Bones- Are calcified connective tissue consisting of cells (osteocytes ) in a matrix of ground substance and collagen fibers.
- Serve as a reservoir for calcium and phosphorus and act as levers on which muscles act to produce the movements permitted by joints.
- Contain internal soft tissue, the marrow , where blood cells are formed.
- Are classified, according to shape, into long, short, flat, irregular, and sesamoid bones; and according to their developmental history into endochondral and membranous bones.
Long Bones
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- Include the humerus, radius, ulna, femur, tibia, fibula, metacarpals, and phalanges.
- Develop by replacement of hyaline cartilage plate (endochondral ossification ).
- Have a shaft (diaphysis ) and two ends (epiphyses ). The metaphysis is a part of the diaphysis adjacent to the epiphyses.
Diaphysis
- Forms the shaft (central region) and is composed of a thick tube of compact bone that encloses the marrow cavity.
Metaphysis
- Is a part of the diaphysis, the growth zone between the diaphysis and epiphysis during bone development.
Epiphyses
- Are expanded articular ends , separated from the shaft by the epiphyseal plate during bone growth, and composed of a spongy bone surrounded by a thin layer of compact bone.
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| Short Bones |
- Include the carpal and tarsal bones and are approximately cuboid shaped.
- Are composed of spongy bone and marrow surrounded by a thin outer layer of compact bone.
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| Flat Bones |
- Include the ribs, sternum, scapulae, and bones in the vault of the skull.
- Consist of two layers of compact bone enclosing spongy bone and marrow space
- Have articular surfaces that are covered with fibrocartilage.
- Grow by replacement of connective tissue.
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| Irregular Bones |
- Include bones of mixed shapes such as bones of the skull, vertebrae, and coxa.
- Contain mostly spongy bone enveloped by a thin outer layer of compact bone.
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| Sesamoid Bones |
- Develop in certain tendons and reduce friction on the tendon, thus protecting it from excessive wear.
- Are commonly found where tendons cross the ends of long bones in the limbs, as in the wrist and the knee (i.e., patella).
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