Investigations in this century have yielded a number of theories about the biological process of aging. None of them is entirely right or wrong, and they all provide clues to the mystery. It is difficult to define universal factors about mechanisms of aging. Humans do not all show the same changes at the same chronological age. Biological aging affects all body systems, but decline of function varies from organ to organ. Although the basic aging pattern in humans is the same everywhere, the rate of aging is affected by many factors, including genetics, the environment, and standards of living.
Genetic
Experiments on human cells in artificial cultures show that cells divide a limited number of times before they die. This suggests that every person inherits a program for his or her lifespan, called a “biological clock” or “genetic clock”.
Another genetic theory states that when the body is no longer able to reproduce cells, then decline of the body follows.
Errors in Protein Synthesis
Protein synthesis, or production, plays a major role in the growth and reproduction of body cells, and it is the chief process of repair. Cells that are destroyed daily are replaced and wounds heal. The “error theory” states that mistakes in protein synthesis can occur and will disorganize cell function. As these errors are passed on, they collect over a period of time and cause changes-called aging-in organs and tissues. Errors in protein synthesis within the cell can be random or they can be introduced by other factors, such as radiation.
Immunological Dysfunctions
Immunological Dysfunctions
The immune system protects the body from foreign proteins, such as bacteria and viruses, by secreting antibodies to destroy them. What happens if cells change with age-could they be treated as foreign protein? That is one possibility.
Another possibility is that, with age, these antibodies cannot always distinguish between normal and abnormal proteins; they sometimes attack normal cells and cause damage or aging. A third possibility is that the white blood cells, lymphocytes, that produce the antibodies become less efficient.
Cross-linking
Connective tissue is abundant throughout the body. This tissue provides the framework that supports other tissues. The proteins in these tissues bond with one another, cross-linking, as one grows older. This causes the loss of elasticity in body organs and structures along with dryness and sagging of the skin.
Free Radicals
A free radical is a highly reactive chemical that has an extra electron. Free radicals are produced inside the body in the course of normal living by the oxidation of fats, carbohydrates, and proteins, and when oxygen combines with other substances in the cell, such as environmental pollutants. The chemical reacts with and damages normal cells when it accumulates in body cells faster than it can be eliminated.
Other Biological Theories of Aging
Lipofuscin is a by-product of metabolism with no known function. With age, particles of this yellow-brown pigment accumulate in body organs and structures and may disrupt normal cell metabolism.
There may be a connection between decreased endocrine function and growing old, because some hormone preparations reverse signs of aging. Those who view the body as a complicated machine believe that injury and overuse will wear it out. The theory that stress causes aging is popular with some because stress has many adverse effects on the body, such as precipitating heart attacks.
Reference :
Farrell J : Nursing Care of the Older Person, J.B. Lippincott Company, Philadelphia, 1990.
