Lecture 2 - Bone Flashcards
1
Q
Bone function
A
- support
- protection
- muscle attachment
- calcium store
- produce cells
- enable hearing
2
Q
Osteon structure
A
- Osteon = functional unit
- lamellae = concentric rings of bone tissue (layered)
- cement line = outer rings of bone tissue
- haversian canal = blood vessels run down centre (50-100um)
- lacunae = holes for osteocytes
- canaliculi - osteocyte communication
- Volkmann’s canal = perpendicular blood vessels
3
Q
Bone content
A
Organic = tensile strength, flexibility and durability
- Collagen I (90%)
- fibrous proteins
- GAGs
Mineral content = compressive strength
- hydroxyapatite
4
Q
Osteocytes
A
- within bone matrix
- communicate with canaliculi
- long-lived (several years)
- mechano-sensing
- maintenance: calcium homeostasis and microcrack detection
5
Q
Osteoblasts
A
- lay down bone (osteoid - type I collagen matrix) + apatite
- make collagen fibres and PGs
- can become osteocyte
6
Q
Osteoclasts
A
- remove bone: secrete H+ to dissolve mineral
- secrete collagenase to clear protein
- multinucleated
7
Q
Basic multicellular units (BMUs)
A
- bone lining cells (SC on endosteum)
- osteoclasts
- osteoblasts
8
Q
Bone turnover process
A
- damage
- bone lining cells recruit osteoclasts
- osteoclasts resorb bone
- osteoclast apoptosis
- osteoblasts fill pit with osteoid
- mineralisation of matrix
- maturation of matrix
9
Q
Absorbed energy on graph
A
area under stress-stain curve
10
Q
Factors affecting bone mechanical properties (4)
A
- Loading rate
- E increases with loading rate
- ductile-brittle transition
- bones adapted to absorb max energy
The faster bone is loaded, i.e., the higher the strain rate, the higher the Young’s modulus of the bone tissue. Therefore, bone becomes progressively stiffer and brittle with more strenuous activity. Bone is more likely to break if it is brittle. - Orientation
- collagen fibres aligned longitudinally
- stronger in compression
- stronger longitudinally
Bone is anisotropic, and its mechanical properties depend on the direction in which it is loaded. Bone has a higher ultimate strength in compression than in tension, and the ultimate strength is much less in shear. Long bone is stronger in the longitudinal direction than in the transverse direction. - Creep
- strain changes with constant load
- viscoelastic - depends on strain and history of strain - Age
- > Less stiffness
- > Less strong (UTS > by 2%/decade)
- >The mechanical properties of bone change with age. As bones age they become less stiff, less strong and more brittle, all of which combine to increase the risk of fracture.
11
Q
Wolff’s Law
A
Bone will adapt to the loads placed on it
12
Q
Measuring bone mineral content (BMC)
A
DEXA - dual energy xray absorptiometry
13
Q
Trabecular bone adaptation
A
direction of trabeculae align with principal stress
14
Q
Osteoporosis
A
- affects 50% > 75yrs
- £1.7 bn/yr to NHS
- decrease in BMD (<2.5 std dev below peak bone mass in healthy 20 yr)
- > increase in E (brittleness)
- disruption of trabecular structure
- weaker bone –> increase fracture risk
15
Q
Osteoporosis risks
A
- age: decrease estrogen and testosterone
- genetic
- diet: malnutrition - vit D deficiency
- inactivity
