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86 Cards in this Set

  • Front
  • Back
What is bone?
(3 things)
1. Anatomical organ (individual bones)
2. Physiological organ(metabolically active)
3. Composite material
Bone is a composite material: composed of . . .
(3 things)
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)
Functions of bone
•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
Functional demands that must be met by bone
•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
___________ fulfills physical material demands
Extra-cellular matrix
______ fulfill transport/growth/remodeling
Cells
Woven bone
Irregular collagen network

immature form & found in first stage of injury repair

relatively less mineralized than parallel-fibered bone
Parallel-fibered bone
Lamellar bone & primary osteonal bone
Osteoclasts=
= bone resorbing cells
Osteoblasts =
= bone matrix depositing cells
Osteocytes =
= “trapped” osteoblasts regulating calcium uptake/deposition, communicate with each other and osteoblasts through cannuliculae
Osteoid =
= collagen, bone matrix proteins, alkaline phosphatase
_______ collagen fibers are secreted by osteoblasts
Type I
Type I collagen fibers are secreted by osteoblasts ______ to ambient load orientation
parallel
__________ covers collagen surface
Hydroxyapatite
________ covers collagen surface
Hydroxyapatite
Hydroxyapatite Deposition starts where
in holes between ends of tropocollagens
Seed crystals of Hydroxyapatite initiate formation of larger needle-shaped crystals oriented __________
parallel to collagen
Collagen/carbon units surround the zones of matrix proteins in small amount of water T/F
T
Haversian system =
= osteon + blood vessels, the main circulatory supply
Primary osteon =
= first formed non-lamellar osteons
Secondary osteon =
= lamellar osteons resulting from remodeling
Periosteum =
= membrane on outer surface of bone
Cortical bone =
= dense bone with Haversian systems
Trabecular bone (cancellous) =
= buttresses arrayed along stress lines
Circumferential lamellar bone =
= outer layers of cortical bone lacking osteons
what type of vasculature is associated with marrow and endosteal surface
Emissary
What type of vasculature is associated with periosteal membrane
Periosteal
T/F there is a separation of supply to epiphysis in young bone
T
T/F cartilage is directly vascularized
F
Bone is plastic living tissue and responds to:
(4 things)
•Loading (tension, compression, shear)
•Vasculature (oxygen tension)
•Deformation by pressure
•Trauma
Default state of osteoclasts and osteoblasts is “ON”. T/F
T
T/F Remodeling is Continuous in normal adult; at any given time
T
in normal adult; at any given time ____% cortical bone & ____ % trabecular bone
3
7
“Life expectancy “ cortical bone: ____ yrs.
“Life expectancy” trabecular bone: ____ yrs
20
4
______ bone very rapid turnover; Primary Ca 2+ reservoir
Endosteal
________ ADAPTS THE CORTICAL THICKNESS, DIAMETER, CURVATURE AND ATTACHMENT SITE MORPHOLOGY TO HABITUAL FUNCTIONAL LOADS
REMODELING
During the Activation stage of remodeling activated __________ lining cells produce __________
osteoclast/ collagenase
collagenase digests _____ on bone surface, exposing mineralized matrix.
osteoid
Exposed bone matrix is chemotactic for _______ which are activated and migrate to exposed site
osteoclasts
Osteoclasts then do TWO things to desolve bone mineral before the organic matrix is phagocytized. What are they?
–form SEQUESTRUM
–secrete lysosomal enzymes, (acid phosphatase and proteolytic enzymes)
what is coupling
1-2 week gap between osteoclast resorbing & bone formation onset.
during Formation Osteoblasts line exposed bone surface Secrete _______.
osteoid
What is formation duration
about 3 months
When does Mineralisation commense
When is it complete
Commences 10-15 days after onset of formation. completion is 3-6 months after formation
Stimulators of remodeling
•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.
Summary of Remodeling Process
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.
Active growth is concentrated in ______/______ areas with intervening growth plate
metaphyseal/epiphyseal
Bone scans use a ______ to show site of epiphyseal growth activity (dark = actively growing)
tracer
_________ are still cartilaginous in babies
Epiphyses
_________ is translucent in radiographs
Growth plate
Near maturity, growth line at ______/______ junction is still visible
epiphyseal/metaphyseal
Resorption of existing bone is by ________
osteoclasts
RE: Shape change during growth, Bone responds to:
absence of loading by ______
loading by ________
resorption
proliferation
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
tubercles
pits
_______ growth studies are gold standard
Longitudinal
In longitudinal growth studeis there is a difference of __________ in peak velocity between sexes (males top, females bottom)
about 2 years
Developmental Age indicators in bone
•Proportion of secondary osteons

•Epiphyseal fusion state – variable with population and individual

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

•Dental development
Degenerative Age indicators in bone
•Pubic symphysis [Suchey stages III – VI]
•Sternal rib end
•Dental attrition
•Dental cementum annulation
•Osteoarthritis
Thickness varies with _____.
–Removal of weight can result in 60% loss of cortical mass from tibia and femur within a few weeks.
loading
Osteoclasts release __________ when mechanically stimulated
prostaglandins
Prostaglandins inhibit ___________
apoptosis of osteoblasts
Loss of mechanical stimulation = loss of _______ activity
osteoblastic
Vertebrae _______ to ______ in X-sectional area as you move caudally to compensate for increase in loading
smaller
larger
Bone material is weaker in _________ than in compression
tension/shear
Fractures common in areas of ______________
high tensile loading (e.g. avulsion at tendon/ligament insertions, tensile failure at femoral neck.)
Bending fractures can result in ________ pattern.
comminuted “butterfly”
Long axis of crystal/collagen/haversian arrays within ____ degrees of a long bone’s axis, usually much less.
45
Bone mechanics: When force is applied, material resists yet ______ to some degree
deforms
Three loading conditions:
• Tension
• Compression
• Sheer
loading conditions can combine in two ways
• Torsion and
• Bending.
• Stress =
load/area
• Strain =
deformation/original length
• Stiffness
stress/strain = load/deformation
Material characteristics of Collagen:
stiff and strong in tension, floppy in compression
Material characteristics of Apatite:
stiff in both compression and tension, but also weak in tension; susceptible to brittle fracture (fracture with virtually no plastic deformation)
put in order of greatest streagth:
compressive transverse
tensile transverse
compressive longitudinal
tensile longitudinal
compressive longitudinal
compressive transverse
tensile longitudinal
tensile transverse
Bone is less likely to undergo brittle fracture because ___________ interface blunts small cracks.
collagen/crystal
Bone is stronger and stiffer parallel to the crystal-collagen array; optimize mass relative to strength, trabeculae oriented ________ to ambient load.
parallel
T/F Strength equals stiffness
F--DOES NOT

Stiff & weak: chalk
Compliant & strong: hemp fibers
T/F Bone is weaker and more commonly fails in tension than compression
T
Onset of material failure =
yield point
strain @ yield for bone =
1%
Plastic deformation =
deformation beyond the yield point
Ultimate failure (fracture) point =
structural failure
strain @ fracture for bone =
= 2%