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Ajman University of Science & Technologyjman University of Science & Technologyl f if iaculty of Dentistryaculty of Dentistry

Histology & Cell Biologyistology & Cell Biologyy gyy gy08 01 1128 01 112

l ll h hl h hr. Alr. Al-Moutassem Billah Khairoutassem Billah Khair

Boneone

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Boneoneoneone osseousosseous ssue

ssue ss spec a zespec a ze ormorm oo suppor ngsuppo

r ng ssue

ssue nn w cw c

thethe extracellularextracellular matrixmatrix isis mineralizedmineralized.. ThisThis producesproduces anan extremelyextremely hardhard tissuetissue

ca ableca able oo rovidinrovidin su ortsu ort or or leshlesh structures,structures, rotectionrotection oror vitalvital or ansor ans

andand storagestorage ofof bonebone marrowmarrow.. BoneBone servesserves asas aa storagestorage ofof calciumcalcium andand phosphate,phosphate, andand otherother mineralsminerals..

BoneBone isis vascularvascular tissuetissue andand metabolitesmetabolites exchangeexchange betweenbetween bonebone cellscells andand bloodblood

capillariescapillaries dependsdepends onon communicationcommunication throughthrough thethe canaliculi,canaliculi, becausebecause theythey areareuna euna e o o use use rougroug e e ca c e ca c e ma r xma r x ..

BoneBone consistsconsists of of bonebone tissue,tissue, hemopoietichemopoietic tissue,tissue, fatfat tissue,tissue, bloodblood vessels,vessels,

.. BoneBone tissuetissue isis classifiedclassified intointo compactcompact (dense)(dense) andand spongyspongy (cancellous)(cancellous) bonebone..

DenseDense la erla er ormsorms thethe outsideoutside oo thethe bonebone andand cancellouscancellous ormsorms aa meshwormeshwor inin

thethe interiorinterior ofof thethe bonebone.. TheThe spacesspaces ofof thethe meshworkmeshwork areare occupiedoccupied byby marrowmarrow andand

bloodblood vesselsvessels..

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Boneone,, ,,

mineralizedmineralized extracellularextracellular matrixmatrix ((7070%% inorganicinorganic && 3030%% organicorganic byby weight)weight)..

TheThe mineralmineral 5050%% oo thethe drdr wei htwei ht oo thethe bonebone matrixmatrix isis mainl mainl calciumcalcium

phosphatephosphate inin thethe formform ofof hydroxyapatitehydroxyapatite crystalscrystals [[ CaCa1010 (PO(PO44))66 (OH)(OH)22 ]].. ItIt alsoalsocontainscontains small small proportion proportion of of MgCOMgCO22 ,, CaCOCaCO22 ,, citrate,citrate, F,F, Na,Na, K,K, and and havehave

a n ty a n ty or or eavyeavy metameta ra oact vera oact ve env ronmentaenv ronmenta po utants po utants..

TheThe collagencollagen fibersfibers areare typetype II andand formform thethe highhigh contentcontent ((9090%%)) ofof organicorganic..

TheThe groundground substancesubstance ((1010%% ofof thethe organicorganic matrix),matrix), likelike inin cartilage,cartilage, containscontains

erataneratan sul ate,sul ate, chondroitinchondroitin sul ate,sul ate, h aluronich aluronic acid,acid, e ce te ce t thatthat thethe ro ortionro ortion

ofof sulfatedsulfated glycoproteinsglycoproteins isis muchmuch lessless thanthan inin cartilagecartilage.. TheThe glycoproteinsglycoproteins maymay bebe

responsibleresponsible forfor promotingpromoting calcificationcalcification ofof bonebone matrixmatrix..

TheThe bonebone cellscells areare derived derived fromfrom mesenchymemesenchyme andand knownknown asas osteoprogenitorosteoprogenitor

cellscells (osteogenic),(osteogenic), osteoblasts,osteoblasts, osteocytesosteocytes andand osteoclastsosteoclasts..

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OsteogenicOsteogenic cellscells areare foundfound inin developingdeveloping bonebone andand onon surfacessurfaces ofof maturemature bonebone..

differentiatedifferentiate toto formform osteoblastsosteoblasts..

OsteoblastsOsteoblasts areare responsibleresponsible for for thethe synthesissynthesis and and secretionsecretion of of thethe organicorganic

componentscomponents ofof thethe matrixmatrix--osteoidosteoid;; osteoidosteoid rapidlyrapidly undergoesundergoes mineralizationmineralization toto

formform bonebone.. OsteoblastsOsteoblasts areare foundfound asas aa continuouscontinuous layerlayer onon thethe surfacessurfaces ofof thetheone,one, espec a yespec a y ur ngur ng eve opmeneve opmen anan grow grow oo ee oneone.. eyey areare cu o acu o a

toto lowlow columnarcolumnar cellscells withwith prominentprominent nucleusnucleus andand cytoplasmiccytoplasmic organellesorganelles.. WhenWhen

thethe stosto thethe s nthesiss nthesis rocessrocess thethe becomebecome lattened lattened--osteo enicosteo enic cellscells.. SomeSome

osteoblastsosteoblasts becomebecome trappedtrapped withinwithin thethe bonebone asas osteocytesosteocytes..

OsteocytesOsteocytes areare derived derived from from osteoblastsosteoblasts whenwhen theythey becomebecome surrounded surrounded byby

newlynewly formedformed matrixmatrix duringduring developmentdevelopment ofof thethe bonebone..

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EachEach osteocyteosteocyte occupiesoccupies ownown

lacunalacuna.. TheyThey havehave almond almond

processesprocesses byby which,which, theythey cancancommunicatecommunicate withwith the the

adjacentadjacent cellscells toto exchangeexchange

thethe moleculesmolecules.. OsteocytesOsteocytes

cytoplasmiccytoplasmic organellesorganelles..

Osteoc tesOsteoc tes areare res onsibleres onsible

forfor maintenancemaintenance ofof thethe bonebone

matrixmatrix andand theirtheir deathdeath leadsleads

toto resorptionresorption ofof bonebone matrixmatrix..

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LacunaeLacunae areare smallsmall cavitiescavities withinwithin thethe bonebone matrixmatrix andand theythey communicatecommunicate

byby tinytiny channelschannels knownknown asas canaliculi,canaliculi, thatthat containcontain cytoplasmiccytoplasmic processesprocesses ofof

osteocytesosteocytes.. TheThe communicationcommunication taketake placeplace inin 33DD directionsdirections..

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OsteoclastsOsteoclasts areare multinucleate,multinucleate, veryvery

,,surfacesurface facingfacing thethe bonebone matrixmatrix.. TheyThey

areare probablyprobably derived derived from from fusionfusion ofof

monocytemonocyte--phagocyte phagocyte systemsystem cellscells..TheyThey areare scatteredscattered onon thethe surfacessurfaces ofof

ee one one w n w n epress ons epress ons nownnown

asas HowshipsHowships lacunaelacunae..

resorptiveresorptive processes processes associated associated withwith

continuouscontinuous remodelingremodeling ofof bonebone.. TheyThey

secretesecrete collagenasecollagenase andand otherother enzymesenzymesandand providingproviding lowlow pH,pH, promotingpromoting thethe

digestiondigestion ofof collagencollagen fibersfibers..

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Boneone surfacesurfaces TheThe externalexternal surfacesurface ofof thethe bonebone isis coveredcovered byby aa sheathsheath ofof densedense connectiveconnective

tissuetissue calledcalled periosteumperiosteum.. ItIt consistsconsists ofof anan outerouter fibrousfibrous layerlayer thatthat resemblesresembles otherother

enseense connectiveconnective tissuestissues anan anan innerinner ce u arce u ar ayerayer t att at containscontains t et e osteogenicosteogenic

cells,cells, whichwhich areare responsibleresponsible forfor thethe appositionalappositional growthgrowth andand repairrepair ofof thethe bonebone..

knownknown asas SharpeysSharpeys fibersfibers.. PeriosteumPeriosteum isis notnot presentpresent onon thethe articulararticular surface,surface,

whichwhich isis coveredcovered byby hyalinehyaline cartilagecartilage--articulararticular cartilagecartilage.. TheThe articulararticular cartilagecartilageisis exposedexposed toto thethe jointjoint cavitycavity andand isis notnot coveredcovered withwith perichondriumperichondrium..

TheThe internalinternal surfacessurfaces ofof thethe bonebone areare lined lined byby endosteumendosteum.. ItIt isis aa layerlayer ofof

connec veconnec ve ssuessue ce sce s con a n ngcon a n ng os eogen cos eogen c ce sce s.. ee ce sce s areare a ene a ene an anhavehave capabilitycapability toto dividedivide andand differentiatedifferentiate intointo osteoblastsosteoblasts..

formform aa supplysupply ofof osteoblastsosteoblasts forfor growthgrowth andand repairrepair ofof bonebone..

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Periosteum

Bone Sharpeys fibers

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TypesTypes ofof bonebone tissuestissues

GeneralGeneral appearanceappearance ofof bonebone inin crosscross sectionsection showsshows densedense areasareas withoutwithout cavitiescavities--

compactcompact bonebone andand areasareas withwith numerousnumerous interconnectinginterconnecting cavitiescavities--cancellouscancellous bonebone..

BotBot compactcompact anan cance ouscance ous onesones aveave t et e samesame asicasic microscopicmicroscopic isto ogicaisto ogica

structurestructure.. MicroscopicMicroscopic examinationexamination of of bonebone showsshows twotwo typestypes:: primary,primary,

-- --

PrimaryPrimary bonebone tissuetissue isis thethe firstfirst bonebone toto appearappear inin embryonicembryonic developmentdevelopment andand

inin fracture fracture repairrepair and and otherother repairrepair processesprocesses.. ItIt isis characterized characterized byby irregularirregulararrayarray ofof finefine collagencollagen fibers,fibers, aa lowerlower contentcontent ofof minerals,minerals, andand aa higherhigher numbernumber ofof

osteocytesosteocytes thanthan secondarysecondary bonebone.. ItIt isis temporarytemporary and and replaced replaced inin adultsadults byby

secon arysecon ary oneone excepexcep ewew areasareas e e:: nearnear su uressu ures oo s us u ones,ones, nn oooo soc e soc eandand inin thethe insertioninsertion ofof somesome tendonstendons..

arrangementarrangement ofof collagencollagen fibersfibers inin specificspecific structuresstructures knownknown asas lamellaelamellae..

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ame ar secon ary one n w c e co agen ers can e para e o eac o er a e or

organized concentrically around neurovascular channels, to constitute the haversian systems.

Among the numerous haversian systems are some interstitial lamellae.

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AdultAdult bonebone

MatureMature compactcompact bonebone isis largelylargely composed composed of of cylindrical cylindrical unitsunits--osteonsosteons oror

HaversianHaversian systemssystems.. ItIt consistsconsists ofof concentricconcentric lamellaelamellae ofof bonebone matrixmatrix surroundingsurrounding

,,

supplysupply of of thethe osteonosteon.. CanaliculiCanaliculi containingcontaining thethe processes processes of of osteocytesosteocytes arearearran ed arran ed mostlmostl inin aa radialradial atternattern withwith res ectres ect toto thethe canalcanal.. EachEach HaversianHaversian

systemsystem isis aa longlong cylindercylinder parallelparallel toto thethe longlong axisaxis ofof thethe diaphysisdiaphysis.. ItIt consistsconsists ofof

centralcentral canalcanal surroundedsurrounded byby 44--2020 concentricconcentric lamellaelamellae..BetweenBetween thethe osteonsosteons areare remnantsremnants ofof thethe previousprevious osteonalosteonal lamellaelamellae interstitialinterstitial

lamellae,lamellae, thatthat nono longerlonger surroundingsurrounding HaversianHaversian canalscanals..

ee ou ermosou ermos aspecaspec oo ee compaccompac oneone ereere areare ewew ame aeame ae ca eca e ou erou ercircumferentialcircumferential lamellae,lamellae, thatthat laidlaid downdown atat thethe bonebone surfacesurface byby osteoblastsosteoblasts ofof

thethe eriosteumeriosteum.. At At thethe innerinner medullarmedullar as ect,as ect, similarsimilar butbut irre ularirre ular innerinner

circumferentialcircumferential lamellaelamellae mergemerge withwith trabeculaetrabeculae ofof cancellouscancellous bonebone..

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AdultAdult bonebone

TheThe collagencollagen fibersfibers inin thethe concentricconcentric lamellaelamellae inin anan osteonosteon areare laidlaid downdown parallelparallel

toto oneone anot eranot er nn anyany g veng ven ame aame a ut ut nn erent erent rect onsrect ons nn a acenta acent

lamellae,lamellae, givinggiving aa greatgreat strengthstrength toto thethe osteonosteon..

whichwhich thethe blood blood vesselsvessels andand nervesnerves travel travel from from thethe periosteal periosteal and and endosteal endosteal

surfacessurfaces toto reachreach thethe osteonalosteonal canals,canals, alsoalso theythey connectconnect osteonalosteonal canalscanals toto oneoneanotheranother.. TheyThey areare notnot surroundedsurrounded byby concentricconcentric lamellaelamellae..

TheThe canalscanals inin compactcompact bonebone areare linedlined byby endosteumendosteum..

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one emo e ng s ow ng gene a ons o ave s an sys ems an e success ve con u ons

to the formation of intermediate, or interstitial, lamellae. Remodeling is a continuous process

responsible for bone adaptations, especially during growth.

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PartPart ofof HaversianHaversian systemsystem showsshows

thethe numerousnumerous canaliculicanaliculi thatthat

perm tperm t commun cat oncommun cat on etweenetween

lacunaelacunae andand withwith thethe HaversianHaversian

provideprovide nourishmentnourishment forfor aa chainchain

ofof aboutabout 1515 cellscells..EachEach HaversianHaversian systemsystem isis

surroundedsurrounded byby aa depositdeposit of of

amorp ousamorp ous ma er ama er a ca e ca ecementcement thatthat consistsconsists of of

mineralizedmineralized matrimatri withwith ewew

collagencollagen fibersfibers..

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uu one one

SpongySpongy bonebone isis veryvery similarsimilar toto compactcompact bonebone exceptexcept thatthat thethe tissuetissue isis arrangedarranged

sizesize areare presentpresent betweenbetween thethe bonebone tissuetissue.. TheThe matrixmatrix ofof thethe bonebone isis lamellatedlamellated.. IfIfthethe trabeculaetrabeculae areare sufficientlysufficiently thickthick theythey willwill containcontain osteonsosteons..

TheThe medullarymedullary cavitycavity andand thethe spacesspaces inin spongyspongy bonebone containcontain bonebone marrowmarrow..

RedRed bonebone marrowmarrow consistsconsists of of developingdeveloping blood blood cellscells inin differentdifferent stagesstages of ofdevelopmentdevelopment and and aa networknetwork of of reticularreticular fibers fibers and and cellscells.. InIn laterlater stagesstages of of

growthgrowth andand inin thethe adult,adult, whenwhen thethe raterate ofof bloodblood cellcell formationformation hashas diminished,diminished,

yellowyellow marrowmarrow..

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A: Thick section of bone illustrating thecortical compact bone and the spongy bone.B: Microscopic section of cancellous bone.f

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BoneBone formationformation

ee eve opmeneve opmen oo aa one one s s ra ona y ra ona y c ass e c ass e as as en oc on raen oc on ra ananintramembranousintramembranous ossificationossification.. TheThe distinctiondistinction betweenbetween twotwo typestypes restsrests onon

whetherwhether aa cartila ecartila e modelmodel servesserves asas thethe recursorrecursor oo thethe bonebone endochondral endochondral oror

whetherwhether thethe bonebone isis formed formed byby aa simplersimpler method method;; directdirect replacementreplacement of ofmesenchymemesenchyme byby bonebone (intramembranous)(intramembranous).. TheThe bonesbones ofof thethe extremitiesextremities andand thosethose

oo parts parts oo t et e axiaaxia s e etons e eton t att at ear ear weig tweig t eve opeve op y y en oc on raen oc on ra

ossificationossification (short(short && longlong bones,bones, vertebrae,vertebrae, pelvispelvis andand bonesbones ofof thethe basebase ofof thethe

mandiblemandible developdevelop byby intramembranousintramembranous ossificationossification..

InIn bothboth processes, processes, thethe bonebone tissuetissue thatthat appearsappears first first isis primary, primary, whichwhich isis

temporarytemporary tissuetissue and and isis soonsoon replaced replaced byby thethe lamellarlamellar--secondarysecondary bonebone.. ThisThisreplacementreplacement taketake placeplace byby bonebone remodeling,remodeling, whichwhich alsoalso occursoccurs throughoutthroughout adultadult

ee..

BoneBone developmentdevelopment isis controlledcontrolled byby growth,growth, thyroidthyroid andand thethe sexsex hormoneshormones..

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Intramembranousntramembranous ossificationssification--..

mesenchymalmesenchymal cellscells differentiatedifferentiate osteogenicosteogenic cellscells (bone(bone blastema)blastema) developdevelop inin

osteoblastsosteoblasts (osteoblasts(osteoblasts ++ collagencollagen fibersfibers immersedimmersed inin densedense groundground substance)substance)

22.. OsteoblastsOsteoblasts secretesecrete newnew bonebone matrixmatrix (osteoid)(osteoid) aroundaround themselves,themselves, whichwhich laterlaterbecomebecome calcifiedcalcified (deposition(deposition ofof hydroxyapatitehydroxyapatite crystals)crystals)..

33.. SomeSome osteoblastsosteoblasts becomebecome surroundedsurrounded byby matrix,matrix, whichwhich becomebecome osteocytesosteocytes

spiculesspicules ofof bonebone areare formedformed (surrounded(surrounded byby aa layerlayer ofof osteoblasts)osteoblasts)..

.. p cu esp cu es oo one one ncreasencrease nn s zes ze y y appos t onaappos t ona growt growt asas ayersayers oo one one

(center(center ofof ossification)ossification) spongyspongy bonebone..

.. ..

66.. PrimaryPrimary bonebone tissuetissue undergoesundergoes remodelingremodeling andand replaced replaced byby secondarysecondary bonebone..

ThenThen twotwo la ersla ers oo com actcom act bonebone lateslates will will arisearise inin thethe outerouter ortionortion oo

intramembranousintramembranous bonebone andand aa spongyspongy bonebone (diplo(diplo)) occupiesoccupies thethe centercenter ofof thethe flatflat

bonebone..

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77.. BoneBone marrow,marrow, endosteumendosteum and and periosteum periosteum developdevelop from from undifferentiated undifferentiated

mesenchymalmesenchymal cellscells thatthat dodo notnot undergoundergo ossificationossification..

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Endochondralndochondral (intracartilaginous)intracartilaginous) ossificationssification11.. InnerInner mesenchymalmesenchymal cellscells of of thethe perichondriumperichondrium aroundaround thethe diaphysisdiaphysis of of thethe

cartilagecartilage modelmodel differentiatedifferentiate osteogenicosteogenic cellscells osteoblastsosteoblasts thinthin layerlayer ofof

-- ..

22.. TheThe bonebone collarcollar preventsprevents diffusiondiffusion ofof nutrientsnutrients toto thethe centercenter ofof cartilagecartilagechan eschan es be inbe in toto occuroccur inin thisthis areaarea (lacunae(lacunae raduall raduall enlar e,enlar e, matrixmatrix calci ied,calci ied,

chondrocyteschondrocytes diedie && smallsmall cavitiescavities formform inin thethe matrix)matrix)..

33.. WhileWhile thethe calcified calcified cartilagecartilage disintegrated,disintegrated, aa collectioncollection of of mesenchymal,mesenchymal,osteogenicosteogenic cellscells && bloodblood vesselsvessels penetratepenetrate thethe bonybony collarcollar fromfrom itsits periosteumperiosteum toto

thethe reachreach interiorinterior ofof cartilagecartilage andand toto formform anan osteogenicosteogenic budbud..

.. esenc ymaesenc yma os eogen cos eogen c ce sce s os eo as s os eo as s surrounsurroun e e remnan sremnan s oocalcifiedcalcified cartilagecartilage andand covercover itit byby bonebone matrixmatrix cartilagecartilage spiculesspicules replacedreplaced byby

bonebone s iculess icules rimarrimar ossi icationossi ication centercenter oo develo indevelo in lonlon bonebone isis ormed ormed..

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55.. PrimaryPrimary ossificationossification centercenter

endsends of of thethe bonebone (epiphysis)(epiphysis)

forms forms spongyspongy bonebone inin thethe centercenter

andand compactcompact inin thethe peripheryperiphery ofof

thethe shaft shaft (collar(collar growth)growth)

er c on r umer c on r um ecomesecomes per os eumper os eum..

66.. SecondarySecondary ossificationossification centercenter

similarsimilar toto thatthat ofof primaryprimary oneone..

77.. SpongySpongy bonebone inin epiphysisepiphysis isis

formedformed withoutwithout definitivedefinitive marrowmarrowcavities,cavities, thinthin shellshell ofof compactcompact bonebone

nn ee sur acesur ace anan ayerayer oo car agecar age

remainsremains onon thethe articulararticular surfacesurface..

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Epiphysealpiphyseal platelateTheThe areaarea betweenbetween thethe shaftshaft andand epiphysisepiphysis isis cartilagecartilage tissuetissue calledcalled epiphysealepiphyseal

cartilage,cartilage, whichwhich isis responsibleresponsible for for thethe growth growth of of bonebone inin length,length, and and itit

..

startingstarting fromfrom thethe epiphysealepiphyseal sideside::RestinRestin zonezone:: h alineh aline cartila ecartila e withoutwithout mor holo icmor holo ic chan eschan es inin thethe cellscells..

ProliferatingProliferating zonezone:: chondrocyteschondrocytes dividedivide rapidlyrapidly andand formform columncolumn ofof stackedstacked

cellscells parallelparallel toto thethe longlong axisaxis ofof thethe bonebone..HypertrophicHypertrophic zonezone:: largelarge chondrocyteschondrocytes whosewhose cytoplasmcytoplasm accumulatedaccumulated glycogenglycogen

andand thethe matrixmatrix betweenbetween cellscells isis veryvery thinthin..

CalcifiedCalcified cartilagecartilage zonezone:: chondrocyteschondrocytes diedie andand thethe thinthin matrixmatrix becomebecome calcifiedcalcifiedbyby thethe depositdeposit ofof hydroxyapatitehydroxyapatite crystalscrystals..

byby osteoblastsosteoblasts fromfrom thethe diaphysisdiaphysis areaarea..

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