OSTEOLOGY:BONEDEVELOPMENT

HumanAnatomyUnit1

InAnatomyToday

GeneralAnatomyofLongandFlatBones• Composition– Compact(Dense)outside– Spongyinside

• Flatbones=diploe• Regionsoflongbone– Diaphysis– Epiphysis– Marrow(medullary)cavity– Epiphysealplatevs.epiphysealline(18-25years)– Periosteum

• Fibrouslayer• Osteogeniclayer(cellularlayer)• Sharpey’sfibers

– Nutrientforamina– Endosteum– Articularcartilage

GrossAnatomyofaLongBone

DevelopmentofBones• Ossification=osteogenesis– depositionofbonetissue– beginsatapprox 4weeksgestation– apparentatapprox 10weeks– bonetissuearisesasconnectivetissuefromembryonicmesenchyme

– Twotypes• Endochondral• Intramembranous

16weeksofdevelopment

EndochondralBoneFormation

• Builtfromahyalinecartilagemodel– Perichondriumpresent

• Ossificationresultsinspongybonefirstthentheboneisremodeledandanouterlayerofcompactboneforms

• 1o centerofossificationindiaphysis• 2o centersofossificationinepiphysis

EndochondralBoneFormation

EndochondralBoneFormation

IncreasingtheLengthofaDevelopingBone

• Growthinbothdirectionsatthemetaphysesorgrowthplates– Ontheshaftside:• Osteoblastsarecontinuouslyreplacingcartilagewithbone

– OntheEpiphysisside:• Newcartilageisbeingproducedatthesamerateofcartilagereplacementontheshaftside

• Growthinoppositedirectionscausesthebonetolengthen

IncreasingtheDiameterofaDevelopingBone

• Appositionalgrowthontheoutersurface• Osteoprogenitorcellsoftheinnerlayeroftheendosteumdifferentiateintoosteoblasts

• Matrixisdepositedtotheouter(periosteal)surface– Addslayersofcircumferentiallamellae

• Marrowcavityenlargesasbonediameterenlarges

IntramembranousBoneFormationDermalBoneFormation

• Ossificationoccursinthedeeperlayersofthedermis• Forms– Roofingbonesoftheskull,mandible,clavicle

• Bonetissuedepositedwithinembryonicorfibrousconnectivetissue

• Mesenchymal cellsdifferentiateintoosteoblasts• Spongybonemayberemodeledtoformmedullarycavitiesorcompactbone– Diploe:spongybonebetween2layersofcompactbone

• Processofbonerepairduetofractures

BoneRepair

IntramembranousBoneFormation