UNIT 4.2 BONE TISSUE Foundation copie 9.pdf

OUTLINE 4.2 Bone tissue. 4.2.1. General characteristics of bone tissue. 4.2.2. Functions of bone tissue and skeletal system. 4.2.3. Types of bone. 4.2.4. Structure of the bone: parts of a long bone. 4.2.5. Histology of bone tissue. 4.2.6. Types of bone tissue. 4.2.7. Microscopic structure of bones....

OUTLINE 4.2 Bone tissue. 4.2.1. General characteristics of bone tissue. 4.2.2. Functions of bone tissue and skeletal system. 4.2.3. Types of bone. 4.2.4. Structure of the bone: parts of a long bone. 4.2.5. Histology of bone tissue. 4.2.6. Types of bone tissue. 4.2.7. Microscopic structure of bones. 4.2.8. Irrigation and innervation of bone tissue. 4.2.9. Bone formation. Osteogenesis. 4.2.10. Bone remodelling. © Copyright Universidad Europea. Todos los derechos reservados BONE FORMATION WHEN does it happen?? Osteogenesis or ossification is the process by which bone is formed. Begins when mesenchymal cells provide the template for subsequent ossification. Substitution of preexisting connective tissue by bone tissue. Types: § Intramembranous ossification: formation of bone directly from or within mesenchyme. § Endochondral ossification: formation of bone from hyaline cartilage models. © Copyright Universidad Europea. Todos los derechos reservados Imperfect osteogenesis STAGES in BONE FORMATION 1st Differentiation of osteoprotenitorOsteoblast cells 2nd Formation of osteoid-organic matrix (osteoblasts) 3rd Mineralization of osteoid-organic matrix (calcification - precipitation hydroxyapatite) 4th Appearance of lacunae (osteocytes – calcified matrix) © Copyright Universidad Europea. Todos los derechos reservados INTRAMEMBRANOUS OSSIFICATION Formation and growth of flat bones of skull and mandible Ø An ossification centre forms from mesenchymal cells as they convert to osteoblasts. 8th week of gestation. Ø Osteoblasts secrete osteoid matrix (with collagen fibres). Ø Calcification: osteoid matrix surrounds the cell and minerals start precipitating on collagen fibres. Osteoid matrix hardens (calcifies) as the osteoblast becomes an osteocyte. Internal use ENDOCHONDRAL OSSIFICATION Formation of most bones of the skeleton Involves replacement of hyaline cartilage by bone. 1. Mesenchymal cells form a hyaline cartilage model of the bone during development (mesenchymal cells – chondroblasts – matrix – chondrocytes). Perichondrium covers the cartilage model. 2. Growth of cartilage model: • Interstitial growth: growth in length by chondrocyte cell division and matrix formation. • Appositional growth: growth in width by formation of new matrix on the periphery by new chondroblasts from the perichondrium. 3. Cells in the mid region burst and change pH, triggering calcification and chondrocyte death (spaces left behind: LACUNAE). Internal use GROWTH of BONE GROWTH IN LENGTH 1. Growth of cartilage in the epiphyseal side of the epiphyseal plate. 2. Replacement of cartilage with bone in the diaphyseal side of the epiphyseal plate. © Copyright Universidad Europea. Todos los derechos reservados GROWTH IN LENGTH STRUCTURE OF THE GROWTH PLATE The activity of the epiphyseal plate is the only means by which the diaphysis can increase in length. When the epiphyseal plate closes, it is replaced by bone. When this happens, the bone has completed its growth in length. © Copyright Universidad Europea. Todos los derechos reservados § § § § zone of resting cartilage zone of proliferating cartilage zone of hypertrophic cartilage zone of calcified cartilage GROWTH IN LENGTH STRUCTURE OF THE GROWTH PLATE Zone of resting cartilage § anchors growth plate to bone Zone of proliferating cartilage § rapid cell division (stacked coins) Zone of hypertrophic cartilage § cells enlarged & remain in columns Zone of calcified cartilage § thin zone, cells mostly dead since extracellular matrix is calcified § osteoclasts removing matrix § osteoblasts & capillaries move in to create bone over calcified cartilage. ENDOCHONDRAL OSSIFICATION. © Copyright Universidad Europea. Todos los derechos reservados GROWTH in WIDTH APPOSITIONAL GROWTH © Copyright Universidad Europea. Todos los derechos reservados https://www.youtube.com/watch?v=_xlJWZvVgRM ALTERATIONS in BONE GROWTH Rickets Achondroplasia © Copyright Universidad Europea. Todos los derechos reservados Acromegaly