16 Bone Function And Repair

Question 1

What are the 3 bone functions?

Answer 1

Mechanical
Synthetic (haemopoeisis)
Metabolic (mineral storage, fat storage)

Question 2

What is endochondral ossification?

Answer 2

Formation of long bones from cartilage template

Continued lengthening is by ossification at epiphesial plates

Question 3

What is intra-membranous ossification?

Answer 3

Formation of bone from clusters of mesenchymal stem cells in centre of bone
Interstitial growth
Occurs within condensations of mesenchymal tissue

Question 4

Stages of intramembranous ossification in flat bone

Answer 4

1. Mesenchymal stem cells (MSCs) form a tight cluster
2. MSCs transform into osteoprogenitor cells, then transform into osteoblasts
3. Osteoblasts lay down osteoid
4. Osteoid mineralises to form rudimentary bone tissue spicules
5. Spicules join to form trabeculae, merge to from woven bone
   Trabeculae replaced by lamellar of mature compact bone

Question 5

What is osteoid?

Answer 5

Extracellular matrix containing Type 1 collagen

Question 6

What is absent in cancellous bone but present in compact bone?

Answer 6

Haversian and volkmanns canals which carry blood vessels, lymph vessels and nerves

Question 7

How do bones resist fracture?

Answer 7

Has great tensile and compressive strength
Has degree of flexibility
Main force lines are through cortical (compact) bone

Question 8

How does activity of osteocytes affect bone stability?

Answer 8

Can act like osteoblasts and lay down osteoid into their lacunae
Can act like osteoclasts and degrade bone (osteocytic osteolysis)
Increased by oestrogen, thyroid hormones, PTH

Question 9

How can the activity of osteoblasts affect bone stability?

Answer 9

Bone deposition

Stimulated by calcitonin, GH, oestrogen and testosterone, thyroid hormones and vitamin A

Question 10

How does the activity of osteoclasts affect bone stability?

Answer 10

Bone reabsorption
Calcitonin blocks action of PTH at the PTH receptor
Increased by PTH - releases calcium ions into blood

Question 11

What are the stages of fracture repair?

Answer 11

1. Haematoma formation
2. Fibrocartilaginous callus formation
3. Bone callus formation
4. Bone remodelling

Question 12

What happens in haematoma formation in fracture repair?

Answer 12

Blood clot formed in which granulation tissues arises
Bone cells at fracture edge die
Swelling
Phagocytose cells and osteoclasts begin to remove dead and damaged tissue
Macrophages eventually remove blood clot

Question 13

What happens in fibrocartilginous callus formation in fracture repair?

Answer 13

Procallus of granulation tissue replaced by a firbocartilaginous callus in which bone trabeculae are developing
New blood vessels infiltrate haematoma
Fibroblasts produce collagen fibres that span break

Question 14

What happens in bony callus formation in fracture repair?

Answer 14

Endochondral and intramembranous ossification give rise to bony callus of cancellous bone
Trabeculae develop

Question 15

What happens in bone remodelling in fracture repair?

Answer 15

Cancellous bone is replaced by compact cortical bone until remodelling is complete

Question 16

What increases the susceptibility to fracture?

Answer 16

Loss of mass within the trabecular bone

Question 17

Osteogenesis imperfecta

Answer 17

Mutation in COL1A gene
Incorrect production of collagen 1 fibres
Weak bone and increased fracture risk
Shortened height and stature
Mainly affects neonates and children
Blue sclera

Question 18

Rickets

Answer 18

Mainly affects children
Vitamin D deficiency
Poor calcium mobilisation
Ineffective mineralisation
Weakened bone development
Soft bones
Bowed legs

Question 19

Osteomalacia

Answer 19

‘Rickets’ in adult
Vitamin D deficiency
Increased calcium reabsorption
Can be caused by kidney disease, protection from sunlight, surgery on stomach/intestine, certain drugs

Question 20

Osteoporosis primary type 1

Answer 20

Occurs in postmenopausal women
Increased osteoclast number
Caused by loss of oestrogen

Question 21

Osteoporosis primary type 2

Answer 21

Occurs in older men and women
Due to loss of osteoblast function
Loss of both oestrogen and androgen

Question 22

Osteoporosis secondary

Answer 22

Result of drug therapy
Processed agent bone remodelling (malnutrition, prolonged immobilisation weightlessness)
Metabolic bone diseases

Question 23

What does osteoporosis lead to?

Answer 23

Incomplete filling of osteoclast reabsorption bays

Question 24

Achondroplasia

Answer 24

Inherited mutation in FGF3 receptor gene
FGF promotes collagen formation from cartilage
Endochondral ossification affected
Intra-membranous ossification unaffected
Results in short stature but normal sized head and torso