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The Skeletal System (Chapter 6) (Anatomical and functional properties of…

- - - - Long Bone
        
        longer than they are wide
      - Short Bones
        
        roughly equal
      - Flat Bones
        
        thin and relatively broad
      - Irregular Bone
        
        have complex shapes that do not fit easily into any other category
      - Compact Bone
        
        relatively solid
      - Spongy Bone
        
        resembles a network of bony rods or struts separated by spaces.
  - - - In compact and spongy bone
    - - found between narrow sheets of calcified matrix
    - - calcified matrix
    - - small channels, radiate through the matrix, interconnecting lacunae and linking them to nearby blood vessels
  - - - the basic functional unit of compact bone
    - - contains one or more blood vessels
    - - provides passageways for linking the blood vessels of the central canals with those of the periosteum and the marrow cavity
    - - rods or plates
  - - - mature bone cells. maintain normal bone structure by recycling he calcium salts in the bony matrix around themselves and by assisting in repairs.
    - - giant cells with 50 or more nuclei. Acids and enzymes secreted by osteoclasts dissolve the bony matrix and release the stored minerals through osteolysis, or resorption. This process helps regulate calcium and phosphate concentrations in body fluids
    - - the cells responsible for the production of new bone, a process called osteogenesis, Osteoblasts produce new bone matrix and promote the deposition of calcium salts in the organic matrix. At any moment, osteoclasts are removing matrix and osteoblasts are adding to it. When an osteoblast becomes completely surrounded by calcified matrix
- - - - place where ossification first occurs
  - - - starts when chondrocytes within the cartilage model enlarge and the surrounding matrix begins to calcify. The Chondrocytes die because the diffusion of nutrients slows through the calcifed matrix
    - - Bone formation occurs at the shaft surface. Blood vsesels invade the perichondrium, and calls of its inner layer differentiated osteoblasts that begin producing bone matrix.
    - - Blood vessels invade the inner region of the cartilage, and newly differentiate into osteoblasts form spongy bone within the center of the shaft at a primary ossification center. Bone development proceeds toward either end filling the shaft with spongy bone.
    - - As the bone enlarges, osteoblasts break down some of the spongy bone and create marrow cavity. The cartilage model does not completely fill with bone because the epiphyseal cartilages on the ends continue to enlarge, increasing the length of the developing bone. Although osteoblasts from the shaft continuously invade the epiphyseal cartilages, the bone grows longer because new cartilage continuously added in front of the advacing osteoblasts. This situation is like a pair of joggers, one in front of the other: As long as they run at the same speed, the one in back will never catch the one in front, no matter how fa they travel.
    - - The centers of the epiphyses begin to calcify. As blood vessels and osteoblasts enter these areas, secondary ossification filled with spongy bone. A thin cap of the original cartilage model remains exposed to the joint cavity as the articular cartilage
- - - - A Large blood clot soon forms and closes off the injured blood vessels
    - - cells of the periosteum and endosteum undergo mitosis, and the daughter cells migrate into the fracture zone. There they form localized thickenings, an external callus, and an internal callus
    - - Osteoblasts replace the new central cartilage if the external callus with spongy bone. the external and internal calluses form a continuous brace of spongy bone at the fracture site.
    - - the remodeling spongy bone at the fracture site may continue over a period of 4 months to well over a year. When the remodeling is complete, the fragments of dead bone and the spongy bone of the calluses will be gone.