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Embryonic mesenchyme condensing into a sheet of soft

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Unformatted text preview: eddish jelly’ that has replaced yellow reddish Gelatinous marrow of elderly marrow Bone development- 2 methods of ossification (or osteogenesis) …intramembranous & endochondral endochondral Intramembranous ossification Intramembranous Intramembranous= produces flat bones of skull & clavicle Steps of the process~ • Begins w/ embryonic mesenchyme condensing into a sheet of soft tissue (& lots of bld capillaries) • Some of sheet transforms into network of soft trabeculae, other cells differentiate into osteogenic cells • Next, osteogenic cells become osteoblasts, gathering on trabeculae & begin depositing matrix (= osteoid tissue) • Soft collagenous tissue lacking minerals • Larger trabeculae begin depositing Ca3(PO4)2, thus, osteoblasts change into osteocytes once trapped in lucanae • Concurrently, osteoclasts remodel the center for marrow spaces, while osteoblasts remodel the surface to form compact bone • Mesenchyme at the surface gives rise to periosteum Endochonral ossification Endochonral Endochondral ossification Endochondral Endochondral= produces most other bones; vertebrae, pelvic produces & limb bones limb • Mesenchyme transforms into a hyaline cartilage ‘model’ that Mesenchyme is broken down & reorganized & calcified into bone Primary ossification center= 1st step, chondrocytes w/in center Primary of model multiple & swell (forming the p.o.c.) of • Lucanae enlarge, reducing matrix & so model becomes weak • Some perichondrium cells become osteoblasts that produce Some a bony collar around model bony • Diffusion of nuts is cut off & cartilage cells die; perichondrium is Diffusion replaced w/ periosteum replaced • Buds of c.t. from periosteum grow into cartilage & penetrate Buds & breakdown lucanae…transforming p.o.c. into a cavity (p.m.s.) (p.m.s.) Endochonral ossification (cont.) Endochonral Primary marrow space= iinner cavity; osteogenic cells invade nner model & transform into osteoblasts that line the marrow space space Osteoblasts deposit osteoid tissue & then calcify it,...
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