Bone mineralization

Question 1

List the organic material in bone composition

Answer 1

• Cell
• Collagen
• Glycosaminoglycans
• Proteoglycans and proteins

Question 2

List the inorganic material in bone composition

Answer 2

• Hydroxyapatite

- Calcium carbonate

Question 3

Describe intramembranous ossification

Answer 3

Formed directly in loose mesenchyme from an osteoblast-secreting scaffold and matrix vesicles, then calcifying:

• Bone that are constantly undertension
• Irregular bones (e.g. Skull bones)

Question 4

Describe endochondral ossification

Answer 4

Formed from the replacement of a hyaline cartilage model. Primary and secondary ossification centres form:

• Bones that are needed to perform immediately and are constantly under pressure
• Long bones (e.g. long bones)

Question 5

Describe osteoclast/osteoblast activity balance

Answer 5

Osteoblasts secrete RANKL and a decoy protein (OPG) that binds with the RANKL. If PTH is present, the decoy protein product is blocked. This allows the RANKL to bind with RANK receptors on pre-osteoclasts.

• RANK receptors trigger production and maturation of osteoclasts.
• PTH triggers osteoclast activity, by binding decoy protein (OPG)
• This ensures that osteoclastic activity only occurs in the presence of active osteoblasts.
• This ensure that osteoblastic activity always matches osteoclastic activity.

Question 6

Clinically, how do you get net loss of bone during inflammation?

Answer 6

Inflammation and bacteria intermediates bind directly to the RANK receptor and activate the RANK cascades but not through the osteoblasts.
- Trigger osteoclast activity, disproportionally to osteoblast activity.
Since osteoblast/osteoclast activity is so linked, replacement of loss of bone is slow and often permanent.