Bone Matrix

Topic updated on 03/12/14 10:54pm
  • 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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Qbank (4 Questions)

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

1. Type I collagen
2. Osteocalcin
3. Proteoglycans
4. Osteonectin
5. Osteopontin

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

1. It is the most prevalent non-collagenous protein in bone
2. It is expressed by mature osteoblasts
3. It is considered a marker for osteoblast differentiation
4. It is a glycoprotein that binds calcium
5. Higher levels are correlated with increases in bone mineral density during osteoporosis treatment

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

1. Calcium hydroxyapatite
2. Osteocalcium phosphate
3. Calcium pyrophosphate
4. Osteocalcin
5. Polymethylmethacrylate

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

1. It is the most abundant noncollagenous protein of bone
2. It is secreted by osteoclasts
3. It is involved in mediating calcium homeostasis
4. It has been used as a biochemical marker of bone formation
5. It is part of the organic matrix of bone



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