Ossification

Question 1

What are the 2 types of ossification?

Answer 1

1. Intramembranous

2. Endochondral

Question 2

What is ossification?

Answer 2

Formation of bones by the replacement of pre-existing CT

Question 3

What bones are formed from intramembranous ossification?

Answer 3

Flat bones e.g. cranial bones

Question 4

How many stages are there in intramembranous ossification?

Answer 4

4

Question 5

What occurs at stage 1 of intramembranous ossification?

Answer 5

• Mesenchymal cells differential into osteoblasts

- Cluster of osteoblasts form ossification centre

Question 6

What is the function of an ossification centre?

Answer 6

Lay down osteoid

Question 7

What occurs at stage 2 of intramembranous ossification?

Answer 7

• Mineralisation of osteoid to produce island of bone

- Trapped osteoblasts become osteocytes

Question 8

What occurs at stage 3 of intramembranous ossification?

Answer 8

• Islands of bone join to form trabeculae

- Mesenchyme cells at edges condense to form periosteum

Question 9

What occurs at stage 4 of intramembranous ossification?

Answer 9

• Red marrow develops from mesenchymal cells in trabecular spaces

Question 10

What bones are formed from endochondral ossification?

Answer 10

Long bones of the body

Question 11

How many stages are involved in endochondral ossification?

Answer 11

5

Question 12

Why is endochondral ossification called so?

Answer 12

Involves the ossification of a hyaline cartilage template

Question 13

What makes up the hyaline cartilage template involved in endochondral ossification?

Answer 13

Hyaline deposited in the shape of the bone within a mass of mesenchymal tissue

Question 14

What occurs at stage 1 of endochondral ossification?

Answer 14

• Cartilage cells in central diaphysis die to leave cavities

- Perichondrium produces osteoblasts which lay down bone collar by IM ossification

Question 15

What occurs at stage 2 of endochondral ossification?

Answer 15

• Cartilage matrix in centre continues to deteriorate
• Diaphysis diameter increases by bone deposition on outside and resorption on inside
• Chondrocytes in bone multiply, increasing length and breadth

Question 16

What occurs at stage 3 of endochondral ossification?

Answer 16

• Capillaries penetrate diaphysis carrying in osteoprogenitor cells
• Osteoprogenitor cells become osteoblasts and set up primary ossification centre
• Bone laid down to replace lost cartilage in centre

Question 17

What occurs at stage 4 of endochondral ossification?

Answer 17

• Capillaries penetrate epiphyses of bone
• Osteoprogenitor cells pulled into epiphyses and produce secondary ossification centres
• Formation of medullary cavity

Question 18

When does stage 4 of endochondral ossification occur?

Answer 18

Approx. at birth

Question 19

What occurs at stage 5 of endochondral ossification?

Answer 19

• Ossification of epiphysis is complete

- Cartilage only remains in epiphyseal growth plate and articular cartilage

Question 20

What are the 5 zones of the epiphyseal growth plate?

Answer 20

1. Resting
2. Proliferate
3. Hypertrophic
4. Ossifying Cartilage
5. Bone Deposition

Question 21

What occurs in the hypertrophic zone?

Answer 21

Osteoblasts get bigger and begin to calcify

Question 22

What is the weakest part of the skeleton?

Answer 22

Joints