proportion Five zones in cartilage Resting quiescent zone Proliferation growth

Proportion five zones in cartilage resting quiescent

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proportion Five zones in 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 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 Cartilage matrix calcifies, chondrocytes die and deteriorate Ossification zone Chondrocyte deterioration leaves spikes of calcified cartilage at epiphysis-diaphysis junction Spikes eroded by osteoclasts Covered with new bone by osteoblasts Then replaced with spongy bone
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Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate. Resting zone 1 Proliferation zone Cartilage cells undergo mitosis. 2 Hypertrophic zone Older cartilage cells enlarge. 3 Calcification zone Matrix calcifies; cartilage cells die; matrix begins deteriorating; blood vessels invade cavity. 4 Ossification zone New bone forms. Calcified cartilage spicule Osteoblast depositing bone matrix Osseous tissue (bone) covering cartilage spicules
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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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Appositional Growth: Growth in Width Allows lengthening bone to widen Occurs throughout life Osteoblasts beneath periosteum secrete bone matrix on external bone Osteoclasts remove bone on endosteal surface Usually more building up than breaking down Thicker, stronger bone but not too heavy
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Figure 6.11 Long bone growth and remodeling during youth. Bone growth Bone remodeling Cartilage grows here. Bone replaces cartilage here. Cartilage grows here. Bone replaces cartilage here. Articular cartilage Epiphyseal plate Bone that was here has been resorbed. Appositional growth adds bone here. Bone that was here has been resorbed.
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Hormonal Regulation of Bone Growth Growth hormone (GH) Most important in stimulating epiphyseal plate activity in infancy and childhood Thyroid hormone (TH) Controls activity of growth hormone Ensures proper proportions Testosterone (males) and estrogens (females) at puberty Promote adolescent growth spurts End growth by inducing epiphyseal plate closure Excesses or deficits of any of these cause abnormal skeletal growth
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Bone Homeostasis: Bone Remodeling Consists of both bone deposit and bone resorption Occurs at surfaces of both periosteum and endosteum Remodeling units Adjacent osteoblasts and osteoclasts
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Bone Deposit
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