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APICAL SURFACE MODIFICATIONS OF THE CELL

APICAL SURFACE MODIFICATIONS OF THE CELL. Prof.Dr .Meltem ÖZGÜNER Department of Histology Embryology. TISSUES. Epithelial Tissue Connective Tissue Muscle Tissue Nervous Tissue. TISSUES. Epithelial Tissue Covers body surfaces , lines body cavities , and form glands. TISSUES.

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APICAL SURFACE MODIFICATIONS OF THE CELL

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  1. APICAL SURFACE MODIFICATIONS OF THE CELL Prof.Dr.Meltem ÖZGÜNER Department of HistologyEmbryology

  2. TISSUES • EpithelialTissue • ConnectiveTissue • MuscleTissue • NervousTissue

  3. TISSUES • EpithelialTissue • Covers body surfaces, lines body cavities, and form glands

  4. TISSUES • ConnectiveTissue • Underliesorsupportstheotherthreebasictissues, bothstructurallyandfunctionally

  5. ConnectiveTissue

  6. TISSUES • MuscleTissue • Madeup of contractilecellsand is responsibleformovement

  7. TISSUES • NervousTissue • Receives, transmitsandintegratesinformationfromoutsideand inside the body tocontroltheactivities of the body.

  8. EPITHELIAL TISSUE • Thecellsmakeupepitheliumhavethreeprincipalcharacteristics: 1-Theyarecloselyapposedandadheretooneanotherbymeans of specificcell-to-celladhesionmoleculesthat form specializedcelljunctions.

  9. EPITHELIAL TISSUE 2-Theyexhibitfunctionalandmorphologicpolarity • A freesurfaceorapical domain • A lateral domain • Abasal domain

  10. EPITHELIAL TISSUE 3-Theirbasalsurface is attachedto an underlyingbasementmembrane, (a noncellular, protein-polysaccharide-richlayer)

  11. EPITHELIAL TISSUE • CELL POLARITY • Epithelialcellsexhibitdistinctpolarity. • Theyhave an apical domain, a lateral domain, andabasal domain. • Specificbiochemicalcharacteristicsareassociatedwitheachcellsurface. • Thesecharacteristicsandgeometricarrangements of thecellsdeterminethefunctionalpolarity of allthreecelldomains.

  12. EPITHELIAL TISSUE • Thefreeorapical domain is alwaysdirectedtowardtheexteriorsurfaceorthelumen of an enclosedcavityortube.

  13. THE APICAL DOMAIN AND ITS MODIFICATIONS • Theapical domain, theregion of theepithelialcellfacingthelumen, is rich in ionchannels, carrierproteins, H+ ATPase, glycoproteins, andhydrolyticenzymes • It is alsothe site whereregulatedsecretoryproductsaredeliveredforrelease.

  14. THE APICAL DOMAIN AND ITS MODIFICATIONS • Inmanyepithelialcells, theapical domain exhibitsspecialstructuralsurfacemodificationstocarryoutspecificfunctions.

  15. THE APICAL DOMAIN AND ITS MODIFICATIONS Thestructuralsurfacemodificationsinclude; -Microvilli -Stereoclia (stereovilli) -Cilia

  16. MICROVILLI • Microvilliarefingerlikecytoplasmicprojections on theapicalsurface of mostepithelialcells. • As observed in electronmicroscope (EM), microvillivarywidely in appearance.

  17. MICROVILLI • Insomecelltypes, microvilliareshort, irregular, bleblikeprojections. • Inothercelltypes, theyaretall, closelypacked, uniformprojectionsthatincreasethefreecellsurfacearea.

  18. MICROVILLI • Thenumberandshape of themicrovilli of a givencelltypecorrelatewithitsabsortivecapacity.

  19. MICROVILLI Amongthefluidtransportingepithelia, e.g., • epithelium of intestineand • epithelium of kidneytubule, a distinctiveborder of verticalstriations at theapicalsurface of thecell, representingthemicrovilli, is easilyseen in thelightmicroscope.

  20. MICROVILLI • Inintestinalabsortivecellsthissurfacestructure (consistsmicrovilli) is calledthestriatedborder • Inthekidneytubulecells,it is calledbrushborder

  21. MICROVILLI • Themicrovilli of theintestinalepithelium (striatedborder) arethemosthighlyorderedareevenmoreuniform in appearancethanthosethatconstitutethebrushborder of kidneycells.

  22. MICROVILLI • Withinthemicrovillithereareclusters of actinfilaments (microfilaments). • Actinfilamentsareanchoredtovillinlocated in the tip of themicrovillusandextenddownintotheapicalcytoplasm.

  23. MICROVILLI • Microvilli are apical extensions of the cell that are filled with actin. • An extracellular coat (glycocalyx) is bound to the plasmalemma of the microvilli. • The terminal web is a network that contains actin filaments, intermediate filaments and spectrin.

  24. MICROVILLI • Cross sectioned microvilli in apical region of cell of intestinal lining showing cores of actin. • The outsides of the microvilli are covered with a glycocalyx (cell coat).

  25. MICROVILLI • Actinfilaments of themicrovilliinteractwith a horizontal network of actinfilaments, the terminal web.

  26. MICROVILLI • Terminal web, liesjustbelowthebase of themicrovilli. • The terminal web is composed of actinfilamentsstabilizedbyspectrin , whichalsoanchorsthe terminal web totheapicalcellmembrane.

  27. MICROVILLI • The presence of myosin II andtropomyosin in the terminal web explainsitscontractileability.

  28. MICROVILLI • Theactinfilaments inside themicrovillusarecross-linked at 10-nmintervalsbytheactin-bundlingproteinsfascinandfimbrin. • Thiscross-linkageprovidessupportandgivesrigiditytothemicrovilli.

  29. MICROVILLI

  30. STEREOCILIA • Stereociliaareunusuallylong, immotilemicrovilli • Theyarelong, nonmotileprocesses of cells of theepididymisandductusdeferensandthesensory (hair) cells of theear.thatareactuallylongerbranchedmicrovilliandshould not be confusedwithtruecilia. • Inepididymisand D.deferens- absorptivefunction • Insensorycells of theear- sensoryreceptorfunction

  31. STEREOCILIA • Likemicrovilli, stereociliaaresupportedbyinternalactinfilamentbundlesthatarecross-linkedbyfimbrin. • Unlikemicrovilli, erzinanchorstheactinfilamentstotheplasmamembrane of stereocilia.

  32. STEREOCILIA • Stereocilia of thesensoryepithelium of theearareuniform in structureandpossess an internalstructuresimilartothat of genitalductstereocilia. • Howevertheylackbotherzinandα-actin.

  33. STEREOCILIA

  34. CILIA & FLAGELLA • Ciliaareelongated, motilestructureson thesurface of someepithelialcells. • 5-10 µm longand 0.2 µm in diameter.

  35. CILIA & FLAGELLA • Theyaresurroundedbythecellmembraneandcontain a centralpairof isolatedmicrotubulessurroundedby9 morepairsof microtubules. • (Axoneme)

  36. CILIA & FLAGELLA • Ciliaareinsertedintobasalbodies, whichareelectron dense structures at theapicalpolejustbelowthecellmembrane

  37. CILIA & FLAGELLA

  38. CILIA & FLAGELLA • TheA microtubuleis composed of 13 tubulinprotofilaments, arranged in side-by-sideconfiguration, whereastheB microtubuleis composed of 10 tubulinprotofilaments.

  39. CILIA & FLAGELLA • Incrosssection, eachdoubletexhibits a pair of armsthatcontainciliarydynein, a microtubuleassociated protein

  40. CILIA & FLAGELLA • Thetwocentralmicrotubulesareseperated but arepartiallyenclosedby a centralsheatprojections at 14 nmintervalsalongthelength of thecilium.

  41. CILIA & FLAGELLA • Radialspokesextendfromeach of the nine doubletstowardthetwocentralmicrotubules • Theproteinsformingradialspokesandthenexinconnectionsbetweentheouterdoubletsmakelargeamplitudeoscillations of theciliapossible.

  42. CILIA & FLAGELLA • Thetwocentralmicrotubules of theciliumend at thelevel of the top of thebasal body.. • Crosssection of thebasal body reveal nine circularyarrangedmicrotubuletriplets but not thetwocentralsinglemicrotubules of thecilium.

  43. CILIA & FLAGELLA • Basalbodieshave a structureanalogoustothat of thecentrioles.

  44. CILIA & FLAGELLA • Inlivingcells, ciliahave a rapidbackandforthmovement.

  45. CILIA & FLAGELLA • Inmostciliatedepithelia, such as thetrachea, bronchi, oroviducts, cellsmayhave as many as severalhundredcilia.

  46. CILIA & FLAGELLA • Inthetrachea, theciliasweepmucusandtrappedparticlestowardtheoropharynxwhere it is swallowedwithsalivaandeliminatedfromthe body. • Intheoviducts, ciliahelp transport ova andfluidtowarstheuterus.

  47. FLAGELLA • Theonlycells in thehuman body thatpossessflagellaarethespermatozoa.

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