Reorganisation and Restoration of Bone
Changes in the size and shape of
bones during the period of growth imply some bone reorganisation. Osteoblast
and osteoclast constantly deposit and remove bone to adjust its properties to
growth-related demands on size and/or changes of tensile and compressive
forces.Although the reorganisation of bone may not result in macroscopically
visible changes of bone structure, it continues throughout life to mend damage
to bone (e.g. microfractures) and to counteract the wear and tear occurring in
bone. Osteoclasts and osteoblasts remain the key players in this process.
Osteoclasts "drill" more or less circular tunnels within existing
bone matrix.
Osteoblasts deposit new lamellae of bone matrix on the walls of these
tunnels resulting in the formation of a new Haversian system within the matrix
of compact bone. Parts of older Haversian systems, which may remain between the
new ones, represent the interstitial lamellae in mature bone. Capillaries and
nerves sprout into new Haversian canals. Restorative activity continues in aged
humans (about 2% of the Haversian systems seen in an 84 year old individual
contained lamellae that had been formed within 2 weeks prior to death!).
However, the Haversian systems tend to be smaller in older individuals and the
canals are larger because of slower bone deposition. If these age-related
changes in the appearance of the Haversian systems are pronounced they are
termed osteopenia or senile
osteoporosis. The reduced strength of bone affected by osteoporosis will
increase the likelihood of fractures.
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Title:
Reorganisation and Restoration of Bone
by:
om
at
2013-02-15T03:05:00+07:00
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Reorganisation and Restoration of Bone