The unique structure and composition of bone allows it to maximize compression

The unique structure and composition of bone allows

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•The unique structure and composition of bone allows it to maximize compression, torsion and bending strength but be of minimal weight. Mechanisms of bone formation •Ossification (osteogenesis) is the process of bone tissue formation. -Formation of bony skeleton begins in month 2 of development. -Postnatal bone growth occurs until early adulthood. -Bone remodeling and repair are lifelong. •Up to about week 8, fibrous membranes and hyaline cartilage of fetal skeleton are replaced with bone tissue. •Endochondral ossification; 17
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-Bone forms by replacing hyaline cartilage. -Bones are called cartilage (endochondral) bones. -Form most of skeleton. •Intramembranous ossification; -Bone develops from fibrous membrane. -Bones are called membrane bones. Mechanisms of bone formation: Endochondral ossification •All bones below the skull (except the clavicles). •It is more complex than intramembranous ossification because the hyaline cartilage must be broken down as ossification proceeds. 1.A bone collar forms around the diaphysis of the hyaline cartilage model. -The mesenchymal cells in the perichondrium specialize into osteoblasts. -Osteoblast secrete osteoid against the hyaline cartilage diaphysis. 2.Cartilage calcifies in the center of the diaphysis and then develops cavities. -Chondrocytes die and the matrix start to deteriorate. -Opens up cavities. 3.The periosteal bud invades the internal cavities and spongy bone forms. 4.The diaphysis elongates and a medullary cavity forms. -Osteoclasts break down the newly formed spongy bone and open up a medullary cavity in the center of the diaphysis. 5.The epiphyses ossify. -Secondary ossification reproduces almost the same events as primary ossification except the spongy bone is retained and no medullary cavity is forms. -Hyaline cartilage remains; *On the epiphyseal surfaces as the articular cartilages. *At the junctions of diaphysis and epiphyses where it forms the epiphyseal plates. •In short bones, only the primary ossification centre is formed; most irregular bones are formed using several distinct ossification centres. •Long bones will have two ossification centers. 18
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Mechanisms of bone formation: Intramembranous ossification •Begins within fibrous connective tissue membranes formed by mesenchymal cells. •Forms frontal, parietal, occipital, temporal, and clavicle bones. Postnatal bone growth: Long bone Interstitial (longitudinal) growth; •During infancy and youth, long bones lengthen entirely by interstitial growth of the epiphyseal plates and all bones grow in thickness by appositional growth. •Most bones stop growing during adolescence of in early adulthood. -Some facial bones (nose and lower jaw) continue to grow throughout life. •Interstitial growth requires presence of epiphyseal cartilage in the epiphyseal plate. •Epiphyseal plate maintains constant thickness. -Rate of cartilage growth on one side balanced by bone replacement on other.
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