Complicated shapes Primarily spongy bone and thin covering layer of compact

Complicated shapes primarily spongy bone and thin

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•Complicated shapes: Primarily spongy bone and thin covering layer of compact bone. 3.2 describe the microscopic structure of long bones 1) Diaphysis: Tubular shift of a long bone: Long axis of the bone. Collar of compact bone surrounding marrow cavity (medullary cavity). In adults, medullary cavity contains fat (yellow marrow). 2) Epiphyses: Rounded extremities of a long bone for articulation with other bones. Compact bone forms thin outer layer, interior filled with spongy bone. Thin layer of hyaline (articular) cartilage.
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•Why? -To cover the joint surface, cushioning the opposing bone ends during movement. 3) Epiphyseal line: Between diaphysis and each epiphysis: remnant of epiphyseal plate. 4) Membranes: Cover outer (periosteum) and inner (endosteum) surfaces of long bones. Both contain osteoblasts and osteoclasts. Structure of other bone type •All 3 other types have similar structure. •Compact bone outside, spongy bone inside. •Compact covered with periosteum and spongy lined with endosteum. •Not cylindrical so no shaft or expended ends, contain bone marrow between trabeculae but no well defined bone marrow cavity. Microscopic structure of compact bone Osteon (Haversian) system: •This is the structural unit of compact bone. •Osteon: An elongated cylinder oriented parallel to the long axis of bone. •Think of an osteon as a tiny, weight-bearing pillar. •A single osteon is a group of hallow tubes of bone matrix; think of the rings of a tree; each of the matrix tubes called lamellar bone. •Central (Harversian) canal: contains smalls blood vessels and nerve fibers that serve the osteon’s cell. •Perforating (Volkmann’s) canal: Perpendicular to long axis of bone (and to Haversian canals). •Osteocytes: Mature bone cells, sit within small cavities (lacunae) within bony matrix in areas where adjacent lamellae meet. •Canaliculi: Small canals that connect the lacunae with each other, also connected to central canal of Haversian system. •Interstitial lamellae: Fill the gaps between forming osteons or are leftovers of osteons that were partially destroyed by bone remodeling. •Circumferential lamellae: Sheets of bone located just deep to periosteum, extend around entire circumference of shaft.
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Microscopic structure of spongy bone •Contains trabeculae, lamellarly arranged osteocytes and canaliculi. •Trabeculae arranged along lines of stress, helps bone to resist stress. •Trabeculae only a few cell layers thick, contain irregularly arranged lamellae and osteocytes interconnected by canaliculi. •There are no osteons. •Nutrients diffuse through canaliculi from the marrow spaces between the trabeculae to reach the osteocytes. 3.3 describe bone formation and remodeling and explain the factors that affect them •Osteogenesis or ossification. •Includes formation of bony skeleton in embryos, growth of bones during childhood and adolescence and remodelling and repair of bones in adults.
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•In short bones, only the primary ossification centre is formed, most irregular bones are formed using several distinct ossification centres.
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