Bone Growth Remodeling

Front 1

What is bone?
(3 things)

Back 1

1. Anatomical organ (individual bones)
2. Physiological organ(metabolically active)
3. Composite material

Front 2

Bone is a composite material: composed of . . .
(3 things)

Back 2

1. cells
2. surrounded by organic collagen extra-cellular matrix
3. imbedded with crystalline mineral (calcium phosphate – hydroxyapatite, with mixtures of other salts, including strontium, barium, carbonate)

Front 3

Functions of bone

Back 3

•Provision of rigid lever arms for movement & support
•Protection of vital soft tissue
•Readily-accessible mineral reservoir (calcium and phosphorus)
•Space for hemopoesis\immune cell generation

Front 4

Functional demands that must be met by bone

Back 4

•Resist compressive, tensile, shear, bending and torsional forces
•Be stiff but not overly brittle
•Accommodate growth
•Adapt to local physical demands throughout ontogeny
•Repair
•Act as calcium reservoir

Front 5

___________ fulfills physical material demands

Back 5

Extra-cellular matrix

Front 6

______ fulfill transport/growth/remodeling

Back 6

Cells

Front 7

Woven bone

Back 7

Irregular collagen network

immature form & found in first stage of injury repair

relatively less mineralized than parallel-fibered bone

Front 8

Parallel-fibered bone

Back 8

Lamellar bone & primary osteonal bone

Front 9

Osteoclasts=

Back 9

= bone resorbing cells

Front 10

Osteoblasts =

Back 10

= bone matrix depositing cells

Front 11

Osteocytes =

Back 11

= “trapped” osteoblasts regulating calcium uptake/deposition, communicate with each other and osteoblasts through cannuliculae

Front 12

Osteoid =

Back 12

= collagen, bone matrix proteins, alkaline phosphatase

Front 13

_______ collagen fibers are secreted by osteoblasts

Back 13

Type I

Front 14

Type I collagen fibers are secreted by osteoblasts ______ to ambient load orientation

Back 14

parallel

Front 15

__________ covers collagen surface

Back 15

Hydroxyapatite

Front 16

________ covers collagen surface

Back 16

Hydroxyapatite

Front 17

Hydroxyapatite Deposition starts where

Back 17

in holes between ends of tropocollagens

Front 18

Seed crystals of Hydroxyapatite initiate formation of larger needle-shaped crystals oriented __________

Back 18

parallel to collagen

Front 19

Collagen/carbon units surround the zones of matrix proteins in small amount of water T/F

Back 19

T

Front 20

Haversian system =

Back 20

= osteon + blood vessels, the main circulatory supply

Front 21

Primary osteon =

Back 21

= first formed non-lamellar osteons

Front 22

Secondary osteon =

Back 22

= lamellar osteons resulting from remodeling

Front 23

Periosteum =

Back 23

= membrane on outer surface of bone

Front 24

Cortical bone =

Back 24

= dense bone with Haversian systems

Front 25

Trabecular bone (cancellous) =

Back 25

= buttresses arrayed along stress lines

Front 26

Circumferential lamellar bone =

Back 26

= outer layers of cortical bone lacking osteons

Front 27

what type of vasculature is associated with marrow and endosteal surface

Back 27

Emissary

Front 28

What type of vasculature is associated with periosteal membrane

Back 28

Periosteal

Front 29

T/F there is a separation of supply to epiphysis in young bone

Back 29

T

Front 30

T/F cartilage is directly vascularized

Back 30

F

Front 31

Bone is plastic living tissue and responds to:
(4 things)

Back 31

•Loading (tension, compression, shear)
•Vasculature (oxygen tension)
•Deformation by pressure
•Trauma

Front 32

Default state of osteoclasts and osteoblasts is “ON”. T/F

Back 32

T

Front 33

T/F Remodeling is Continuous in normal adult; at any given time

Back 33

T

Front 34

in normal adult; at any given time ____% cortical bone & ____ % trabecular bone

Back 34

3
7

Front 35

“Life expectancy “ cortical bone: ____ yrs.
“Life expectancy” trabecular bone: ____ yrs

Back 35

20
4

Front 36

______ bone very rapid turnover; Primary Ca 2+ reservoir

Back 36

Endosteal

Front 37

________ ADAPTS THE CORTICAL THICKNESS, DIAMETER, CURVATURE AND ATTACHMENT SITE MORPHOLOGY TO HABITUAL FUNCTIONAL LOADS

Back 37

REMODELING

Front 38

During the Activation stage of remodeling activated __________ lining cells produce __________

Back 38

osteoclast/ collagenase

Front 39

collagenase digests _____ on bone surface, exposing mineralized matrix.

Back 39

osteoid

Front 40

Exposed bone matrix is chemotactic for _______ which are activated and migrate to exposed site

Back 40

osteoclasts

Front 41

Osteoclasts then do TWO things to desolve bone mineral before the organic matrix is phagocytized. What are they?

Back 41

–form SEQUESTRUM
–secrete lysosomal enzymes, (acid phosphatase and proteolytic enzymes)

Front 42

what is coupling

Back 42

1-2 week gap between osteoclast resorbing & bone formation onset.

Front 43

during Formation Osteoblasts line exposed bone surface Secrete _______.

Back 43

osteoid

Front 44

What is formation duration

Back 44

about 3 months

Front 45

When does Mineralisation commense
When is it complete

Back 45

Commences 10-15 days after onset of formation. completion is 3-6 months after formation

Front 46

Stimulators of remodeling

Back 46

•Systemic hormones (vitD, PTH)
•Local factors (cytokines, TGF-B, bone morphogenetic proteins BMP 1-7)
•Mechanical loading (4 cycles/day of weight-bearing strain sufficient to maintain bone mass.

***Experimental evidence suggests that remodeling driven by largest strain, even if infrequent.

Front 47

Summary of Remodeling Process

Back 47

Osteoclasts advance in wave to form “cutting cone”, dissolving and phagocytizing bone.

Osteoblasts follow along newly-created surface, secreting osteoid (matrix).

The osteoid is mineralized, trapping osteocytes in lacunae.

Front 48

Active growth is concentrated in ______/______ areas with intervening growth plate

Back 48

metaphyseal/epiphyseal

Front 49

Bone scans use a ______ to show site of epiphyseal growth activity (dark = actively growing)

Back 49

tracer

Front 50

_________ are still cartilaginous in babies

Back 50

Epiphyses

Front 51

_________ is translucent in radiographs

Back 51

Growth plate

Front 52

Near maturity, growth line at ______/______ junction is still visible

Back 52

epiphyseal/metaphyseal

Front 53

Resorption of existing bone is by ________

Back 53

osteoclasts

Front 54

RE: Shape change during growth, Bone responds to:
absence of loading by ______
loading by ________

Back 54

resorption
proliferation

Front 55

Bone responds to tension with either osteolytic or osteoproliferative response
-Same bones can produce different response
-Both _________ and _____ produce net increase in fibre attachment area

Back 55

tubercles
pits

Front 56

_______ growth studies are gold standard

Back 56

Longitudinal

Front 57

In longitudinal growth studeis there is a difference of __________ in peak velocity between sexes (males top, females bottom)

Back 57

about 2 years

Front 58

Developmental Age indicators in bone

Back 58

•Proportion of secondary osteons

•Epiphyseal fusion state – variable with population and individual

•Pubic symphysis “epiphyseal” fusion [Suchey stages I – II]

•Dental development

Front 59

Degenerative Age indicators in bone

Back 59

•Pubic symphysis [Suchey stages III – VI]
•Sternal rib end
•Dental attrition
•Dental cementum annulation
•Osteoarthritis

Front 60

Thickness varies with _____.
–Removal of weight can result in 60% loss of cortical mass from tibia and femur within a few weeks.

Back 60

loading

Front 61

Osteoclasts release __________ when mechanically stimulated

Back 61

prostaglandins

Front 62

Prostaglandins inhibit ___________

Back 62

apoptosis of osteoblasts

Front 63

Loss of mechanical stimulation = loss of _______ activity

Back 63

osteoblastic

Front 64

Vertebrae _______ to ______ in X-sectional area as you move caudally to compensate for increase in loading

Back 64

smaller
larger

Front 65

Bone material is weaker in _________ than in compression

Back 65

tension/shear

Front 66

Fractures common in areas of ______________

Back 66

high tensile loading (e.g. avulsion at tendon/ligament insertions, tensile failure at femoral neck.)

Front 67

Bending fractures can result in ________ pattern.

Back 67

comminuted “butterfly”

Front 68

Long axis of crystal/collagen/haversian arrays within ____ degrees of a long bone’s axis, usually much less.

Back 68

45

Front 69

Bone mechanics: When force is applied, material resists yet ______ to some degree

Back 69

deforms

Front 70

Three loading conditions:

Back 70

• Tension
• Compression
• Sheer

Front 71

loading conditions can combine in two ways

Back 71

• Torsion and
• Bending.

Front 72

• Stress =

Back 72

load/area

Front 73

• Strain =

Back 73

deformation/original length

Front 74

• Stiffness

Back 74

stress/strain = load/deformation

Front 75

Material characteristics of Collagen:

Back 75

stiff and strong in tension, floppy in compression

Front 76

Material characteristics of Apatite:

Back 76

stiff in both compression and tension, but also weak in tension; susceptible to brittle fracture (fracture with virtually no plastic deformation)

Front 77

put in order of greatest streagth:
compressive transverse
tensile transverse
compressive longitudinal
tensile longitudinal

Back 77

compressive longitudinal
compressive transverse
tensile longitudinal
tensile transverse

Front 78

Bone is less likely to undergo brittle fracture because ___________ interface blunts small cracks.

Back 78

collagen/crystal

Front 79

Bone is stronger and stiffer parallel to the crystal-collagen array; optimize mass relative to strength, trabeculae oriented ________ to ambient load.

Back 79

parallel

Front 80

T/F Strength equals stiffness

Back 80

F--DOES NOT

Stiff & weak: chalk
Compliant & strong: hemp fibers

Front 81

T/F Bone is weaker and more commonly fails in tension than compression

Back 81

T

Front 82

Onset of material failure =

Back 82

yield point

Front 83

strain @ yield for bone =

Back 83

1%

Front 84

Plastic deformation =

Back 84

deformation beyond the yield point

Front 85

Ultimate failure (fracture) point =

Back 85

structural failure

Front 86

strain @ fracture for bone =

Back 86

= 2%