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Chapter 6 Bones and The Skeletal System

About mechanical stresses cells of osseous tissue

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Unformatted text preview: Osteoclasts develop in bone marrow by the fusion of the same stem cells that give rise to monocytes of the blood Reside in pits called resorption bays that they have eaten into the surface of the bone Matrix of Osseous Tissue Dry weight is 1/3 organic & 2/3 inorganic matter Organic matter Inorganic matter collagen, glycosaminoglycans, proteoglycans & glycoproteins Combination provides for strength & resilience 85% hydroxyapatite (crystallized calcium phosphate salt) 10% calcium carbonate other minerals minerals resist compression; collagen resists tension Role of Collagen & Minerals Osteons or haversian systems Compact Bone: microstructure cylinders of tissue formed from layers of matrix concentrically arranged around a blood vessel osteocytes connected to each other and the haversian blood supply by tiny cell processes branches from nutrient arteries that run perpendicular to the haversian canals lamellae are the individual layers haversian canal holds the blood vessels Perforating canals or Volkmann canals Circumferential or outer lamellae Histology of Compact Bone Microstructure (histology) of bone Histology of an osteon Spongelike appearance formed by rods Spongy Bone and plates of bone called trabeculae spaces filled with red bone marrow Trabeculae have few osteons or haversian canals Provides strength with little weight no osteocyte is far from blood of bone marrow trabeculae develop along bone's lines of stress Soft tissue that occupies the medullary cavity of a long bone or the spaces amid the trabeculae of spongy bone Red marrow looks like thick blood mesh of reticular fibers and immature cells hemopoietic means produces blood cells in adults found in axial skeleton & girdles Yellow marrow fatty marrow of long bones in adults Gelatinous marrow yellow marrow replaced with reddish jelly Bone Marrow How are bones formed? Intramembranous (Dermal) Broad, flat bones Bones of the skull Scapula Endochondral Long bones Humerus Tibia Intramembranous Ossification Produces flat bones of skull & clavicle Steps of the process mesenchyme condenses into a sheet of soft tissue transforms into a network of soft trabeculae osteoblasts gather on the trabeculae to form osteoid tissue (uncalcified bone) calcium phosphate is deposited in the matrix transforming the osteoblasts into osteocytes osteoclasts remodel the center to contain marrow spaces & osteoblasts remodel the surface to form compact bone mesenchyme at the surface gives rise...
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