aging on tissues
Describe the age-related changes that occur in cells and inextracellular
The consequences of some age-related changes are obvious, whereas
others are subtle. For example, the appearance of skin changes as people age,
and athletic performance declines, after approximately 30 to 35 years. With
advanced age, the number of neurons and muscle cells decreases substantially.
Reduced visual acuity, smell, taste, and touch occur, and the functional
capacities of the respiratory and cardiovascular systems decline.
At the tissue level,
age-related changes affect cells and the extracellular matrix produced by them.
In general, cells divide more slowly in older than in younger people. The rate
of red blood cell synthesis declines in the elderly. Injuries in the very young
heal more rapidly and more completely than in older people, in part, because of
the more rapid cell division. For example, a frac-ture in an infant’s femur is
likely to heal quickly and eventually leave no evidence in the bone. A similar
fracture in an adult heals more slowly, and a scar, seen in radiographs of the
bone, is likely to persist throughout life.
The consequences of changes in the
extracellular matrix are important. Collagen fibers become more irregular in
structure, even though they may increase in number. As a consequence,
\connective tissues with abundant collagen, such as tendons and ligaments,become
less flexible and more fragile. Elastic fibers fragment, bind to Ca2+,
and become less elastic, causing elastic connective tissues to become less
elastic. The reduced flexibility and elasticity of con-nective tissue is
responsible for increased wrinkling of the skin, as well as an increased
tendency for older people’s bones to break.
The walls of arteries become
less elastic because of changes in collagen and elastic fibers. Atherosclerosis
results as plaques form in the walls of blood vessels, which contain collagen
fibers, lipids, and calcium deposits. These changes result in reduced blood
supply to tissues and increased susceptibility to blockage and rupture of
However, it is increasingly
evident that many of the cell losses and functional declines can be slowed by
physical and mental exercises.