Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Bone refilling in cortical bone multicellular units: Insights into
  tetracycline double labelling from a computational model   Bone remodelling is carried out by `bone multicellular units' (BMUs) in which
active osteoclasts and active osteoblasts are spatially and temporally coupled.
The refilling of new bone by osteoblasts towards the back of the BMU occurs at
a rate that depends both on the number of osteoblasts and on their secretory
activity. In cortical bone, a linear phenomenological relationship between
matrix apposition rate (MAR) and BMU cavity radius is found experimentally. How
this relationship emerges from the combination of complex, nonlinear
regulations of osteoblast number and secretory activity is unknown.
  Here, we extend our previous mathematical model of cell development within a
single BMU to investigate how osteoblast number and osteoblast secretory
activity vary along the BMU's closing cone. MARs predicted by the model are
compared with data from tetracycline double labelling experiments. We find that
the linear phenomenological relationship observed in these experiments between
MAR and BMU cavity radius holds for most of the refilling phase simulated by
our model, but not near the start and end of refilling. This suggests that at a
particular bone site undergoing remodelling, bone formation starts and ends
rapidly. Our model also suggests that part of the observed cross-sectional
variability in tetracycline data may be due to different bone sites being
refilled by BMUs at different stages of their lifetime. The different stages of
a BMU's lifetime depend on whether the cell populations within the BMU are
still developing or have reached a quasi-steady state while travelling through
bone. We find that due to their longer lifespan, active osteoblasts reach a
quasi-steady distribution more slowly than active osteoclasts. We suggest that
this fact may locally enlarge the Haversian canal diameter (due to a local lack
of osteoblasts compared to osteoclasts) near the BMU's point of origin.

14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
19
The categories of this paper are: eess
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The categories of this paper are: bayes-an
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
2
The categories of this paper are: math
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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph