Bone: structure and function

Question 1

Define ‘compact bone’

Answer 1

• Bone made of Haversian canal
• Mostly mineralized tissue
• highly ordered
• No bone marrow
• Outer layer of all bone structures
• Resistant to bending and breaking

Question 2

Define ‘cancellous bone’

Answer 2

• Just layers of bone but less structured (no Haversian canal
• Bone marrow and mineralized tissue
• Trabeculae = struts in bone
• inner layer of bone structures
• Vulnerable to fracture

Question 3

List the types of bone and their distribution throughout the skeleton

Answer 3

Compact bone:

• Limbs
• skull

Cancellous bone:

• Vertebrae
• Ribs

Question 4

Describe the composition of bone matrix

Answer 4

Compositions of bones:
Proteins:
- Collagen (type 1): gives bone tensile strength
- Non-collagenous proteins: 
1) alkaline phosphatase
2) Proteoglycans
3) growth factors

Mineral:

• Hydroxyapatite = crystal of calcium and phosphate
• Gives bone compressive strength

Question 5

Describe osteoblasts

Answer 5

• Bone forming cells
• Round
• Synthesize bone matrix
• Mineralized matrix

Question 6

Define ‘lining cells’

Answer 6

• flattened osteoblasts

- Line bone surfaces

Question 7

Define ‘osteocytes’

Answer 7

• Embedded in bone matrix
• Connect to each other via canaliculae
• sense mechanical forces

Question 8

Define ‘osteoclasts’

Answer 8

• Bone resorbing cells
• Multinucleated giant cells (derived from monocytes)
• Dissolve mineral and degrade protein
• Release embedded growth factors from bone (ensure osteoclastic and osteoblastic activity matches)

Question 9

Why does bone turnover?

Answer 9

• Shape changes in bone
• Change in bone loading
• Repairing microdamage

Question 10

Describe osteoblast and osteoclast activity

Answer 10

Coupled activity -> bone formation and remodelling are balanced.
Growth factors are embedded in bone:
- Osteoclastic activity causes release of GF
- GF causes osteoblast differentiation

RANK-RANKL Binding

• Osteoblasts have RANKL on surface
• RANKL binds with RANK receptor on pre-osteocytes ( to cause osteoclast differentiation.
• Osteo-protegerin: “decoy” RANK receptor that binds and blocks RANKL