Biomedical Engineering Reference
In-Depth Information
gans, and stem cell therapy to replace dead or dying cells. This approach is
like treading water in an ocean of aging processes, staving off the inevitable
for as long as possible. The third approach is age retardation. The strategy
is to learn about the underlying molecular causes for senescence and to de-
vise means for halting or greatly retarding them.
Theories of Aging and Approaches to Age Retardation
The field of aging research is very dynamic. Top-notch molecular biolo-
gists are in hot pursuit of the molecular and genetic bases for aging, and
some of them have even established biotech companies, hoping to capi-
talize on new discoveries that translate into age-retardation treatments.
some hypotheses for the cause of aging include preprogrammed cell death,
genes for aging, the accumulation of mutations in the DnA of body cells,
a buildup of cellular damage caused by
oxygen free radicals,
and hormonal
signals for aging. Whether human aging is due mainly to one of these or
a combination of factors is not yet known. Below, we delve a little deeper
into some of the proposed causes of aging and also look at some interven-
tions that have dramatic age-retardation effects in animals.
Are cells preprogrammed to die?
except for cancer cells and some stem cells,
most cells grow and divide for only what appears to be a preset number of
times. one theory of aging is that senescence and ultimate death are due
to cessation of cell divisions in vital organ systems. since cell regenera-
tion is essential to maintain tissues throughout a lifetime, organs become
weaker as division ceases in more and more cells. When dead cells are not
replaced, organs simply wear out and death follows.
Just what do biologists now know about the natural limits imposed upon
cell replication and the mechanism that enforces them? in 1961 leonard
hayflick and a coworker at the Wistar institute in Philadelphia showed that
somatic cells cultured under laboratory conditions undergo only a certain
number of cell divisions that seem preprogrammed according to animal
species and cell type (hayflick and moorhead 1961). hayflick worked pri-
marily with human skin cells called fibroblasts that normally inhabit the
spaces between tissues and produce components of connective tissue like
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