Osteoid is secreted and calcifies Osteoblasts continue to secrete osteoid which

Osteoid is secreted and calcifies osteoblasts

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Osteoid is secreted and calcifies. • Osteoblasts continue to secrete osteoid, which calcifies in a few days. • Trapped osteoblasts become osteocytes. • Mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center.
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Intramembranous Ossification (4 of 4) Figure 6.11 Intramembranous ossification. Mesenchymal cell Osteoblast Osteoid Osteocyte Newly calcified bone matrix Osteoid Osteoblast Mesenchyme condensing to form the periosteum Fibrous periosteum Plate of compact bone Diploë (spongy bone) cavities contain red marrow Blood vessel • Trabeculae just deep to the periosteum are remodeled and replaced with compact bone. • The immature spongy bone in the center is remodeled into mature spongy bone that is eventually filled with red marrow. Ossification center Collagen fiber Osteoblast Compact bone replaces immature spongy bone, just deep to the periosteum. Red marrow develops. 1 2 3 4 Ossification centers develop in the fibrous connective tissue membrane. Osteoid is secreted and calcifies. • Osteoblasts continue to secrete osteoid, which calcifies in a few days. • Trapped osteoblasts become osteocytes. Immature spongy bone and periosteum form. Accumulating osteoid is laid down between embryonic blood vessels, forming a honeycomb of immature spongy bone. • Vascularized mesenchyme condenses on the external face of the bone and becomes the periosteum. • Mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center. Trabeculae of immature spongy bone
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Postnatal Bone Growth Interstitial (longitudinal) growth Increase in length of long bones Appositional growth Increase in bone thickness
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Interstitial Growth: Growth in Length of Long Bones Requires presence of epiphyseal cartilage Epiphyseal plate maintains constant thickness Rate of cartilage growth on one side balanced by bone replacement on other Concurrent remodeling of epiphyseal ends to maintain proportion Result of five zones within cartilage Resting (quiescent) zone Proliferation (growth) zone Hypertrophic zone Calcification zone Ossification (osteogenic) zone
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Interstitial Growth: Growth in Length of Long Bones Resting (quiescent) zone Cartilage on epiphyseal side of epiphyseal plate Relatively inactive Proliferation (growth) zone Cartilage on diaphysis side of epiphyseal plate Rapidly divide pushing epiphysis away from diaphysis lengthening Hypertrophic zone Older chondrocytes closer to diaphysis and their lacunae enlarge and erode interconnecting spaces
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Interstitial Growth: Growth in Length of Long Bones Calcification zone Surrounding cartilage matrix calcifies, chondrocytes die and deteriorate Ossification zone Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction Spicules eroded by osteoclasts Covered with new bone by osteoblasts Ultimately replaced with spongy bone
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Interstitial Growth: Growth in Length of Long Bones Near end of adolescence chondroblasts divide less often Epiphyseal plate thins then is replaced by bone Epiphyseal plate closure Bone lengthening ceases Requires presence of cartilage Bone of epiphysis and diaphysis fuses Females – about 18 years Males – about 21 years
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  • Spring '10
  • Dookwah
  • flat bone, Bone fracture, long bones

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