Updated: 10/10/2016

Bone Matrix

Topic
Review Topic
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Questions
4
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Evidence
1
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https://upload.orthobullets.com/topic/9003/images/HA_moved.jpg
https://upload.orthobullets.com/topic/9003/images/Type I collagen_moved.jpg
Introduction
  • Bone is made up of
    • organic component
      • 40% of dry weight
    • inorganic component
      • 60% of dry weight
Organic component
  • Components include
    • collagen
      • 90% of organic component
      • primarily type I collagen
      • provides tensile strength
      • it is a triple helix composed of one alpha-2 and two alpha-1 chains
    • proteoglycans
      • responsible for compressive strength
      • inhibit mineralization
      • composed of glycosaminoglycan-protein complexes
    • matrix proteins
      • includes noncollagenous proteins
      • function to promote mineralization and bone formation
        • three main types of proteins involved in bone matrix
          • osteocalcin
            • most abundant non-collagenous protein in the matrix (10%-20% of total) 
              • produced by mature osteoblasts 
            • function
              • promotes mineralization and formation of bone
                • directly involved in regulation of bone density
                • attracts osteoclasts
            • signaling
              • stimulated by 1,25 dihydroxyvitamin D3
              • inhibited by PTH
            • clinical application
              • marker of bone turnover
                • can be measured in urine or serum
          • osteonectin
            • secreted by platelets and osteoblasts
            • function
              • believed to have a role in regulating calcium or organizing mineral in matrix
          • osteopontin
            • function
              • cell-binding protein
    • cytokine and growth factors
      • small amounts present in matrix
      • aid in bone cell differentiation, activation, growth, and turnover
      • include
        • IL-1, IL-6, IGF, TGF-beta, BMPs
Inorganic component
  • Components include
    • calcium hydroxyapatite (Ca10(PO4)6(OH)2  
      • provides compressive strength
    • osteocalcium phosphate (brushite)
 

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Questions (4)

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(OBQ13.119) Which of the following components of bone is most responsible for compressive strength? Review Topic

QID: 4754
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1

Type I collagen

38%

(1618/4308)

2

Osteocalcin

20%

(878/4308)

3

Proteoglycans

38%

(1621/4308)

4

Osteonectin

2%

(104/4308)

5

Osteopontin

1%

(63/4308)

L 5

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(OBQ08.13) All of the following are true regarding osteocalcin EXCEPT which of the following? Review Topic

QID: 399
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1

It is the most prevalent non-collagenous protein in bone

18%

(355/2009)

2

It is expressed by mature osteoblasts

11%

(216/2009)

3

It is considered a marker for osteoblast differentiation

12%

(249/2009)

4

It is a glycoprotein that binds calcium

39%

(783/2009)

5

Higher levels are correlated with increases in bone mineral density during osteoporosis treatment

19%

(389/2009)

L 4

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SUBMIT RESPONSE 4

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(OBQ05.138) All of the following statements are true of osteocalcin EXCEPT: Review Topic

QID: 1024
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1

It is the most abundant noncollagenous protein of bone

8%

(115/1512)

2

It is secreted by osteoclasts

69%

(1047/1512)

3

It is involved in mediating calcium homeostasis

8%

(126/1512)

4

It has been used as a biochemical marker of bone formation

7%

(102/1512)

5

It is part of the organic matrix of bone

7%

(112/1512)

L 2

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SUBMIT RESPONSE 2

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(OBQ05.70) Ca10(P04)6(OH)2 is the chemical formula of Review Topic

QID: 956
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1

Calcium hydroxyapatite

83%

(286/346)

2

Osteocalcium phosphate

1%

(4/346)

3

Calcium pyrophosphate

15%

(52/346)

4

Osteocalcin

0%

(1/346)

5

Polymethylmethacrylate

1%

(3/346)

L 1

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SUBMIT RESPONSE 1
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