2 Bone development, growth, and repair

Question 1

Describe the 2 types of bone development in the embryo

Answer 1

2 types:

• Intramembranous
• Endochondral

Both involve replacing a connective tissue template

Question 2

Describe Intramembranous bone development in the embryo

Answer 2

Sheets of mesenchymal cells (template)

• Differentiation occurs to osteoblasts in centres of ossification. These then merge to form trabecular bone, that is later remodelled
• Remaining mesenchyme makes bone marrow and periosteum (edges - lining)

e.g. can be seen in flat bones of skull, maxilla, and mandible

Question 3

Describe Endochondral bone development in the embryo

Answer 3

Cartilage template
- blood supply to the shaft of the bone (diaphysis - middle) - causes osteoblast differentiation: these are the Primary Centres of Ossification

At birth, the blood supply to the epiphysis (ends of the bone) instigate Secondary Centres of Ossification
- Cartilage growth plate remains to allow the bone to lengthen

e.g. can be seen in long bones and base of the skull

Question 4

Describe the steps involved in Endochondral Ossification

Answer 4

1. Chondrocytes at the centre of the growth cartilage model enlarge, and then die as the matrix calcified
2. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone
3. Blood vessels penetrate the cartilage. New osteoblasts from a primary ossification centre (diaphysis)
4. The bone of the shaft thickens, and the cartilage near each epiphysis is placed by shafts of bone
5. Blood vessels invade the epiphysis, and osteoblasts form the secondary centres of ossification

Question 5

Describe where this last stage of endochondral ossification

Answer 5

At the tip of the bone (epiphysis), there is hyaline cartilage (for smooth joint articulation)
- the secondary centre of ossification occurs below the epiphysis

Below this is the quiescent zone and then the growth plate

Question 6

Name the stages of cell development occuring at the growth plate

Answer 6

1. Zone of resting cartilage
2. Zone of proliferating cartilage
3. Zone of hypertrophic cartilage
4. Zone of calcified cartilage

Question 7

Describe the events that occur during the stages of cell development at the growth plate

Answer 7

1. Zone of resting cartilage
   - Consisting of a hyaline cartilage pad made of inactive cartilage pad made of inactive choncrocytes
   - this zone anchors to the plate to the epiphysis
2. Zone of proliferating cartilage
   - The mitotic proliferation of chondrocytes in this zone pushes the resting cartilage outward
   - heling to lengthen the diaphysis
3. Zone of hypertrophic cartilage
   - in this zone, chondrocytes are stimulated to mature and enlarge
   - helping to lengthen the diaphysis
4. Zone of calcified cartilage
   - the thin zone of dying and dead cartilage cells cement the epiphyseal plate to the diaphysis

Osteoclasts remove the calcified cartilage and make way for osteoblasts to build new spongy bone trabeculae