Updated: 6/15/2021

Bone Matrix

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  • composition of bone
    • 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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Flashcards (5)
Cards
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Questions (3)

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

QID: 4754
1

Type I collagen

38%

(1868/4969)

2

Osteocalcin

20%

(972/4969)

3

Proteoglycans

38%

(1908/4969)

4

Osteonectin

2%

(124/4969)

5

Osteopontin

1%

(69/4969)

L 1 C

Select Answer to see Preferred Response

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

QID: 399
1

It is the most prevalent non-collagenous protein in bone

18%

(422/2375)

2

It is expressed by mature osteoblasts

11%

(258/2375)

3

It is considered a marker for osteoblast differentiation

13%

(303/2375)

4

It is a glycoprotein that binds calcium

38%

(904/2375)

5

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

20%

(470/2375)

L 4 D

Select Answer to see Preferred Response

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

QID: 1024
1

It is the most abundant noncollagenous protein of bone

10%

(183/1896)

2

It is secreted by osteoclasts

66%

(1247/1896)

3

It is involved in mediating calcium homeostasis

9%

(164/1896)

4

It has been used as a biochemical marker of bone formation

7%

(132/1896)

5

It is part of the organic matrix of bone

8%

(158/1896)

L 1 D

Select Answer to see Preferred Response

Evidence (3)
VIDEOS & PODCASTS (1)
EXPERT COMMENTS (11)
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