bone remodeling

Question 1

bone repair process:

Answer 1

1. osteoblasts sense micrcracks and secrete NF-kB receptor activator ligand (RANKL)
2. RANKL binds to receptors on monocytes
3. monocytes fuse and form multi-nucleated osteoclast cells
4. osteoclasts secrete lysosomal enzymes (i.e. collagenase) to digest the collagen in the matrix, creating surface holes (Howship’s lacunae). also, dissolves hydroxyapatite, releasing Ca and phosphorus
5. osteoblasts secrete osteoprotegerin and deactivates RANKL (slows down osteoclast activity). osteoclast apoptosis.
6. osteoblasts fill in the lacunae with a osteoid seam - calcium and phosphorus forming a new hydroxyapatite
7. some osteoblasts get trapped in lacunae -become osteocytes

Question 2

parathyroid hormone role:

Answer 2

enhances bone resorption

releases parathyroid (PTH) in response to low serum calcium

stimulates RANKL release

bone resorption increases [Ca]

negative feedback

Question 3

what is Wolff’s law?

Answer 3

“bones that bear more weight remodel more”

Question 4

calcitonin role:

Answer 4

inhibits bone resorption
decreases serum calcium

Question 5

vitamin D role:

Answer 5

stimulates intestinal absorption of calcium
increases serum calcium
stimulates calcitonin which inhibits bone resorption

Question 6

what releases calcitonin?

Answer 6

parafollicular cells

Question 7

describe the 2 layers of the periosteum:

Answer 7

outer fibrous layer - protection and tendon attachment

inner cellular layer - progenitor stem cells (osteoblasts, chondroblasts)

Question 8

what are the 2 types of bone of the diaphysis?

Question 9

organic part of lamellar bone:

Answer 9

collagen

Question 10

inorganic part of lamellar bone:

Answer 10

calcium phosphate (hydroxyapatite)

Question 11

what is a Haversian canal?

Answer 11

contains blood supply and innervation
runs through osteons in the cortical, lamellar bone

Question 12

epiphysis composition:

Answer 12

-spongy bone (w/ crosslinking trabeculae) and surrounding bone marrow

-resistant to mechanical stress

Question 13

growth factor that helps stimulate osteoclast formation from monocytes:

Answer 13

MCSF (macrophage colony stimulating factor)

Question 14

what is a Volkmann’s canal?

Answer 14

connects Haversian canals

Question 15

fracture callus formation steps:

Answer 15

1. CLOT: blood clot forms at the fracture site
2. INFLAMMATION: neovascularization and organization of the clot (fibroblasts present). begin to repair the necrotic bone
3. CALLUS: cartilage callus formed and woven bone (half hazard, irregular, but quick bone) is created
4. REMODELING: blasts and clasts produce lamellar (mature) bone. AKA compact bone.

Question 16

characteristics of woven vs lamellar bone:

Answer 16

woven: irregular bone with large osteocytes

lamellar: regular pattern visualized with polarized light

Question 17

what is a comminuted fracture?

Answer 17

fractured in 2 places

Question 18

what is pseudoarthrosis?

Answer 18

poor fusion s/p fracture
callus undergoes a cystic degeneration with synovial like cells

the body doesn’t view it as 2 pieces of the same bone. thinks it’s 2 separate bones and that there needs to be a joint there. puts synovial fluid in there like its a joint –> cystic degeneration