The biological mechanisms of ageing are poorly
understood. One of the few areas in which reasonable
progress is being made is in the age-related changes
in connective tissues. This is understandable since
connective tissues are involved in many of the gross
manifestations of ageing such as wrinkling of the
skin, physical disabilities of joints, and vascular
disease. Even here, however, we are only beginning
to learn of the nature of the age changes in precise
biochemical and biophysical terms. Only recently has
our knowledge of the connective tissue components
collagen, proteoglycans, and elastin progressed to the
point where we can frame sound questions about
their changes with age.
It is important to attempt to define ageing since
many studies, supposedly describing age changes,
deal with changes that are more reasonably regarded
as being due to growth and maturation. There is no
consensus on which definition should be adopted
but Strehler (1962) has suggested criteria which any
change must meet if it is to be regarded as a true
ageing event. True ageing changes should be
(1) universal-that is, they must occur in all members
of the population; (2) intrinsic to the organismthat
is, a change must not be a function of diet,
disease, environment, or other external influences;
(3) progressive; and (4) deleterious to the organism.
While the applicability of such criteria can be
questioned they nevertheless provide a framework
for assessing whether changes are true age changes.
In certain instances, particularly at a molecular
level, it is difficult to determine whether changes
might be deleterious. This is because their implications
in terms of the function of a tissue or an
organ are not always clear.
Another problem in studies of ageing is to
differentiate between chronological and physiological
age. This is particularly difficult in randomly
bred (human) populations where individuals vary
widely in their physiological capabilities at any
particular chronological age. This may be less of a