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BBS2062 Case 2
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Case of 3 pages for the course BBS2062 Allometry at UM (BBS2062 Case 2)
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Case 2 Are mice big enough?Learning Goals:
What is the relationship between bone thickness and body mass? (Scaling book → chapter 5,
and reference 2 [Christen])
Bone remodelling
Bone thickness ->
Trabecular bone/spongy -> negatively with body mass
Smaller size -> higher metabolic rate (more cells, more activity, more remodelling)
Bones adapt to forces, loads and gravitation by altering shape, mass and microstructure. This
is done by trabecular bone modelling and remodelling. Osteocytes in bone senses
mechanical tissue loading and triggers osteoblasts and osteoclasts on the bone surface to
form and resorb bone.
Allometric relations
o Trabecular bone microstructural parameters, including trabecular thickness, spacing,
and number, scale with animal size with negative allometry.
o Trabecular length and diameter scale with animal size with negative allometry
o Osteocyte density is inversely related to animal size, possibly adapted to metabolic
rate, which shows a negative relationship as well.
- Smaller animals higher BMR bone remodelling has a higher turnover
speed in smaller animals
- In addition, the signalling reach of osteocytes is limited by the extent of
the lacuno‐canalicular network, depending on trabecular dimensions and
thus also on animal size.
o Bone volume fraction (BV/TV, bone volume to total volume) and degree of
anisotropy are independent of body mass.
What is the relationship between cartilage and body mass? (reference 6)
o Cartilage thickness scales according to negative allometry, and, as a result, cartilage
is relatively thinner in larger animals.
- Because cartilage is avascular, it has a limited thickness, otherwise a
number of cells wouldn’t get nutrients/oxygen
Ratios within cartilage do not change much between body size
Reptiles have more cartilage
As trabecular length measures change with the cubic body mass to the 1/3 power, every
scaling exponent below 1/3 is regarded as negative allometry.
Therefore, negative allometry of trabecular bone scaling means that smaller animals show
relatively thicker, more separated, and fewer trabeculae than expected from geometric
similarity
- Bone length ∞ M1/4
- Bone diameter ∞ M3/8
Wolff’s law describes the response of bone to mechanical loading and bone functional
adaption.
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