Bone marrow is found in the medullary cavities – the centres of bones. The bone marrow is where circulating blood cells are produced – a process known as ...SkiptomaincontentHome//Publicinformation//BiteSizedImmunology//OrgansandTissues//BoneMarrowEnglishEspañolBoneMarrowDownloadbonemarrow.pdf(799.71KB)DownloadBonemarrow.ppt(1.43MB)AndyMcLarnon,UniversityofBirmingham,UKBonemarrowisfoundinthemedullarycavities–thecentresofbones.Thebonemarrowiswherecirculatingbloodcellsareproduced–aprocessknownashaematopoiesis.Earlyoninahuman’slife,thistakesplaceinmanybones,butduringdevelopmenthaematopoiesisincreasinglycentresonflatbonessothatbypuberty,bloodproductiontakesplacepredominantlyinthesternum,vertebrae,iliacbonesandribs.Bonemarrowundergoinghaematopoiesisiscolouredredduetothepresenceofredbloodcells,whereasbonemarrowthatisnotundergoinghaematopoiesisisyellow.Theredmarrowconsistsoflongtrabeculae(beam-likestructures)withinasponge-likereticularframework.Spacesaroundthisframeworkarefilledwithfatcells,stromalfibroblastsandbloodcellprecursors.AhealthybonemarrowbiopsyisshowninFigure1.Figure1.Haematoxylin-Eosinstainofhealthybonemarrow(fromhttp://bonemarrowbiopsy.wordpress.com/normal-results/)Thehaematoxylinhasstainedthecells’nucleipurpleandtheeosinhasstainedthecells’cytoplasmpink.Thewhitepatchesarefatstoredinfatcells.Duringthedevelopmentofthebloodcells,thesehaematopoieticprecursorsmigratefromthesubendostealregion(theinnerbonesurface)towardsacentralregion(Figure2).Thematuredbloodcellsexitthroughadensenetworkofvascularsinuses.Figure2.BoneMarrowMorphology.AdaptedfromNagasawaNatRevImmunol.2006Feb;6(2):107-16.Duringhaematopoiesisthehaematopoieticstemcells(HSC)divide,andonedaughtercellremainsinthebonemarrowtocontinuerenewingtheHSCpool.Theotherdaughtercellwillpassthroughseveralstagesofdevelopment(seeFigure4)tobecomeamaturebloodcellandleavethebonemarrowtoenterthecirculation.Figure4.AmodelforbloodandtissueproductioninBoneMarrow.HSCs(haematopoeiticstemcells)areself-renewingstemcellsthatcandiffere