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Chapter 4. Bone

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The micrograph below shows an image of bone forming in the diaphysis (shaft) of an embryonic canine limb bone. Refer to the image when answering the following questions.

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Image not available.

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What site indicates cells that are most responsible for maintaining the bony matrix in adult bone?

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A. A

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B. B

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C. C

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D. D

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E. E

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The answer is C: Osteocytes are the main resident cells in mature bone. Osteocytes sit in lacunae in the matrix that they maintain.

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The micrograph below shows an image of bone forming in the diaphysis (shaft) of an embryonic canine limb bone. Refer to the image when answering the following questions.

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Image not available.

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What site indicates cells that are most responsible for enlarging the marrow cavity in the diaphysis as long bones grow?

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A. A

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B. B

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C. C

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D. D

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E. E

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The answer is D: Osteoclasts are large, multinucleated cells that are responsible for the removal and turnover of bone matrix. As bones grow and the diaphysis expands in width by intramembranous ossification (as seen in this image), osteoclasts enlarge the marrow cavity.

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The micrograph below shows an image of bone forming in the diaphysis (shaft) of an embryonic canine limb bone. Refer to the image when answering the following questions.

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Image not available.

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What is the predominant type of collagen in the area marked with an asterisk?

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A. Type I collagen

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B. Type II collagen

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C. Type III collagen

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D. Type IV collagen

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E. Type X collagen

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The answer is A: The asterisk marks an area of osteoid, the organic components of newly deposited bone matrix. Type I collagen constitutes 90% of the organic material in bone matrix.

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Osteopetrosis is a rare condition produced by defects in the activity of osteoclasts. Modeling and remodeling normally does not occur in patients with osteopetrosis, which results in thick, misshapen bones. What defect in osteoblasts could result in the development of osteopetrosis?

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A. Gain-of-function mutation in the gene encoding the ...

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