2.1 Bone Biology
Bone is a dynamic and changeable tissue that is remodeled constantly throughout life (kang 2012). It is considered to be the arrangement of compact and cancellous bone provides strength and density suitable for the support and protection of the body organs (Feng and Mcdonald 2011; Watts 1999). The skeletal system consists of bone and cartilage (Tamminen 2013). Functions of skeleton are to keep the body upright, help the person to have a good posture, facilitate respiratory movements and protect vital internal organs and the nervous system (Bjugstad 2012). Bone also regulates hematopoiesis by providing places for hematopoietic cell proliferation and differentiation (Sherwood 2007). All humans are born with over 300 bones (Gardner
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Bones may be classified into four types, according to these shape. These are long bones, short bones, flat bones and irregular bones; they are different in anatomy and the mechanism of development (Gardner and Shoback 2007).
2.2 Bone Tissue
Bone tissue is a complex structure that consists of cortical or compact bone and cancellous or spongy or trabecular boneg(Figure 2.1) (Seeman and Delmas 2006). The outside of cortical bone is called periosteum and the inner side is called endosteum (Buckwalter et al. 1996). At the microscopic level, both trabecular and cortical bone are composed of the same structural units referred to as osteons, which are composed of stacks of lamellae ( Rissanen 2013). Osteons of cortical bone are commonly known as Haversian systems, while in trabecular bone, osteons are referred to as packets ( Rissanen 2013). Cortical bone is arranged into osteons,
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Type I collagen accounts for approximately90% of the entire collagen content (Hadjidakis and Androulakis 2006). Type I collagen is produced by osteoblasts and it forms covalent cross-links, which be different from those that are found in other connective tissues (Rissanen 2013). Type I collagen gives bone tensile strength, and also contains peptide motifs which are integrin binding sites for osteoblasts (Mccann et al. 1997), and a structural template for mineral deposition (Landis et al. 1996 ; Landis