue simplesimple epitheliumepithelium sincesince allall cellscells restrest onon thethe basementbasement membranemembrane..

thethe nucleinuclei ofof thesethese cellscells howeverhowever areare disposeddisposed atat differentdifferent levels,levels, thusthusgivinggiving thethe wrongwrong cellularcellular stratificationstratificationgivinggiving thethe wrongwrong cellularcellular stratificationstratification..

notnot allall cellscells extendextend toto thethe luminalluminal surfacesurface butbut allall adhereadhere toto basalbasal laminalamina..

twotwo typestypes ofof cellscells formform thisthis epitheliumepithelium talltall columnarcolumnar andand shortshort polyhedralpolyhedraltwotwo typestypes ofof cellscells formform thisthis epithelium,epithelium, talltall columnarcolumnar andand shortshort polyhedralpolyhedral..

HasHas twotwo characteristicscharacteristics whichwhich distinguishdistinguish itit fromfrom truetrue stratifiedstratified epitheliaepithelia–– itsits individualindividual cellscells exhibitexhibit polaritypolarityxx p yp y

–– ciliacilia nevernever presentpresent onon stratifiedstratified epitheliaepithelia

isis foundfound toto lineline thethe tracheatrachea bronchibronchi andand nasalnasal cavitycavityisis foundfound toto lineline thethe trachea,trachea, bronchi,bronchi, andand nasalnasal cavitycavity..

lineslines alsoalso thethe epididymisepididymis andand ductusductus (vas)(vas) deferensdeferens withwitht r iliat r iliastereociliastereocilia..

Epithelial TissuesEpithelial TissuesEpithelial TissuesEpithelial Tissues

StratifiedStratified epitheliaepithelia::StratifiedStratified epitheliaepithelia::consistingconsisting ofof twotwo oror moremore layerslayers ofof cellscells..

havehave mainlymainly aa protectiveprotective functionfunctionhavehave mainlymainly aa protectiveprotective functionfunction..

areare poorlypoorly suitedsuited forfor thethe functionfunction ofof absorptionabsorption andand secretionsecretion becausebecauseofof theirtheir thicknessthickness (some(some maymay bebe areare moderatelymoderately permeablepermeable toto waterwater andandofof theirtheir thicknessthickness (some(some maymay bebe areare moderatelymoderately permeablepermeable toto waterwater andandsmallsmall molecules)molecules)..

TheThe degreedegree ofof stratificationstratification isis relatedrelated toto thethe kindskinds ofof physicalphysical stressesstresses totowhichwhich thethe surfacesurface isis exposedexposed..

classificationclassification isis basedbased onon thethe shapeshape ofof andand structurestructure ofof thethe surfacesurface cellscellsllll ff hh b lb l ll llll b d lb d l hhsincesince cellscells ofof thethe basalbasal layerlayer areare usuallyusually cuboidalcuboidal inin shapeshape..

StratifiedStratified squamoussquamous epitheliumepitheliumvariablevariable numbernumber ofof cellcell layerslayers whichwhich exhibitexhibit transitiontransition fromfrom aa cuboidalcuboidalvariablevariable numbernumber ofof cellcell layers,layers, whichwhich exhibitexhibit transitiontransition fromfrom aa cuboidalcuboidalbasalbasal layerlayer toto aa flattenedflattened surfacesurface layerlayer..basalbasal cellscells dividedivide continuouslycontinuously toto replacereplace thethe surfacesurface sheddingshedding cellscells..yy pp ff ggisis wellwell adaptedadapted toto withstandwithstand abrasionabrasion..lineslines thethe oraloral cavity,cavity, pharynx,pharynx, esophagus,esophagus, analanal canal,canal, uterineuterine cervixcervix andand

h hh h bb h lh l bb bb h hh h kkvagina,vagina, sitessites whichwhich areare subjectsubject toto mechanicalmechanical abrasionabrasion butbut whichwhich areare keptkeptmoistmoist byby glandularglandular secretionssecretions..

StratifiedStratified squamoussquamous keratinizedkeratinized epitheliumepitheliumThiThi i li di li d tt ff thth id iid i ff thth kiki dd ii d t dd t d ttThisThis specializedspecialized typetype formsforms thethe epidermisepidermis ofof thethe skinskin andand isis adaptedadapted totowithstandwithstand thethe constantconstant abrasionabrasion andand desiccationdesiccation toto whichwhich thethe bodybody surfacesurfaceisis exposedexposed.. TheThe surfacesurface layerslayers areare nonnon--vitalvital andand formform keratinkeratin containerscontainers..xpxp ff yy ff kk

Epithelial TissuesEpithelial TissuesStratifiedStratified cuboidalcuboidal epitheliumepitheliumisis thin,thin, usuallyusually consistconsist ofof onlyonly twotwo oror threethree layerslayers ofof cuboidalcuboidal oror lowlowisis thin,thin, usuallyusually consistconsist ofof onlyonly twotwo oo th eeth ee laye slaye s ofof cuboidalcuboidal oo lowlowcolumnarcolumnar cellscells..

isis usuallyusually confinedconfined toto thethe lininglining ofof thethe largelarge excretoryexcretory ductsducts ofof exocrineexocrineglandsglands (( likelike:: salivarysalivary glandsglands && sweatsweat glands)glands)..

itit isis probablyprobably notnot involvedinvolved inin significantsignificant absorptiveabsorptive oror secretorysecretory activityactivitybb ll dd ll hh ldld bb ff d dff d d bb llbutbut merelymerely providesprovides aa moremore strongstrong lininglining thanthan wouldwould bebe affordedafforded byby simplesimpleepitheliumepithelium..

St tifi dSt tifi d ll ith liith liStratifiedStratified columnarcolumnar epitheliumepitheliumitit isis relativelyrelatively rarerare.. BasalBasal layerlayer isis polyhedralpolyhedral cells,cells, surfacesurface layerlayer columnarcolumnarcellscellscellscells..

lineslines conjunctivaconjunctiva andand partpart ofof malemale urethraurethra..

TransitionalTransitional epitheliumepithelium (Stratified)(Stratified)exclusivelyexclusively lineslines thethe urinaryurinary tracttract whichwhich highlyhighly specializedspecialized toto accommodateaccommodateexclusivelyexclusively lineslines thethe urinaryurinary tract,tract, whichwhich highlyhighly specializedspecialized toto accommodateaccommodateaa greatgreat degreedegree ofof stretchstretch && toto withstandwithstand thethe toxicitytoxicity ofof urineurine..ItIt hashas somesome featuresfeatures ofof stratifiedstratified cuboidalcuboidal && stratifiedstratified squamoussquamous epitheliumepitheliumff ff ff ff qq pp44 toto 55 layerslayers inin relaxedrelaxed statestate;; basalbasal cellscells areare cuboidal,cuboidal, intermediateintermediate cellscells arearepolyhedral,polyhedral, andand surfacesurface cellscells areare large,large, roundedrounded && maymay bebe binucleatebinucleate..

ll h dh d hh dd && ff ll22 oror 33 layerslayers inin stretchedstretched statestate;; thethe intermediateintermediate && surfacesurface layerslayers areareextremelyextremely flattenedflattened..

Epithelial TissuesEpithelial TissuesSpecializationSpecialization ofof epithelialepithelial cellcell surfacessurfaces

FreeFree surfacessurfaces (luminal)(luminal) ofof epithelialepithelial cellscells maymay showshow threethree mainmaintypestypes ofof specialization,specialization, microvilli,microvilli, ciliacilia andand stereociliastereocilia..

LateralLateral surfacessurfaces (intercellular)(intercellular) ofof epithelialepithelial cellscells areare linkedlinked bybyseveralseveral differentdifferent typestypes ofof membranemembrane andand cytoskeletalcytoskeletalspecialization,specialization, whichwhich contributecontribute toto communicationcommunication andand coco--operationoperation betweenbetween cellscells toto achieveachieve thethe functionsfunctions ofof epitheliumepithelium..

BasalBasal surfacessurfaces ofof epithelialepithelial cellscells showshow threethree typestypes ofofspecialization,specialization, basementbasement membrane,membrane, hemidesmosomeshemidesmosomes andand basalbasalinfoldingsinfoldings..

MicrovilliMicrovilli areare minuteminute fingerfinger--likelike projectionsprojections ofof thethe luminalluminalll bb f df d ii i h lii h li i l li l l hhplasmaplasma membranemembrane foundfound inin manymany epitheliaepithelia particularlyparticularly thosethose

specializedspecialized forfor absorptionabsorption..

TheseThese projectionsprojections maymay increaseincreasethethe surfacesurface areaarea moremore thanthan 3030tititimestimes..

MicrovilliMicrovilli areare aboutabout 00..55--11..00µµmm inin lengthlength..µµmm inin lengthlength..

EpithelialEpithelial cellcell maymay havehave upup toto30003000 microvillimicrovilli..

TheThe cytoplasmiccytoplasmic corecore ofof eacheachmicrovillusmicrovillus containscontains finefineproteinprotein filamentsfilaments whichwhich insertinsertintointo thethe terminalterminal web,web, thatthatformform partpart ofof cytoskeletoncytoskeletonformform partpart ofof cytoskeletoncytoskeleton..

CiliaCilia areare motilemotile structuresstructures whichwhich projectproject inin parallelparallel rowsrows fromfromh l lh l l l ll l ff llllcertaincertain epithelialepithelial luminalluminal surfaces,surfaces, especiallyespecially inin respiratoryrespiratory tractstracts

andand oviductsoviducts..

CiliaCilia areare aboutabout 55--1010 µµmm ininl thl th dd 00 22 ii di tdi tlengthlength andand 00..22 µµmm inin diameterdiameter..

EpithelialEpithelial cellcell maymay havehave upup toto300300 ciliacilia usuallyusually ofof samesame300300 ciliacilia usuallyusually ofof samesamelengthlength..

EachEach ciliumcilium isis boundedbounded byby aayyplasmaplasma membranemembrane..

CiliumCilium containscontains aa centralcentral corecorecalledcalled thethe axonemeaxoneme consistingconsistingofof aa centralcentral twotwo microtubulesmicrotubulessurroundedsurrounded byby ninenine peripheralperipheralsurroundedsurrounded byby ninenine peripheralperipheraldoubletsdoublets..

TheThe axoneme,axoneme, atat itsits base,base,x ,x , ,,insertsinserts intointo aa basalbasal bodybody..

CiliaCilia beatbeat withwith aa wavewave--likelikesynchronoussynchronous rhythmrhythm propellingpropelling

ff f lf l ff fl dfl dsurfacesurface filmsfilms ofof mucusmucus oror fluidfluidinin aa consistentconsistent directiondirection overoverthethe epithelialepithelial surfacesurface..thethe epithelialepithelial surfacesurface..

ActionAction ofof ciliacilia resultsresults fromfromlongitudinallongitudinal movementmovement ofof thethegg ffdoubletsdoublets..

EnergyEnergy forfor thethe movementmovement ofofciliacilia isis providedprovided byby subjacentsubjacentmitochondriamitochondria inin thethe formform ofofATPATPATPATP..

StereociliaStereocilia areare veryvery longlong microvillimicrovilli foundfound inin smallsmall numbernumber inind dd d dd dd d fd f U llU ll hh hh hh ff ff llepididymisepididymis andand ductusductus deferensdeferens.. UsuallyUsually theythey havehave thethe formform ofof ciliacilia

butbut dodo notnot havehave microtubulesmicrotubules andand containcontain filamentousfilamentous skeletonskeleton..

Junctional complexJunctional complex

TightTight junctionsjunctions “Zonulae“Zonulaeoccludens”occludens”occludensoccludens*They*They locatelocate immediatelyimmediately underunderthethe luminalluminal surfacesurface ofofthethe luminalluminal surfacesurface ofofepitheliumepithelium..

**They**They sealseal thethe intercellularintercellularyyspacesspaces soso thatthat luminalluminal contentscontentscannotcannot penetratepenetrate betweenbetween thetheli ili i lllllininglining cellscells..

***Each***Each tighttight junctionjunction formsforms aacontinuouscontinuous circumferentialcircumferential bandbandcontinuouscontinuous circumferentialcircumferential bandbandoror zonulezonule aroundaround thethe cellcell..

Junctional complexJunctional complex

AdheringAdhering junctionsjunctions

TheyThey tightlytightly bindbind thethe constituentconstituentcellscells ofof thethe epitheliumepithelium togethertogether andand

hh ff hhactact asas anchoringanchoring sitessites forfor thethecytoskeletoncytoskeleton ofof eacheach cellcell..

TheyThey areare ofof twotwo morphologicalmorphologicalTheyThey areare ofof twotwo morphologicalmorphologicaltypestypes::

ZonulaZonula adherensadherens thatthat formsforms aaZonulaZonula adherensadherens thatthat formsforms aacontinuouscontinuous bandband aroundaround thethe cellcellprovidingproviding structuralstructural reinforcementreinforcementtoto thethe occludingoccluding junctionjunction..

Junctional complexJunctional complex

MaculaMacula adherensadherens oror DesmosomesDesmosomesareare circumferentiallycircumferentially arrangedarrangedaroundaround thethe columnarcolumnar cellcell deepdeep totothethe continuouscontinuous adheringadhering junctionjunctioninin thethe formform ofof smallsmall circularcircularinin thethe formform ofof smallsmall circularcircularpatchespatches oror spotsspots..

LargerLarger desmosomesdesmosomes areare alsoalso widelywidelygg yyscatteredscattered overover thethe intercellularintercellularsurfacessurfaces ofof allall epithelialepithelial cellscells..

DesmosomesDesmosomes numbernumber areare greatestgreatestinin stratifiedstratified squamoussquamous epitheliaepitheliaprovidingproviding structuralstructural integrityintegrity atatprovidingproviding structuralstructural integrityintegrity atatsurfacessurfaces subjectsubject toto stressstress (friction)(friction)..

CommunicatingCommunicating junctionsjunctions areare broadbroad patchespatches wherewhere adjacentadjacentplasmaplasma membranesmembranes areare closelyclosely opposedopposed leavingleaving aa narrownarrow interveninginterveningplasmaplasma membranesmembranes areare closelyclosely opposedopposed leavingleaving aa narrownarrow interveninginterveninggapgap (named(named gapgap junction)junction)..

EachEach gapgap junctionjunction containscontains numerousnumerous porespores whichwhich permitpermit thethe passagepassage ofofpositivelypositively chargedcharged ionsions andand otherother smallsmall moleculesmolecules (>(>22nm)nm) fromfrom oneone cellcell totoanotheranother..

EachEach porepore consistsconsists ofof aa minuteminute tubulartubular structurestructure calledcalled connexonconnexon whichwhichtraversestraverses thethe intercellularintercellular gapgap.. TheThe connexonconnexon consistsconsists ofof twotwo ringring--likelikecylinders,cylinders, oneone penetratingpenetrating eacheach ofof thethe opposingopposing cellcell membranemembrane.. EachEachcylindercylinder isis mademade upup ofof sixsix transmembranetransmembrane proteinprotein moleculesmolecules..

bb h lh lGapGap junctionsjunctions areare moremore numerousnumerous inin embryonicembryonic epitheliaepithelia..

TheyThey areare alsoalso probablyprobably involvedinvolved inin thethe passagepassage ofof nutrientsnutrients fromfrom cellscells deepdeepii hh i h lii h li llll ff ff hh i i li i l llinin thethe epitheliumepithelium toto cellscells moremore farfar fromfrom thethe nutritionalnutritional supplysupply..

GapGap junctionsjunctions alsoalso provideprovide thethe meansmeans ofof electricalelectrical couplingcoupling ofof visceralvisceral andanddidi ll llll ittiitti hh t tit ticardiaccardiac musclemuscle cellscells permittingpermitting synchronoussynchronous contractioncontraction..

BasementBasement membranes,membranes, ofof variablevariable thickness,thickness, separateseparate epitheliaepitheliafromfrom underliningunderlining supportingsupporting tissuestissues andand areare nevernever penetratedpenetrated bybybloodblood vesselsvessels.. Thus,Thus, epitheliaepithelia areare dependentdependent onon thethe diffusiondiffusion ofof

dd b lb l ff ddoxygenoxygen andand metabolitesmetabolites fromfrom adjacentadjacent supportingsupporting tissuestissues.. ItIt isis nonnon--cellularcellular structurestructure composedcomposed ofof basalbasal laminalamina andand reticularreticular laminalamina

dd bb ithith li htli ht iiandand cancan bebe seenseen withwith lightlight microscopemicroscope..

WithWith thethe electronelectron microscope,microscope, thethe basementbasement membranemembrane appearsappears asasthreethree layerslayers:: laminalamina lucidalucida ((2020--5050 nm)nm) andand laminalamina densadensa ((2020--300300nm)nm) (together(together basalbasal lamina)lamina) ;; andand thethe laminalamina fibroreticularisfibroreticularis whichwhich

hh hh d ld lmergesmerges withwith thethe underlyingunderlying connectiveconnective tissuetissue..

HemidesmosomesHemidesmosomes (half(half desmosomes)desmosomes) areare presentpresent onon thethe innerinneraspectaspect ofof thethe basalbasal plasmaplasma membranemembrane providingproviding anchorageanchorage ofof thetheaspectaspect ofof thethe basalbasal plasmaplasma membranemembrane providingproviding anchorageanchorage ofof thethecytoskeletoncytoskeleton toto thethe basementbasement membranemembrane andand underlingunderling tissuestissues..

BasalBasal infoldingsinfoldings areare foldsfolds inin basalbasal membranemembrane ofof somesome cellscells(kidney(kidney tubulestubules && striatedstriated ductsducts ofof salivarysalivary glands)glands) toto increaseincrease thethe(kidney(kidney tubulestubules && striatedstriated ductsducts ofof salivarysalivary glands)glands) toto increaseincrease thethecellcell surfacesurface forfor passagepassage ofof absorbedabsorbed fluidfluid andand ionsions fromfromsurroundingsurrounding capillarycapillarysurroundingsurrounding capillarycapillary..

Epithelial TissuesEpithelial TissuesGlandularGlandular epithelialepithelial tissuestissues

f df d bb llll i li di li d dd iiareare formedformed byby cellscells specializedspecialized toto produceproduce secretionsecretion..

cellscells maymay synthesize,synthesize, store,store, andand secretesecrete proteins,proteins, lipids,lipids, ……..

cancan bebe classifiedclassified accordingaccording toto differentdifferent criteriacriteria..

maymay consistconsist ofof isolatedisolated cellscells “unicellular”“unicellular” oror areare composedcomposed ofofyy ff ffclustercluster ofof cellscells “multicellular”“multicellular”..

alwaysalways arisearise fromfrom surfacesurface epitheliumepithelium byby cellcell proliferationproliferation andandyy ff ff pp yy p fp finvasioninvasion ofof subjacentsubjacent connectiveconnective tissue,tissue, followedfollowed bybydifferentiationdifferentiation..ffff

existexist intointo twotwo typestypes:: endocrineendocrine (ductless)(ductless) andand exocrineexocrine..

Goblet cellsGoblet cells

AreAre modifiedmodified columnarcolumnar cellscellsscatteredscattered amongstamongst thethe cellcell ofofgg ffmanymany simplesimple epithelia,epithelia, whichwhichsynthesissynthesis andand secretesecrete mucusmucus..

NamedNamed forfor theirtheir resemblanceresemblance totodrinkingdrinking gobletsgoblets..

MM hh i ti t ff f tif tiMucusMucus hashas aa varietyvariety ofof functionsfunctions..InIn respiratoryrespiratory tracttract itit protectsprotectsfromfrom drying,drying, actsacts asas traptrap forfor finefineff y g,y g, pp ff ffparticlesparticles && microorganismsmicroorganisms.. InInupperupper gastrointestinalgastrointestinal protectsprotectsff di idi i dd ii ll iifromfrom autodigestionautodigestion andand inin lowerlower ititlubricateslubricates thethe passagepassage ofof fecesfeces..

ExocrineExocrine glandsglandsExocrineExocrine glandsglands dischargedischarge theirtheir secretorysecretory productproduct viavia aa ductduct ontoonto epithelialepithelialsurfacesurface.. TheyThey maymay bebe classifiedclassified accordingaccording toto twotwo majormajor characteristicscharacteristics::

ThTh h lh l ff hh l dl d ii l dl d bb di id ddi id d ii i li lTheThe morphologymorphology ofof thethe glandgland.. ExocrineExocrine glandsglands maymay bebe divideddivided intointo simplesimpleandand compoundcompound accordingaccording toto structurestructure ofof theirtheir duct,duct, andand inin tubulartubular andandacinaracinar inin relationshiprelationship toto theirtheir secretorysecretory portionportion..acinaracinar inin relationshiprelationship toto theirtheir secretorysecretory portionportion..

TheThe meansmeans ofof dischargedischarge ofof secretionssecretions.. ThisThis occursoccurs inin threethree waysways::

MerocrineMerocrine “eccrine”“eccrine” involvesinvolves thethe processprocess ofof exocytosisexocytosis && isis thethe mostmostpp ff x yx ycommoncommon formform ofof secretionsecretion (e(e..gg.. proteins)proteins)..

ApocrineApocrine involvesinvolves thethe dischargedischarge ofof free,free, unbroken,unbroken, membranemembrane--boundboundvesicles,vesicles, thisthis isis anan unusualunusual modemode ofof secretionsecretion appliesapplies toto lipidlipid secretionsecretion“breasts“breasts && somesome sweatsweat glands”glands”..

H l iH l i i li l di hdi h ff h lh l llll i hi h bbHolocrineHolocrine involvesinvolves dischargedischarge ofof wholewhole secretorysecretory cellscells withwith subsequentsubsequentdisintegrationdisintegration ofof thethe cellscells toto releaserelease thethe secretionsecretion “sebaceous“sebaceous glands”glands”..

SimpleSimple tubulartubular glandsglands SimpleSimple coiledcoiled tubulartubular glandsglands

LargeLarge intestineintestine SweatSweat glandsglands

Simple acinarSimple acinarPenile urethraPenile urethraPenile urethraPenile urethra

SimpleSimple branchedbranched tubulartubular SimpleSimple branchedbranched acinaracinar

StomachStomach SebaceousSebaceous glandsglands

CompoundCompound tubulartubular glandsglands CompoundCompound acinaracinar glandsglands

Brunner’sBrunner’s glandsglands PancreasPancreas

Compound tubuloCompound tubulo--acinaracinarSubmandibular salivary glandsSubmandibular salivary glandsSubmandibular salivary glandsSubmandibular salivary glands

Endocrine glands Endocrine glands

TThey are ductless glands.hey are ductless glands.

The secretory product diffusing directly into the bloodstream. The secretory product diffusing directly into the bloodstream. The secretory product diffusing directly into the bloodstream. The secretory product diffusing directly into the bloodstream.

Secretions are hormones which control the activity of cells & Secretions are hormones which control the activity of cells & tissues usually far removed from the site of secretiontissues usually far removed from the site of secretiontissues usually far removed from the site of secretion.tissues usually far removed from the site of secretion.

They are of two types:They are of two types:

M t d i l d i t f l d f t M t d i l d i t f l d f t Most endocrine glands consist of clumps or cords of secretory Most endocrine glands consist of clumps or cords of secretory cells surrounded by a rich network of small blood vessels (e.g. cells surrounded by a rich network of small blood vessels (e.g. pituitary gland)pituitary gland)pituitary gland).pituitary gland).

Follicular endocrine glands consist of spheroidal cavities Follicular endocrine glands consist of spheroidal cavities l d b th t ll th it ll d f lli l l d b th t ll th it ll d f lli l enclosed by the secretory cells; these units are called follicles enclosed by the secretory cells; these units are called follicles

(e.g. thyroid gland).(e.g. thyroid gland).