Bone Ossification

Question 1

2 types of growth

Answer 1

Interstitial
Appositional

Question 2

Interstitial growth

Answer 2

Usually in soft tissues
Expands from inside out

Question 3

Appositional growth

Answer 3

In bones
Growth from cell surface

Question 4

Which bones are formed by intramembranous ossification

Answer 4

Flat bones

Question 5

Intramembranous ossification in flat bones

Answer 5

Condensation of mesenchymal cells which form a flat sheet
Forms straight into bone no cartilage
Osteoblasts precursors form on surface
Differentiation into mature active osteoblasts
Osteoid formation
Mineralisation and incorporation of osteocytes
Further osteoid formation

Question 6

Endochondral ossification at growth plate

Answer 6

The distal growth plate end has resting zone cells which can proliferate and become layers of active chondrocytes - germinal zone

Chondrocytes replicate and are all close together. Chondrocytes secrete extracellular matrix (osteoid) which leads to interstitial growth and pushes matrix apart, cells get further apart = hypertrophic zone, leading to lengthening of bone

With time, cells die and degenerate = degenerative zone

Cartilage gets mineralised then osteoclasts/chondroclast resorb calcified cartilage and chew away mineralised matrix . Bone apposition occurs

Question 7

Germinal zone

Answer 7

Distal growth plate has resting zone cells which can proliferate and become layers of active chondrocytes

Question 8

Hypertrophic zone

Answer 8

Chondrocytes replicate and are all close together
Chondrocytes secrete extracellular matrix (osteoid) which leads to interstitial growth and pushes matrix cells apart
Leads to lengthening of bone

Question 9

Degenerative zone

Answer 9

With time cells die and degenerate at growth plate

Question 10

How are long bones formed

Answer 10

Endochondral ossification