CHP7 Bone Tissue

4 process achondroplastic dwarfism achondroplastic

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Unformatted text preview: owth & remodeling (cont.) Bone Bone grows by 2 methods~ interstitial & appositional growth Interstitial= @ epiphyseal plate, matrix is added to extend epiphyseal length of bone length Appositional= matrix added to external surface to increase matrix width width • Osteoblasts deposit matrix in layers parallel to outer surface Osteoblasts & osteoclasts dissolve bone on inner surface to enlarge marrow cavity marrow • Osteitis deformans & other bone deformities result if one process outpaces the other (Table 7.4) process Achondroplastic dwarfism Achondroplastic Achondroplastic dwarfism= short stature but normal-sized short head and trunk head • Long bones of the limbs stop growing in childhood due to Long failure of chondrocytes (zones 2-3) to multiply & enlarge failure • Condition occurs if spontaneous mutation of allele during Condition DNA replication DNA • Mutant allele is dominant so kids of heterozygous a.d. are Mutant 50:50 50:50 Pituitary dwarfism= deficiency of growth hormone…stunts deficiency growth of all bones (short stature w/ normal proportions) all Bone Physiology Bone Physiology of osseous tissue~ bone is a metabolically active organ that influences entire body by regulating minerals minerals • Mineral deposition; mineral resorption; & homeostasis of Mineral Ca2+ & PO43Ca • 2 iimportant ions required for many compounds (ATP, DNA) & mportant body functions (pH balance, communication, contraction, clotting) Mineralization= crystallization process Mineralization crystallization • Ca2+, PO43- & other ions are removed from blood plasma & deposited in bone tissue deposited Mineral deposition Mineral Steps of the mineralization process~ • Osteoblasts produce collagen fibers that spiral along the Osteoblasts length of osteon in alternating directions length • Fibers become ‘encrusted’ w/ minerals & harden matrix • Crystals forms only when [ion] reaches a critical value (= Crystals solubility product) solubility • Most tissues have inhibitors to prevent calcification, but Most osteoblasts are able to block them to produce salts of matrix osteoblasts • ‘Seed crystals’ serve as positive feedback signals to form Seed positive more crystals since they attract more ions from solution to crystalize crystalize Ectopic ossification= abnormal calcification Ectopic • May occur in lungs, brain, eyes, muscles, tendons (= May calculus in soft...
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