epithelium - general histology dds6214 · pdf fileepithelium lecture outline • func.on...

EpitheliumKris.neKra1s,M.D.

EpitheliumLectureObjec.ves

•  Describethestructuralandfunc.onalrela.onshipbetween:•  epitheliumandconnec.ve.ssue,and•  epitheliumandbasallamina.

•  Describethestructuralandfunc.onalfeaturesofepithelialintercellularjunc.onsandspecializa.onsoftheapicalsurfaceofepithelialcells.

MoreEpitheliumLectureObjec.ves

•  Describethestructuralandfunc.onaldiversityofepithelium.

•  Describetheclassifica.onsystemofcovering/liningepithelium.

•  Describethehistologicfeaturesofglandularepithelium.

EpitheliumLectureOutline

•  Func.onandtypesofepithelium

•  Structureofepithelium

•  Typesofcovering/liningepithelium

•  Typesofglandularepithelium

Func.onsofEpithelium

•  Coveringofexternalsurfaces•  Liningofinternalsurfaces•  Protec.on•  Absorp.on•  Secre.on•  Sensa.on•  Contrac.on

TwoMainKindsofEpithelium

CoveringandliningepitheliumCoversoutersurfacesofbodyandlinesinternalbodypassages

GlandularepitheliumContainscellsspecializedforsecre.on

UniqueCharacteris.csofEpithelium

•  Basallaminaanchorsepitheliumtounderlyingconnec.ve.ssue.

•  Epithelialcellsareverycohesiveduetointercellularjunc.ons.

•  Epithelialcellsvaryalotinshapeandsize.

•  Epithelial.ssuesareavascular.

•  Epithelialcellsdemonstratepolarity.



•  Structureofepithelium•  Basementmembrane•  Connec.onsbetweencells•  Specializedapicalstructures



•  Structureofepithelium•  Basementmembrane

BasementmembraneEpithelialcells

Basementmembrane=BasalLamina+Re.cularLamina

Basementmembrane

Epithelium

Basallamina

Re.cularlamina

Basallamina

Re.cularlamina

Anchoringfibrils(typeVIIcollagen)

Anchoringplaques(typeIVcollagen)

Re.cularfibers(typeIIIcollagen)

Epithelialcell

TypeIVcollagenandperlecan

(aproteoglycan)

Laminin(aglycoprotein)

laminalucida

laminadensa

Composi.onofBasalLaminaandRe.cularLamina

Func.onsofBasalLamina

•  Structure:aXachesepitheliumtoconnec.ve.ssue

•  Organiza.on:arrangesplasmamembraneproteinsinthebasalmembrane

•  Filtra.on:regulatesmovementofmaterialbetweenepitheliumandconnec.ve.ssue

Don’tmakethismistake!

“Basallamina”and“basementmembrane”aresome.mesusedinterchangeably.

Thisiswrong,wrong,wrong!

Thebasallaminaispartofthebasementmembrane.Theyarenotthesamething.



•  Structureofepithelium•  Basementmembrane•  Intercellularjunc.ons

Intercellularjunc.onsconnectepithelialcells

Intercellularjunc.onsarepresentinmost.ssuesbutareespeciallynumerousandprominentinepithelium.

•  Zonulaoccludens(.ghtjunc.on)

•  Zonulaadherens(beltdesmosome)

•  Maculaadherens(desmosome)

•  Hemidesmosomes

•  Gapjunc.on(nexus)

IntercellularJunc.ons

Intercellularjunc.ons

(Zonulaadherens)

(Zonulaoccludens)

Zonaoccludens(.ghtjunc.on)

•  Mostapicaljunc.oninepithelium

•  Formbands(zonula)thatcompletelyencircleeachcell

•  Membranesofadjacentcellsfusetosealofftheintercellularspace

Zonaoccludens(.ghtjunc.on)

•  Claudinsandoccludinsaretwofamiliesofproteinsthatformasealtopreventflowofmaterialsbetweenepithelialcells

•  Morezonaoccludens=.ghterseal

Zonulaadherens(beltdesmosome)

•  Formbandsthatcompletelyencircleeachcell

•  Cadherinandcateninproteinsprovideadhesionbetweenadjacentcells

•  Ac.nfilamentsincytoplasminsertintoaXachmentplaques

Maculaadherens(spotdesmosome)

•  Spotadhesionbetweencells

•  Desmosomesonadjacentcellslineup

•  Cadherinspresentinintercellularspace


•  Cytokera.nintermediatefilamentsinsertintoaXachmentplaquescontainingdesmoplakinandplakoglobin

•  SuperstrongaXachmentpointsbetweencells

•  Themoredesmosomes,themore.ghtlytheepithelialcellsareaXached

Pemphigusvulgaris

•  Ablisteringdiseaseinwhichpa.entsmakeautoan.bodiestodesmogleinproteins

•  Epithelialcellconnec.ons(spotdesmosomes)loosen,causingfluidaccumula.onandsuperficialblisters

Cytokera.nintermediatefilaments

CytoplasmicaXachmentplaques

Plasmamembranes


Spotdesmosomesinstratumspinosumofskin

HemidesmosomesaXachepithelialcellstobasallamina.IntegrinsaXachthebasalpor.onofthecelltothebasallamina.

Hemidesmosomes

Kera.nintermediatefilamentsinepithelialcell

Hemidesmosomes

AXachmentplaque

Re.cularlamina

Bullouspemphigoid

•  Ablisteringdiseaseinwhichpa.entsmakeautoan.bodiesto“bullouspemphigoidan.gen”inhemidesmosomeaXachmentplaques

•  Epithelialcellsdetachfrombasallamina,causingfluidaccumula.onandblisterforma.on

Junc.onalcomplexofintercellularjunc.ons

•  ZO:zonulaoccludens•  ZA:zonulaadherens•  D:desmosome

•  Insometypesofepithelia(simplecolumnarofdiges.vetract)junc.onsoccurinthisorder

Gap(communica.ng)junc.on•  Occuralmostanywhere

alonglateralsurfacesofepithelialcellsandalsoinothercells,suchascardiacmusclecells

•  Connexonsareproteinchannelswithcentralporesconnec.ngplasmamembranes

•  Allowionsandothersmallmoleculestopassthroughtoadjacentcellstofacilitatecommunica.on

name

tight junction

adherens junction

desmosome junction

gap junction

hemidesmosome junction



•  Structureofepithelium•  Basementmembrane•  Intercellularjunc.ons•  Specializedapicalstructures

Microvilli

Microvilli+cellcoat(orglyocalyx)=brushborderorstriatedborder

Purposeofmicrovilli:increasesurfaceareaforabsorp.onorsecre.on

Microvillus

Tight junctions

Belt desmosome

Spot desmosome

Gap junction

Intermediate filament

Hemidesmosome

Basal lamina

Microvilli

Microvillihaveacentralcoreof

ac.nmicrofilaments

Microvillidon’twavebackandforthlikecilia.

Stereocilia

Stereociliaarelong,non-mo.lemicrovilli

foundinpartsofthemalereproduc.vesystem

Stereocilia

Spermatozoa

CiliaCiliaaremuchlongerandwiderthanmicrovilli.

Theymovebackandforthtopropelfluidalongtheepithelialsurface.

Ciliaonrespiratoryepithelialcells

CiliaCiliacontainmicrotubulesina9+2configura.oncalledan“axoneme”

2centralmicrotubulessurroundedby9pairsofmicrotubules

Ciliainsertintobasalbodieswith9tripletsofmicrotubules

Howiscovering/liningepitheliumcategorized?

Shapeofsuperficialcells

Numberofcelllayers

Presenceofspecializedstructures


Shapeofsuperficialcells•  Squamous:width>height(flaXened)•  Cuboidal:width=height(square,round)•  Columnar:width<height(tallandslender)

Epithelialcellshavedifferentshapes

squamouscellsareflat cuboidalcellsarecuteandboxy

columnarcellsaretallandregal



Numberofcelllayers•  Simple:onelayerofcells•  Stra.fied:twoormorelayersofcells•  Pseudostra.fied:allcellscontactbasallamina,butnotallcellsreachlumen

Simpleepithelium:onelayerofcells

Simplesquamousepithelium Simplecuboidalepithelium

Simpleciliatedcolumnarepithelium

Endotheliumissimplesquamousepithelium.Itlinesbloodandlympha.cvessels.

SimpleSquamousEpithelium

FlaXenedsquamouscellsinasinglelayer

Mesotheliumissimplesquamousepithelium.Itlinesserouscavi.es(pleura,pericardium,peritoneum).

SimpleSquamousEpithelium

FlaXenedsquamouscellsinasinglelayer

Ductliningso1enhavesimplecuboidalepithelium,likethissmallishductinthepancreas.

SimpleCuboidalEpithelium

Cuboidalcells

inonecutelayer

Stra.fiedandpseudostra.fiedepithelium

Stra.fiedsquamousepithelium Pseudostra.fiedcolumnarepithelium

Stra.fiedSquamousEpithelium

Severallayersofsquamousepithelialcells

Mucousmembranesarecomposedofstra.fiedsquamousepithelium.

Someductsarelinedbystra.fiedcuboidalepithelium,likethislargerductinthepancreas.

Stra.fiedCuboidalEpithelium

Cuboidalcells

inafewlayers



Numberofcelllayers

Presenceofspecializedstructures•  Cilia•  Microvilli•  Kera.n

Pseudostra.fiedCiliatedColumnarEpitheliumgobletcell cilia

Respiratoryepitheliumispseudostra.fiedcolumnar,withgobletcellsandciliatedcells.

SimpleColumnarEpithelium

Theepitheliumofthesmallintes.neissimplecolumnar,withgobletcellsandabsorp.vecellswithmicrovilli.

gobletcellmicrovilli

Kera.ncoversareaswhereskinisthinbutneedsprotec.on.

Kera.nizedStra.fiedSquamousEpithelium

Squamouscells

inseverallayers

Kera.n

Areasthatarealwaysmoist(liketheesophagus)areo1enlinedbystra.fiedsquamousepitheliumwithoutalayerofkera.n.

Non-Kera.nizedStra.fiedSquamousEpithelium

Squamouscells

inseverallayers

Nokera.n!

•  Mucousgobletcell:unicellulargland

•  Exocrinegland:retainsconnec.onwithsurfaceepithelium;hormonessecretedthroughducts

•  Endocrinegland:noconnec.onwithsurfaceepithelium;hormonessecretedthroughblood

TypesofGlandularEpithelia

Forma.onofglandsfromsurfaceepithelium

Exocrinegland Endocrinegland

Secretorypor.on

Secretorypor.on

Bloodvessel

Disappearanceofductcells

•  Merocrine:secretorygranulesleavecellbyexocytosis.Mostcommonmethod.

•  Holocrine:Secretoryproductshedwithen.recell.Example:sebaceousgland

•  Apocrine:secretoryproductshedwithapicalcytoplasm.Example:mammarygland

Methodsofsecre.oninexocrineglands

•  Secretesbymerocrinemodeofsecre.on:exocytosisofproductatapicalendofcell.

•  Byfarthemostcommontypeofexocrineglandbasedonmodeofsecre.on.

Merocrinegland

•  Secre.onoccursbydisintegra.onofsecretorycells.

•  Example:sebaceousglands.

Holocrinegland

•  Secre.onoccursbylossoflargeamountofapicalcytoplasm.

•  Example:mammaryglands.

Apocrinegland

Notelossofapicalpor.onsofcytoplasm.

Mammarygland

Examplesofglandularepithelialcells

•  Iontranspor.ngcells

•  Seroussecretorycells

•  Mucoussecretorycells

•  Neuroendocrinecells

•  Myoepithelialcells

Ion-transpor.ngcells

•  Deepinvagina.onsofbasalcellmembranes

•  Zonulaoccludens

•  Mitochondriainbasalcytoplasmprovideenergyforiontransport

•  Examples:proximaltubulesinkidney

Seroussecretorycells

•  LargeroundednucleusandabundantroughER,Golgiandsecretorygranules

•  Examples:pancrea.cacinarcells,serouscellsinsalivaryglands

Seroussecretorycells

Mucoussecretorycells

•  AbundantroughER,Golgiandsecretorygranules

•  Producemucins(protec.ve,lubricantglycoproteins)

•  Examples:mucouscellsinstomach,gobletcellsinsmallandlargeintes.ne,andmucouscellsinsalivaryglands

Gobletcellsinsmallintes.ne

Mucoussecretorycells

Neuroendocrinecells

•  Densesecretorygranulesincytoplasmcontainpolypep.desand/oramines(likeepinephrineandnorepinephrine)

•  ScaXeredthroughoutthebody

Myoepithelialcells

•  Spindle-shapedcellsfoundinglandularepithelialbetweenbasallaminaandbasalcytoplasm

•  Embraceglandacinilikean“octopusonarock”

•  Containac.n:contractandsqueezeoutsecretoryproduct

epithelium - general histology dds6214 · pdf fileepithelium lecture outline • func.on...

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