Basics of Bone Biology
Bone is the major constituent of the skeleton which is a hallmark of all higher vertebrates. Besides the protection of internal organs and the support of body structures, the most important functions of bone are to serve as an attachment site for muscles
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Martina Rauner, Nicola Stein, Lorenz C. Hofbauer
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Introduction to Bone
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Bone Function and Structure
Bone is the major constituent of the skeleton which is a hallmark of all higher vertebrates. Besides the protection of internal organs and the support of body structures, the most important functions of bone are to serve as an attachment site for muscles allowing locomotion and provide a cavity for hematopoiesis in the bone marrow (Mendez-Ferrer et al. 2010; Zaidi 2007). Moreover, bone has a central role in mineral homeostasis as it functions as a reservoir for inorganic ions that can be mobilized rapidly on metabolic demand. Although bone is often considered an inert, static material, it is a highly organized, living tissue that undergoes constant remodeling. Different cell lineages have emerged to serve distinct skeletal functions. While cells from the hematopoietic lineage, such as osteoclasts, break down bone tissue to remove old and damaged bone, or release calcium to maintain calcium homeostasis, cells from the mesenchymal lineage, including chondroblasts, fibroblasts and osteoblasts construct and later remodel bone tissue (Jiang et al. 2002). Osteoblasts produce the organic components of the extracellular matrix, which mainly includes type I collagen (approximately 95 %), but also non-collagenous proteins (i. e. osteocalcin, osteopontin, osteonectin, bone sialoprotein) and proteoglycans. The inorganic matrix predominantly contains calcium and phosphorus, appearing as hydroxyapatite crystals ([3Ca3(PO4)2](OH)2), and is deposited into the collagenous matrix. This complex organization confers rigidity and strength to the skeleton while maintaining a high degree of elasticity. Dipl.-Ing. Dr. Martina Rauner Division of Endocrinology, Diabetes and Metabolic Bone Diseases, Department of Medicine III, Dresden Technical University Medical Center, Fetscherstr. 74, 01309 Dresden, Germany [email protected] Pietschmann et al., Principles of Osteoimmunology, Molecular Mechanisms and Clinical Applications; DOI 10.1007/978–3–7091–0520–7, © SpringerWienNewYork 2012
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1 Basics of Bone Biology
Two types of osseous tissues are found in all bones: cortical or compact bone and trabecular or cancellous bone, sometimes also referred to as spongy bone (Fig. 1). Cortical bone is mainly found in the shafts of long bones (diaphyses) and is made of numerous overlapping cylindrical units termed Haversian systems or osteons. The central Haversian canal, containing the blood vessel and nerves, is surrounded by densely packed collagen fibrils which are formed into concentric lamellae. Osteocytes, terminally differentiated osteoblasts, are located between concentric lamellae and are connected to each other via canaliculi, allowing the exchange of nutrients and metabolic waste and the sensation of mechanical stress. Volkmann’s canals are responsible for the conjunction of blood vessels from the inner and outer bone surfaces to the vessels of the Haversian canals. The dense organization of cortical
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