27: Physiology Of Bone

Question 1

Function of organic components of bone

Answer 1

Contributes to flexibility and tensile strength of bone

Question 2

Seven organic components of bone

Answer 2

1. Collagen
2. Osteonectin
3. Osteocalcin
4. proteoglycans
5. sialoproteins
6. osteopontin
7. thrombospondin

Question 3

major organic component of bone

Answer 3

collagen

Question 4

osteonectin and osteocalcin: 2 functions

Answer 4

hydroxyapatite crystallization, Ca binding

Question 5

what do sialoproteins, osteopontin, and thrombospondin do?

Answer 5

mediate osteoclast adhesion to bone surface

Question 6

proteoglycan function

Answer 6

bind GFs

Question 7

two main inorganic bone components

Answer 7

hydroxyapatite, mineral salts (Calcium phosphate, calcium carbonate, K, Mg)

Question 8

osteocyte function

Answer 8

regulation of osteoblasts and osteoclasts by releasing paracrine factors

Question 9

Major stimulator and inhibitor of osteoclast differentiation

Answer 9

Stimulator: RANKL
Inhibitor: OPG

Question 10

TGF-B: two functions

Answer 10

1. Osteoblast stimulation

2. Increased OPG production

Question 11

BMP function

Answer 11

Potent osteoblast inducer

Question 12

rhBMP-2

Answer 12

Clinical use for fracture healing and spinal fusion

Question 13

RANKL function

Answer 13

Osteoclast activation

Question 14

Osteoprotegerin (OPG)

Answer 14

Mock receptor for RANKL -> prevents osteoclast activation

Question 15

FGFs (fibroblast GFs): two functions

Answer 15

1. Osteoblast proliferation

2. Enhance callus formation during fracture repair

Question 16

FGF-2

Answer 16

Stimulates angiogenesis during fracture repair

Question 17

IGFs (insulin-like GFs)

Answer 17

Increase bone collagen matrix synthesis

Question 18

What stimulates IGFs?

Answer 18

GH

Question 19

PDGF (platelet-derived GF)

Answer 19

Increases collagen synthesis

Question 20

Interleukins

Answer 20

Stimulate bone resorption

Question 21

IL-1

Answer 21

Most potent bone resorption stimulator

Question 22

What decreases IL-1 expression?

Answer 22

Estrogen

Question 23

What stimulates PTH production

Answer 23

Falling blood Ca levels

Question 24

Wolff’s Law

Answer 24

Bone reacts to mechanical cyclic stress by changing internal and external architecture to better withstand stress over a period of time

Question 25

Three reasons bones undergo constant remodeling

Answer 25

1. Repair microdamage 2. Maintain strength 3. Regulate serum Ca

Question 26

Three steps in bone remodeling process

Answer 26

1. Microdamage -> RANKL release 2. Osteoclast activation -> bone resorption 3. Reversal to bone formation, mineralization, and osteocytogenesis

Question 27

Primary vs secondary (direct vs indirect) fracture healing

Answer 27

Primary: requires no movement between fractured fragments Secondary: some movement between fragments present

Question 28

Does a callus form in primary fracture healing?

Answer 28

No

Question 29

Three possibilities for fracture healing based on amount of space between fragments

Answer 29

No space: lamellar bone forms 200-500nm space: woven bone -> lamellar bone 500+nm space: indirect healing occurs

Question 30

Five stages of indirect fracture healing

Answer 30

1. Hematoma 2. Week 1: Inflammatory phase 3. 2-3 weeks: soft callus forms 4. 4-12 weeks: hard callus forms 5. For years: remodeling of bone

Question 31

Three anti-resorption therapeutic agents

Answer 31

Bisphosphonates, estrogen, denosumab

Question 32

Bisphosphonates

Answer 32

Inhibit osteoclast activity

Question 33

Denosumab

Answer 33

mAb against RANKL

Question 34

PTH: continual vs intermittent (daily) administration (therapeutically)

Answer 34

Continual: stimulates osteoclast formation Intermittent: stimulates bone formation

Question 35

Estrogen

Answer 35

Decreases RANKL production -> fracture healing

Question 36

Thyroid hormones

Answer 36

Stimulate osteoclasts

Question 37

Glucocorticoids

Answer 37

Inhibit Ca absorption in gut -> increased PTH -> increased osteoclasts

Question 38

GH

Answer 38

Stimulates osteoblasts -> increase callus formation and fracture strength