6.7 - The Skeleton & Bone Tissue - Bone Growth and Repair

Question 1

When does ossification begin and end?

Answer 1

Begin: During embryonic development
End: Death

Question 2

What are the two methods of ossification?

Answer 2

• Intramembranous
• Endochondral

Question 3

Where is intramembranous ossification mainly seen?

Answer 3

Flat and irregular bones of the skull

Question 4

How are minerals sourced for ossification during foetal development?

Answer 4

From the bloodstream of the mother

Question 5

Describe intramembranous ossification

Answer 5

1. Mesenchymal stem cells differentiate into the “bone world”, forming osteprogenitor cells and then osteoblasts that form the centre of ossification
2. Some osteoblasts become buried in their own bone deposits, becoming osteocytes. Osteocytes and osteoblasts promote calcification that hardens bone.
3. Blood vessels grow into area, bringing osteoclasts with them. These osteoclasts begin to carve out trabeculae.
4. Continued bone remodelling, trying to form “perfect” bone. Periosteum and endosteum also form.

Question 6

What is interstitial growth?

Answer 6

Growth from within a solid material (e.g. cartilage)

Question 7

What is appositional growth?

Answer 7

Think: deposit

Adding more onto the outside

Question 8

What triggers ossification at bone edges during endochondral ossification?

Answer 8

Bursting of chondrocytes at centre of hyaline cartilage model, leaking cell contents and changing pH, thus causing blood vessels to come to the area.

Question 9

What system regulates bone growth? Provide an example of two common instances of this

Answer 9

Hormonal; testosterone vs oestrogen

Question 10

Which type of bone growth corresponds to increase in length/width?

Answer 10

Length: Interstitial
Width: Appositional

Question 11

When does appositional bone growth finish?

Answer 11

Death

Question 12

When does interstitial bone growth finish?

Answer 12

When growth plates stop dividing

Question 13

Describe appositional growth

Answer 13

Osteoprogenic cells in the peiosteum differentiate into osteoblasts. These osteoblasts lay down new bone, and then bury themselves in bone deposits until they are force to become osetocytes.

Question 14

What is osteoid?

Answer 14

The foundation of bone; created by osteoblasts

Question 15

List four factors that influence bone remodelling

Answer 15

• Hormones
• Nutrition
• Disease
• Motility