Bone Growth and Development Part 1

Question 1

2. What do both types of bone development in the embryo involve?

Answer 1

Both involve replacing a connective tissue template

Question 2

Describe what intramembranous bone development is

Answer 2

Replacement of bone with bone

Question 3

Describe what endochondral bone development is

Answer 3

Replacement of cartilage with bone

Question 4

Where does the intramembranous bone growth come from

Answer 4

Comes from sheets of mesenchymal cells

Question 5

8. What do mesenchymal cells differentiate into

Answer 5

differentiate into to osteoblasts in centres of ossification

Question 6

What do the osteoblasts merge to form?

Answer 6

merge to form trabecular bone that is remodelled

Question 7

What happens to the remaining mesenchyme (mesenchymal cells) that are not involved in differentiation into osteoblasts?

Answer 7

Remaining mesenchyme makes bone marrow and periosteum

Question 8

What is intramembranous growth most associated with regarding the formation of bones

Answer 8

most associated with flat bones

Question 9

12. What are examples of flat bones that are associated with intramembranous growth

Answer 9

examples of flat bones associated with intramembranous growth are:
- Skull
- Maxilla
- Mandible

Question 10

13. Through what growth plate do long bones grow in length from

Answer 10

Epiphyseal growth plate

Question 11

1. What happens to the epiphyseal growth plate in adulthood

Answer 11

In adulthood the epiphyseal growth plate fuses

Question 12

16. Where does appositional growth occur

Answer 12

At the periosteual surface

Question 13

1. How does appositional growth occur.

Answer 13

Occurs by resorption of bone at the inner periosteual surface, increasing size of medullary cavity and widen the long bone

Question 14

19. Describe the mechanism of endochondral bone growth in long bones

Answer 14

1. Blood supply to shaft of bone causes osteoblast differentiation at the primary centre of ossification
2. At birth blood supply to the epiphysis instigate secondary centres of ossification
3. Cartilage growth plate remains to allow the bone to lengthen

Question 15

Outline the mechanism of endochondral ossification

Answer 15

1. Chondrocytes at the centre of the growing cartilage model enlarge and then die as the matrix calcifies
2. newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone
3. Blood vessels penetrate the cartilage. New osteoblasts then form a primary centre of ossification
4. The bone of the shaft thickens and the cartilage near each epiphysis is replaced by shafts of bone
5. Blood vessels invade the epiphysis and osteoblasts form secondary centres of ossification

Question 16

21. What cells control bone remodelling ?

Answer 16

bone remodelling is controlled by the cells:

• Osteocytes
• Osteoblasts
• Osteoclasts

Question 17

22. What is bone remodelling in response to?

Answer 17

In response to:
- To stresses and strains put upon the bone
- Micro fractures
- Wear and tear of the bone

Question 18

23. Outline the process of bone remodelling

Answer 18

1. Osteocytes detect fracture or stress
2. Osteoclasts are signalled to resorb bone in that region.
3. Osteoclasts then produce acids to break down non organic components of bone. They also take up the organic components of the bone to break them down via lysosomal action.
4. This produces a pit known as Howship’s lacuna
5. Osteoclast leaves and active osteoblasts come in to build and or remodel bone in the howship’s lacuna

Question 19

25. What 4 reasons can adult bone remodelling be increased?

Answer 19

Adult bone remodelling can be increased because of:

• Change in function
• New demands (running, tennis, jumping)
• Repair of fractures
• Disease (e.g. Pagets disease)

Question 20

26. What is the main aim of adult bone remodelling?

Answer 20

The aim is to place bone struts in the location and direction of maximum stress while keeping the structure open to minimise weight

Question 21

27. Where does the growth plate of long bones lie?

Answer 21

In the epiphyseal end of the bone

Question 22

29. What occurs at the diaphyseal end of the growth plate?

Answer 22

chondrocytes mature and die and are replaced by bone

Question 23

32. After space is left when the largest hypertrophic chondrocytes die, what happens?

Answer 23

Osteoclasts resorb the calcified cartilage and then osteoblasts replace it with mineralised bone