Chapter41Cartilage and BoneJunmei Wang.docx
- 文档编号:14900993
- 上传时间:2023-06-28
- 格式:DOCX
- 页数:23
- 大小:28.31KB
Chapter41Cartilage and BoneJunmei Wang.docx
《Chapter41Cartilage and BoneJunmei Wang.docx》由会员分享,可在线阅读,更多相关《Chapter41Cartilage and BoneJunmei Wang.docx(23页珍藏版)》请在冰点文库上搜索。
Chapter41CartilageandBoneJunmeiWang
Chapter4CartilageandBone
Objectives
ThisChaptershouldhelpthestudentto:
~Knowthedifferencesandsimilaritiesamongthe3typesofcartilage.
~Knowthefunctionsofthe3typesofcartilageandrelatethemtotheirstructuralcharacteristicsandlocationinthebody.
~Knowthestepsinthehistogenesisandgrowthofcartilage.
~Relatetheultrastructureofthechondrocytetoitsfunctionalroleinthesynthesisandmaintenanceoftheextracellularmatrix.
~Recognizethetypeofcartilagepresentandidentifyitscomponents(eg,chondrocytes,perichondrium,capsularmatrix)inaphotomicrographorslideofatissueororgan.
Overview
I.GENERALFEATURESOFCARTILAGE.Cartitage,isaskeletalconnectivetissuecharacterizedbyfirmnessandresiliency.Itformsmostofthefetalskeletonandpersistsinlocationswhereitsmechanicalpropertiesareneeded.Mostferalcartilageeventuallybecomesbone.
A.Composition:
Likeallconnectivetissues,cartilageiscomposedofcells,fibers,andgroundsubstance.Theextracellularmatrixpredominatesanddeterminescartilage'smechanicalproperties.TypeIIcollagenisacharacteristiccartilagematrixcomponent,andtheabundantgroundsubstanceisfirmandgellike.Cartilagecellsaretermedchondrocytes.
B.VascularSupply:
Mostcartilageisenvelopedbyalayerofdensecormectivetissue,theperiechondrium,whichcontainsthevascularsupplyandfibroblastlikestemcellsfromwhichaddi-tionalchondrocytesmayarise.Fewbloodvessels(ornerves)arcfoundwithincartilage,thusthecompositionofthegroundsubstanceiscrucialtothepercolationofnutrientsandoxygentochondrocytesfromthesurroundingvessels.
C.Cells:
Underthelightmicroscope,chondrocytesaregenerallyrounded,withaneccentricnucleus,aprominentnucleolus,andbasophiliccytoplasm.WithEM,chondrocytesurfacesexhibitcharacteristicprojectionsandinfoldings.TheroughendoplasmicreticulumandGolgicomplex,arewelldeveloped;theGolgicomplexincreasesinsizeasthecellgrows,anditscisternaefillwithsecretorymaterial.Afewlipiddropletsaretypicallyfoundinthecytoplasm.ChondrocytessynthesizeandsecretethefibersandgroundsubstanceoftheextracelluIarmatrix:
collagenissynthesizedontheroughendoplasmicreticulum,andGAGsareassembledandsulfatedintheGolgicomplex.Becauseoftheirmeageroxygensupply,chondrocytesproducemuchoftheirenergybyanaerobicglycolysis.
II.THE3TYPESOFCARTILAGE.Hyalinecartilage,elasticcartilage,andfibrocartilagedifferinappearanceandmechanicalproperties,owingtodifferencesinthecompositionoftheirextracellularmatrix.Thesedifferencesarediscussedbelow.Generally,nodistinctionismadeamongthecellspresentinthedifferentcartilagetypes.
A.HyalineCartilage:
Hyalinecartilage,themostcommontypeinbothfetusandadult,iswhiteandtranslucentinthefreshstate,withafirm,gellikeconsistency.
1.Composition
a.FibersHyalinecartilagematrixischaracterizedbytypeIIcollagenintheformofthinfibrilsratherthanbundles.Theirsmallsizeandtheirrefractiveindex(closetothatofthegroundsubstance)makethemdifficulttodistinguishwiththelightmicroscope.Type11collagencontainsahigherproportionofhydroxylysinethantypeI.
b.GroundsubstanceThis,thepredominanttissuecomponent,iscomposedof:
(1)GAGs,mostlychondroitinsulfatesandhyaluronicacid,withsmalleramountsofkeratansulfateandheparansulfate;
(2)Proteoglycans,coreproteinswithGAGsidechains;
(3)Proteoglycanaggregates,proteoglycanscovalentlylinkedtolongchainsofhyaluronicacidbylinkprotein;
(4)Glycoproteins,whichattachvariousmatrixcomponentstooneanotherandcellstothematrix,includinglinkprotein,fibronectin,chondronectin;and
(5)TiSsuefluid:
anultrafiltrateofbloodplasma.
2.OrganizationTheconsistencyofhyalinecartilageresultsfromextensivecross-linkingamongitscomponents.Linkprotein(seeabove)attachesthecoreproteinsofproteoglycanstolongchainsofhyaluronicacidtoformproteoglycanaggregates.TheGAGsidechainsoftheproteoglycansassociatewithtypeIIcollagenfibrils.Thechondrocytesareembeddedinthematrixeithersinglyorinisogenousgroupsof2-8cellsderivedfromoneparentcell.Thepotentialspaceoccupiedbyeachchondrocyte,calledalacuna,isvisibleonlyafterthecell'sdeathorafterohrinkageduringtissueprocessing.Thechondrocytesatthecoreofatissuemassareusuallyspheric;thoseattheperipheryareflattenedorelliptic.Thematriximmediatelysurroundingthechondrocytes,calledthecapsular(territorial)matrix,ismoreintenselybasophilicandPAS-positivethantheintercapsular0nterterritorial)matrixbecauseorthehigherconcentrationofsulfated,GAGsandlowerconcentrationofcollageninthecapsularregion.Exceptforarticular(joint)cartilage,allhyalinecartilageissurroundedandnourishedbyperichondrium.Articularcartfiageisnourishedbythesynovialfluidinthejointcavity.
3.HistogenesisAllcartilageisderivedfromembryonicmesenchyme.Duringthedevelopmentofhyalinecartilage,mesenchymalcellsretracttheircytoplasmicextensionsandassumearoundedshape,becomingchondroblasts;atthesametimetheybecomemoretightlypacked,formingamesenchymalcondensation,orprecartilagecondensation.Theincreasedcell-to-cellcontactstimulatescartilagedifferentiation,whichprogressesfromthecenteroutward.Chondroblastsatthecoreofthecondensationarethefirsttosecretecartilaginousmatrixmaterials,whichseparatethecellsfromoneanotheragain.Whenitiscompletelysurroundedbycartilagematrix,achondroblastistermedachondrocyte.Peripheralmesenchymecondensesaroundthedevelopingcartilagemasstoformthefibroblast-containing,denseregularconnectivetissueoftheperichondrium.
4.GrowthCartilagecontinuestogrowby2distinctprocesses.Inbothtypesofgrowth,thenewlyformedchondrocytesdepositmatrixaroundthemselves.Matrixsynthesisisenhancedbygrowthhormone,thyroxine,andtestosteroneandisinhibitedbyestradiolandexcesscortisone.
a.Interstitialgrowthresultsfromthedivisionofexistingchondrocytesandgivesrisetotheisogenousgroups.Itisimportantintheformationofthefetalskeletonandcontinuesintheepiphysealplatesandarticularcartilages(seebelow).
b.Appositionalgrowthresultsfromthedifferentiationintochondrocytesbychondroblastsandstemcellsontheinnersurfaceoftheperichondrium.Itisresponsibleforcontinuedincreaseinthegirthofthecartilagemasses.
5.RepairRepairofcartilagefracturesinvolvesinvasionofthebreachbymesenchymalstemcellsfromtheperichondrium,whichthendifferentiateintochondrocytes.Ifthegapislarge,adenseconnectivetissuescarmayform.
6.FunctionandlocationItsabilitytogrowrapidlywhilemaintainingitsrigiditymakeshyalinecartilageanidealfetalskeletaltissue.Asfetalcartilageisreplacedbybone,hyalinecartilageremainsintheepiphysealplatesattheendsoflongbones,allowingthesebonestogrowinlengthbetweenbirthandadulthood.Atallages,hyalinecartilagewithoutaperichondrium(articularcartilage)coversthearticularsurfacesofbone,whereitsresistancetocompressionanditssmoothtexturemakeitagoodcushionandlow-frictionsurface.Hyalinecartilageisthemostabundantandwidelydistributedcartilagetypeinthebody.Thecostal(rib)cartilages,mostofthelaryngealcartilages,thecartilaginousringssupportingtrachea,andtheirregularcartilageplatesinthewallsofthebronchiarehyalinecartilage.
B.ElasticCartllage:
Elasticcartilageisyellowishwhenfresh.Itismoreflexiblethanhyalinecartilage.
1.CompositionandorganizationElasticcartilageisstructurallyidenticaltohyalinecartilageexceptthatitcontains,inadditiontotypeIlcollagenfibers,adensenetworkofbranchingandanastomosingelasticfibers.Thisnetworkisdensestatthecoreofthecartilagemassandwhenstainedwithelasticstains(eg,Verhoeff'sorWeigert's)mayobscuretheorganizationofthetissue.Thechondrocytescharacteristicallyoccurinisogenousgroups.Aperichondriumsurroundstheelasticcartilagemass.
2.HistogenesisandgrowthElasticcartilagedevelopsfromaprimitiveconnectivetissuecontainingwavybundlesoffibrilsthatdifferinproteincompositionfrombothelastinandcollagen.Fibroblastseventuallysecreteelastin,andthefiberbundlesaretransformedintobranchingelasticfibersbyanunknownmechanism.Thedevelopmentofchondrocytesandproductionoftheothermatrixmaterialsisthesameasinhyalinecartilage.Furthergrowthresemblesthatofhyalinecartilage.
3.FunctionandlocationElasticcartilageprovidesflexiblesupport.Itoccursaloneandwithhyalinecartilage;the2maygradeintoeachotherinasinglecartilagemass.Inhumans,elasticcartilageisfoundintheauricleoftheexternalear,thewallsoftheexternalauditorycanalsandauditorytubes,theepiglottis,andthecorniculateandcuneiformcartilagesofthelarynx.
C.Fibrocartilage:
Fibrocartilageisintermediateincharacterbetweenhyalinecartilageanddenseconnectivetissue.
1.CompositionandorganizationFibrocartilageischaracterizedbyanabundanceoftypeIcollagenfibers;whenseenthroughamicroscopeatlowpower,itcloselyresemblesdenseconnectivetissue.Thegroundsubstancecontainsequalamountsofdermatansulfateandchondroitinsulfate.ThematriximmediatelysurroundingthechondrocytesresemblesthatofhyalinecartilageandcontainssometypeIIcollagen.Thechondrocytesaredistributedincolumnarisogenousgroupsbetween
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Chapter41Cartilage and BoneJunmei Wang