Effects of aging on tissues
Describe the age-related changes that occur in cells and inextracellular matrix.
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 arteries.
However, it is increasingly evident that many of the cell losses and functional declines can be slowed by physical and mental exercises.