http://upload.orthobullets.com/topic/9003/images/HA_moved.jpg
http://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)
 

Please rate topic.

Average 3.7 of 20 Ratings

Questions (4)

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

QID:4754
1

Type I collagen

40%

(920/2299)

2

Osteocalcin

22%

(504/2299)

3

Proteoglycans

34%

(784/2299)

4

Osteonectin

2%

(44/2299)

5

Osteopontin

2%

(35/2299)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

Proteoglycans, in addition to calcium hydroxyapatite [Ca10(PO4)6(OH)2], are most responsible for providing compressive strength.

Bone is composed of both organic and inorganic components. Inorganic components include calcium hydroxyapatite and osteocalcium phosphate. Organic components include collagen, proteoglycans, matrix proteins, cytokines and growth factors. While Type I collagen is responsible for providing the tensile strength of bone, proteoglycans and calcium hydroxyapatite [Ca10(PO4)6(OH)2] are most responsible for providing compressive strength. Proteoglycans contain a core protein with various numbers of covalently attached side chains of glycosaminoglycans. In addition to providing compressive strength, they are also responsible for binding growth factors and inhibiting mineralization.

Knothe et al. review the osteocyte. They discuss that osteocytes are the most abundant cells in bone, are actively involved in maintaining the bony matrix, and may act as mechanosensors.

Illustration A shows a proteoglycan aggregate, which can form when individual molecules link onto a chain of hyaluronic acid.

Incorrect Answers:
Answer 1: Type I collagen is responsible for the tensile strength of bone.
Answer 2: Osteocalcin is the most abundant non-collagenous protein in the matrix and promotes the mineralization and formation of bone.
Answer 4: Osteonectin is believed to have a role in regulating calcium or organizing mineral in matrix.
Answer 5: Osteopontin is a cell-binding protein.

ILLUSTRATIONS:

Please rate question.

Average 2.0 of 20 Ratings

Question COMMENTS (4)

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

QID:399
1

It is the most prevalent non-collagenous protein in bone

16%

(237/1454)

2

It is expressed by mature osteoblasts

11%

(153/1454)

3

It is considered a marker for osteoblast differentiation

11%

(161/1454)

4

It is a glycoprotein that binds calcium

42%

(611/1454)

5

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

19%

(280/1454)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

Pure fact question from basic science. “Osteocalcin is the most prevalent noncollagenous protein in bone” (from Miller's Review). It is expressed by mature osteoblasts and is a marker of osteoblast differentiation. Osteocalcin is the most specific marker of the osteoblast phenotype and is expressed only in mature osteoblasts. During osteoporosis treatment, serum levels correlate with increases in bone mineral density. Osteonectin, not osteocalcin, is a glycoprotein that binds calcium.


Please rate question.

Average 3.0 of 32 Ratings

Question COMMENTS (0)

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

QID:956
1

Calcium hydroxyapatite

87%

(171/197)

2

Osteocalcium phosphate

1%

(2/197)

3

Calcium pyrophosphate

11%

(22/197)

4

Osteocalcin

1%

(1/197)

5

Polymethylmethacrylate

1%

(1/197)

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

The chemical structure of hydroxyapatite is Ca10(PO4)6(OH)2. Hydroxyapatite is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. Up to 50% of bone by weight is made up of a modified form of hydroxyapatite. It is one of few materials that will support bone ingrowth and osseointegration when used in orthopaedic, dental and maxillofacial applications.


Please rate question.

Average 1.0 of 66 Ratings

Question COMMENTS (0)

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

QID:1024
1

It is the most abundant noncollagenous protein of bone

7%

(90/1312)

2

It is secreted by osteoclasts

70%

(921/1312)

3

It is involved in mediating calcium homeostasis

9%

(112/1312)

4

It has been used as a biochemical marker of bone formation

7%

(88/1312)

5

It is part of the organic matrix of bone

7%

(96/1312)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

Osteocalcin is the most abundant noncollagenous protein in bone. It is secreted by osteoblasts and plays a role in bone mineralization and calcium homeostasis. It is pro-osteoblastic, or bone-building, by nature. It has recently been used as a biochemical marker for bone formation in trials of anabolic drugs, such as forteo. Answer 2 is the false statement because osteocalcin is secreted by osteoblasts.


Please rate question.

Average 3.0 of 20 Ratings

Question COMMENTS (11)
EVIDENCE & REFERENCES (3)
Topic COMMENTS (5)