bone remodelling

Question 1

facts about bone remodelling

Answer 1

• bones are constantly being remodelled
• about 5% of all bone surfaces have active osteoblast activity at any one time
• repair breaks/ other injuries
• repair microfractures from everyday stresses
• change in response to external stresses such as exercise

Question 2

order of remodelling

Answer 2

1. bone lining cells
2. osteoid
3. new bone
4. cement line
5. old bone

Question 3

role of bone remodelling in calcium homeostasis

Answer 3

• bone stores 99% of total body calcium
• remodelling help tightly regulate blood plasma levels
• small changes in Ca in blood can be fatal
• essential for nerve and muscle function, blood clotting and numerous enzymes

Question 4

bone growth- length

Answer 4

• occurs at epiphysial plate
• involves division of chondrocytes
  -stops around 18-25 years of age
• in adults the epiphyses cartilage is replaced by bone& leaves an epiphyseal line
• can be hard to see in older patients due to remodelling

Question 5

overview bone growth- thickness

Answer 5

• occurs at bone surface
• involves secretion and deposition of bone matrix by osteoblasts

Question 6

bone growth- thickness

Answer 6

• osteoblasts lay down bone matrix
• results in a groove forming alongside periosteal blood vessel
• becomes a tunnel containing the vessel
• remodelled and forms a new osteon
• new outer circumferential lamellae is laid out

Question 7

factors affecting bone growth

Answer 7

• dietary intake (Ca, P and vitamin D)
• hormones (insulin-like growth hormone, thyroid hormones, insulin, parathyroid hormone, calcitonin)
• oestrogen shuts down growth at epiphyseal plate
• physical activity (reduced growth- osteopenia)
• genetics (osteoporosis)

Question 8

initial formation of bone tissue

Answer 8

initially comprised of mesenchyme in general shape of bones
2 patterns of bone formation : intramembranous ossification and endochondral ossification

IO= forms flat bones of skull, mandible and clavicles
EO= forms most bones

Question 9

intramembranous ossification

Answer 9

formation of bone within membrane like layers of mesenchyme
- cells of mesenchyme cluster together
- differentiate into osteoprogenitor cells which differentiate into osteoblasts

Question 10

steps of IO

Answer 10

1. development of centre of ossification
2. calcification
3. formation of trabeculae
4. development of the periosteum

Question 11

endochondrial ossification

Answer 11

replacement of cartilage with bone
- mesenchyme forms general shape of bone
- develop into chondroblasts which secrete cartilage ECM
- produce cartilage model (hyaline)

Question 12

EO steps

Answer 12

1. development of cartilage model
2. growth of cartilage model
3. development of primary ossification centre, bone replaces cartilage
4. development of secondary ossification centre
5. formation of articular cartilage and epiphyseal plate