Physiology of Bone

Question 1

What is mainly found in the organic portion of the ECM in bone?

Answer 1

collagen

Question 2

What organic component in the ECM of bone aids in hydroxyl apatite crystallization and binds calcium?

Answer 2

Osteonectin and osteocalcin

Question 3

What organic components of the ECM of bone binds growth factors?

Answer 3

Proteoglycans

Question 4

What organic components of the ECM in bone mediate osteoclast adhesion to bone surface (bind osteoclast integrins)

Answer 4

Sialoproteins, osteopontins, and thrombospondin

Question 5

What are the main inorganic components of the ECM of bone?

Answer 5

inorganic hydroxyapatites or mineral salts, primarily calcium phosphate

Question 6

What functions to pack tightly, contributing to the hardness and ability to resist compression?

Answer 6

the inorganic components

Question 7

What is the function of osteogenic cells?

Answer 7

develop into osteoblasts

Question 8

Where are osteogenic cells located?

Answer 8

in the deep layers of the periosteum and the marrow

Question 9

What is the function of osteoblasts?

Answer 9

Bone formation

Question 10

Where are osteoblasts found?

Answer 10

in growing portions of bone, including periosteum and endosteum

Question 11

what is the function of osteocytes

Answer 11

maintain mineral concentration of matrix

Question 12

where are osteocytes found?

Answer 12

entrapped in matrix

Question 13

what is the function of osteoclasts?

Answer 13

bone resorption

Question 14

where are osteoclasts found?

Answer 14

bone surfaces and site of old or injured bone matrix

Question 15

Which bone cell type is cuboidal shaped?

Answer 15

osteoblast

Question 16

which bone cell type directly regulates bone matrix synthesis and mineralization?

Answer 16

osteoblasts

Question 17

How doe osteoblasts indirectly control bone resorption?

Answer 17

Through release of paracrine factors that regulate osteoclasts (RANKL/OPG)

Question 18

What do osteoblasts eventually become?

Answer 18

osteocytes

Question 19

Which bone cell can initiate apoptosis?

Answer 19

Osteoblasts

Question 20

Which bone cell type is the terminally differentiated osteoblast?

Answer 20

Osteocytes

Question 21

Where do osteocytes become trapped?

Answer 21

Within the newly deposited bone matrix

Question 22

How do osteocytes respond to mechanical loading?

Answer 22

by releasing paracrine factors

Question 23

Which bone cell secretes acid and lytic enzymes?

Answer 23

Osteoclasts

Question 24

Which bone cells are multinucleated and are derived from mononuclear cells in the bone marrow?

Answer 24

Osteoclasts

Question 25

What stimulates the proliferation and differentiation of osteoblasts and bone formation?

Answer 25

TGF-B

Question 26

What increases OPG production?

Answer 26

TGF-B

Question 27

What is a potent inducer of osteoblasts and bone formation?

Answer 27

Bone Morphogenic Proteins (BMPs)

Question 28

How is BMP used clinically?

Answer 28

rhBMP-2 is used in fracture healing and spinal fusions

Question 29

What is secreted by osteoblasts, binds RANKL, and prevents osteoclast activation?

Answer 29

Osteoprotegerin (OPG)

Question 30

What increases proliferation of osteoblasts and enhances callus formation during fracture repair?

Answer 30

Fibroblast Growth Factors (FGFs)

Question 31

What does FGF-2 stimulate?

Answer 31

Angiogenesis during fracture repair

Question 32

What is stimulated by growth hormone and increases bone collagen matrix synthesis and inhibits degradation?

Answer 32

Insulin-like growth factors (IGFs)

Question 33

What increases collagen synthesis?

Answer 33

Platelet Derived growth factor (PDGF)

Question 34

What activates osteoclasts for bone resorption?

Answer 34

RANKL

Question 35

What secretes RANKL?

Answer 35

osteoblasts

Question 36

What is RANKL regulated by?

Answer 36

OPG

Question 37

What stimulates bone resorption and which is the most potent?

Answer 37

Interleukins; IL-1 is the most potent

Question 38

What is IL-1 expression decreased by?

Answer 38

Estrogen

Question 39

What signals release of PTH?

Answer 39

Falling blood calcium levels (hypocalcemia)

Question 40

What does PTH signal?

Answer 40

Signals osteoclasts to degrade bone matrix and release Ca into the blood

Question 41

Limited movement would result in which type of fracture healing?

Answer 41

indirect bone healing

Question 42

No movement would result in which type of fracture healing?

Answer 42

direct bone healing

Question 43

When is the inflammatory phase of indirect (secondary) fracture healing?

Answer 43

~1 week

Question 44

When is the soft callus formation in indirect (secondary) fracture healing?

Answer 44

weeks 2-3

Question 45

When is the hard callus formation in indirect (secondary) fracture healing?

Answer 45

weeks 4-12

Question 46

When does remodeling of bone occur in indirect (secondary) fracture healing?

Answer 46

years

Question 47

If there is direct contact between fragment ends, what forms?

Answer 47

lamellar bone

Question 48

If there is a gap of 200-500 nm, what forms?

Answer 48

woven bone and then eventually lamellar bone

Question 49

If there is a gap of 500 nm what occurs?

Answer 49

Indirect healing

Question 50

What inhibits osteoclast activity and induces osteoclast apoptosis?

Answer 50

bisphosphonates

Question 51

What is a monoclonal antibody against RANKL?

Answer 51

Denosumab

Question 52

What induces osteoblast proliferation and activity for increased bone matrix production?

Answer 52

BMP-2

Question 53

What effect do thyroid hormones have on bone metabolism?

Answer 53

They (thyroxine and triiodothyronine) stimulate osteoclastic bone resorption

Question 54

What effect do glucocorticoids have on bone metabolism?

Answer 54

they inhibit calcium absorption from gut, which causes increased PTH and therefore increased orthoclastic bone resorption

Question 55

What does intermittent exposure to PTH stimulate?

Answer 55

osteoblasts and increased bone formation

Question 56

What does more chronic exposure of pathological levels of PTH stimulate?

Answer 56

osteoclasts to release calcium, which can lean to hypercalcemia

Question 57

What effect does growth hormone have on bone metabolism?

Answer 57

It increases callus formation and fracture strength by stimulating osteoblasts