Skeletal SystemBone developmentBone growthOssificationCalcificationSlide 6Intramembranous OssificationIntramembranous ossificationDermal BonesSesamoid BonesSlide 11Slide 12Endochondrial OssificationSlide 14Fetal Skeleton DevelopmentChronic Mechanical StressBone SpurHeterotopic Bone Connective Tissue InjuryInjury SitesSlide 20Slide 21Slide 22Developing Cranial BonesMesenchymal TissueMesenchymal Tissue Becomes VascularizedMesenchymal Cells Aggregate and Differentiate into Osteoprogenitor CellsMesenchymal Cells Aggregate Differentiate into Osteoprogenitor CellsOsteoprogenitor Cells Differentiate into OsteoblastClustered Osteoblasts are Ossification CenterOssification CenterClustered Osteoblast Secrete MatrixOsteoblast Secrete MatrixTrapped Osteoblasts Mature to OsteocytesSpicules Form out from Ossification CenterMesenchymal Cells Continually Differentiate Forming Multiple Ossification SitesSlide 36Spicules of Deposited Bone Form Multiple Ossification CentersSlide 38Spicules from Multiple Ossification Centers Join to Form Spongy BoneSpicules Form Trabeculae of Spongy BoneSpicules Form TrabeculaeOssification Continues in Areas of VascularizationOssification Continues in Areas of VascularizationSlide 44Osteoclast Remodel Spongy Bone to CompactBone RemodelingForms Haversian SystemSkeletal SystemBone development•Bone growth–6 weeks after fertilization- ~25yrs•Regulated by hormones & nutrition–Growth hormone–Sex hormones–Thyroxine•Stimulates Bone growth–Parathyroid•Stimulates osteoclast & osteoblast activity –Calcitonin•Inhibits osteoclast •2 main categories–Osteogenesis–Maintenance & replacement in adultsBone growth•Ossification–Formation of bone–Replacement of existing tissue with bone•Fibrous CT or cartilage, mesenchymal tissue•Calcification–Deposit of calcium salts w/in tissue–Any tissueOssificationCalcificationOssification•Intramembranous ossification–Aka dermal ossification–Derived from mesenchyme or fibrous connective tissue–Embryonic bone development, chronic mechanical stress, CT injury•Endochondrial ossification–Bone replaces existing cartilage framework–jointsIntramembranous Ossification•Mesenchymal cells (aka stem cells) develop into osteoblast–Embryonic–Fibrous connective tissue•Bone & cartilage develop in existing embryonic connective tissue•Remnant mesenchymal cells persist in adult tissueIntramembranous ossification•Dermal bones aka membrane bones–Roofing bones of skull (frontal, parietal)–Mandible–Clavicle–Patella–Sesmoid bones•Typically develop deep in dermis •Membrane bones may develop in other CT under chronic mechanical stress–Ex heterotropic bonesDermal BonesSesamoid BonesSesamoid BonesIntramembranous OssificationEndochondrial OssificationIntramembranous Ossification•Regulation–Fetus- hormonal cues–Mechanical stress–CT injury–Bone Injury–MaintenanceFetal Skeleton DevelopmentChronic Mechanical StressDermal bones develop in CT= bone spursBone SpurHeterotopic BoneConnective Tissue InjuryInjury SitesIntramembranous Ossification•Vascularization of tissue•Mesenchymal cells proliferate, aggregate & differentiate into osteoprogeniter cells•Clustered osteoblast secrete matrix (collagen fibers & ground substance)–Ossification center –Trapped osteoblasts differentiate into osteocytes•Spicules form out from ossification center, calcium salts from blood supply calcify osteoid–Spicules form Trabeculae•Mesenchymal cells continually differentiate forming multiple ossification sites•Ossification proliferates in areas of vascularization•Remodeling of spongy bone to compact boneDeveloping Cranial BonesMesenchymal TissueMesenchymal Tissue Becomes VascularizedMesenchymal Cells Aggregate and Differentiate into Osteoprogenitor CellsMesenchymal Cells Aggregate Differentiate into Osteoprogenitor CellsOsteoprogenitor Cells Differentiate into OsteoblastClustered Osteoblasts are Ossification CenterOssification CenterClustered Osteoblast Secrete MatrixOsteoblast Secrete MatrixTrapped Osteoblasts Mature to OsteocytesSpicules Form out from Ossification CenterMesenchymal Cells Continually Differentiate Forming Multiple Ossification SitesMesenchymal Cells Continually Differentiate Forming Multiple Ossification SitesSpicules of Deposited Bone Form Multiple Ossification CentersMultiple Ossification Sites Form Bone within Mesenchymal TissueSpicules from Multiple Ossification Centers Join to Form Spongy BoneSpicules Form Trabeculae of Spongy BoneSpicules Form TrabeculaeOssification Continues in Areas of VascularizationOssification Continues in Areas of VascularizationSpongy Bone Converted to Compact BoneOsteoclast Remodel Spongy Bone to CompactBone RemodelingForms Haversian