1.96 Bone Growth

Question 1

What are osteoprogenitor cells?

Answer 1

Stem cells

Can differentiate into other bone cell types

Question 2

What are osteoblasts?

Answer 2

Synthesise the organic bone matrix (secrete collagen to form osteoid)
• Hormones act on osteoblasts, which in turn regulate osteoclastic activity
• Osteoblasts produce osteoid component of mineralised bone matrix
As matrix is laid down osteoblasts become trapped within bone – osteocytes in lacunae

Question 3

What are osteocytes?

Answer 3

Inactive (mature) osteoblasts

Become trapped in mineralised bone

Question 4

What are osteoclasts?

Answer 4

Erode mineralised bone and remodel
Found on the surface of sites of bone resorption
They secerete things that erode the mineralised bone and remodel it into different shapes

Question 5

What forms osteoclasts?

Answer 5

Blood monocytes - immune cells

Question 6

What do osteoclasts secrete?

Answer 6

Osteoclasts secrete H+ and Cl- ions to create acidic environment for solubilising bone matrix - acidic enviroment
Osteoclasts then secrete Cathepsin K protease into subosteoclastic compartment to degrade collagen and proteins

Question 7

What stimulates and inhibits osteoclast inhibition?

Answer 7

Process can be stimulated by parathyroid hormone (PTH) and inhibited by calcitonin

Question 8

Which bone type is present during bone development?

Answer 8

• During bone development, cartilage matrix is coated with woven bone
• Woven bone is eroded by osteoclast activity and remodelled

Question 9

What are the processes involved in bone formation?

Answer 9

Ossification - bone formation

Mineralisation - addition of hydroxyapatite

Question 10

What can bone formation defects result in?

Answer 10

Ossification defect - osteogenesis imperfecta - fragile bones - small stature in severe cases
Mineralisation defects - Rickets (childhood) - osteomalacia (adults)

Question 11

What are the two methods of ossifications?

Answer 11

Intramembranus, and intrachondral

Question 12

What is intramembronous ossification?

Answer 12

connective tissue membrane to bone
○ Condensation of mesenchyme forms bone blastema
○ Osteoblast and osteoclast activity
○ Formation of flat bone from a membranous mesenchyme template
E.g. skull bones, mandible, clavicle

Question 13

What is endochondral ossification?

Answer 13

cartilage to bone
○ Formation of bone from a cartilage template
○ Most bones form this way
Involves chondrocytes and bone cells

Question 14

What is the process of intramembronous ossification?

Answer 14

1. Mesenchymal cells form a membrane and differentiate into osteoblasts
2. Ossification centre froms in the middle
3. Osteoblasts secrete osteoid
4. Froms mineralised bone matrix in specules (spikes)
5. Osteoblasts become trapped in extracellular matrix and become osteocytes
6. Blood vessels form
7. Osteoid laid down between specula which form the trabeculae of woven bone
8. Mesenchyme forms the periosteum
9. Woven bone forms collar then is remodelled to haversion bone

Question 15

What is the process of endochondral ossification?

Answer 15

1. Chondroblasts form perichondrium and then periosteum
2. Formation of bone collar
3. Chondrocyte proliferation increases length of template
4. Cavitation of cartilage template
5. Primary ossification centre forms in cavity
6. Calcium deposited in cartilage matrix in primary ossification centre and chondrocytes proliferate further
7. Increases bone length and width
8. Capillaries penetrate periosteum and grow into diaphyses
9. Secondary ossification centres established in epiphyses