The Aging Process
The Aging Process
The Aging Process
Why should the human body give out after 70, 80, or even 120 years? Why are older people more susceptible to disease, more inclined to have impaired vision and hearing, and likely to lose some of the physical and mental capacity they once enjoyed?
There are no fully satisfactory answers to these questions. Although we are mortal, it is entirely possible that one day humans could live much longer. The present potential life span for humans is said to be 115 years and today thousands of people live to be over 100. United States citizens now expect to live an average of 74.7 years. Women have a life expectancy of 78.3 years and men 71.1 years. Yet these figures have very little to do with potential life expectancy, because most people have their life altered and cut short from disease and disability, not from aging.
No one is so old
as to think he cannot
live one more year.
-- Cicero (106-43 B.C.)
It is still true that approximately 70% of all deaths in the United States are from heart disease, strokes, and cancer. Other diseases, accidents, and violence account for the rest--but not age. These same diseases and Alzheimer's disease account for much of the disability attributed to aging. As these diseases are conquered, far more people will live to their full potential life span and remain active and healthy for life.
A lot is known about the diseases that affect people and cause death. Much less is known about real aging because it involves fundamental cell processes that are quite complex. However, this mystery of life is being unraveled and will offer opportunities in the future that were once considered to be only possible in science fiction. It is hard to improve on the advice given by Seneca (4 B.C. -65 A.D.) to eat moderate amounts of well-balanced foods, get plenty of fresh air, exercise, and live a stress-free life-style.
Your life literally depends upon the ability of your cells to regenerate. They do this in a manner similar to one-cell organisms that simply divide and go on living as two "daughter" one-cell organisms. Before your cells can divide to reproduce themselves, they must first produce a duplicate copy of the genes. One of the most important examples of replication is of your blood cells. Your red blood cells live only an average 110 days, and they must be constantly replaced. Without replacement, you would soon develop serious anemia. The lining of your small intestine is completely replaced every three days. Your skin is constantly regenerated with the new cells formed in the deeper layers, while the old cells move to the top and are shed. It is this constant state of regeneration that enables the body to be young. It also enables healing to take place, as occurs after an injury.
WHY DOESN'T THE BODY
TO RENEW ITSELF
INDEFINITELY SO THAT
WE DON'T GROW OLD?
There are a number of theories for this big question:
The regeneration process is under the control of a genetic script that determines when certain events should occur in your life. It controls when speech will begin, when teeth will erupt, the onset of puberty, the onset of menopause, and other changes in the stages of life. The nature of this script, sometimes called the biological clock, is not determined, but it is suspected that it is part of the brain's function.
Organs and tissues often undergo changes because the cells used to form them no longer function in the same manner that they once did when young, or in the first years of duplication. For example, ovaries are not activated until puberty arrives. What activates them? Then the ovaries begin to sputter to a stop. What stops ovarian function? The timing of these events depends on the genetic script a person inherits at birth.
Some investigators believe the immune system is responsible for aging. As people get older, two things happen related to this. The body produces more autoimmune antibodies. Sometimes these antibodies attack the body's own tissues as if they were foreign substances or bacteria. In extreme states they cause many diseases, called autoimmune diseases. Other changes occur when the body's immune defenses decrease. The thymus gland, which prepares white blood cells (the T-cells) to carry out their defense actions to protect the body, deteriorates. The decrease in immunity can cause a person to be more susceptible to diseases, like pneumonia, for example. In other words, the body just stops functioning, maybe because it accurately reads an unconscious signal from the brain that this person is discouraged and depressed and no longer wants to live.
There are other theories like the "free-radical theory" and the "cross-linked theory" that tells us what happens but does not tell us why. In fact, no theory really explains why the body ages.
A major concern of many people is the possibility that they will lose their mental abilities as they grow old. The extreme of this is senile dementia, which can result in a person being totally incapacitated and no longer in touch with reality. Medical science now recognizes that this is not aging at all, but the result of disease. The problem to solve here is not to unravel the mystery of aging, but to find ways of preventing and treating the diseases responsible for senile dementia. The complex interrelation of nerve cells and brain chemistry is one of the most important frontiers of medicine, and there is no doubt that within this field lie many of the answers to the questions about the biological clock that may determine the phases of life and aging.
THE AGING BRAIN
Often it is not aging but disuse that results in decreased mental functions with increasing age. Maintaining the ability to concentrate, continuing to stimulate your memory with memory tasks, and problem solving all help to maintain those functions. The brain may continue to regulate your blood pressure and heart rate and affect whether you sweat or not, because these functions are exercised, but if you don't use your brain for mental tasks, its ability to remember does decrease, not from age but from disuse.
Sexual interest does not disappear in women after menopause, but the loss of estrogen definitely influences a woman's interest in sex. Estrogen will maintain her organs in a state of sexual readiness. Estrogen replacement helps to prevent the loss of sexual interest and function.
The healthy older male continues to produce high levels of testosterone for life. The testicles clearly have a different age cycle from the ovaries. The failure of sexual performance in most older males is not related to lower testosterone levels. The failure to have an erection is usually related to poor circulation because of disease, changes in nerve fibers that control erection because of diabetes and other illness, or to medicines as used in the control of high blood pressure. The decrease in sexual activity in healthy older men seems to be related to opportunity and attitudes rather than hormone levels or real aging.
THE SENSE ORGANS
The special senses, such as hearing, seeing, and tasting, are extensions of the nervous system. The progressive loss of taste, smell, and hearing may represent aging of the end cells of the system, such as the taste bud cells or the cells in the nose to detect smell. You can compare them to the ovaries, which have a limited interval for normal function and then disappear. But these same end organ cells can also be affected by disease. The maintenance of these functions at optimal levels may depend on both preventing or curing disease and also preventing aging of specialized sensory cells.
Very little is known about aging of the heart. Coronary heart disease that results in heart attacks is not caused by aging at all. It is a disease of the arteries that supply the heart muscle. There are genetic factors that influence the level of cholesterol, which in turn may increase fatty-cholesterol blockage of coronary arteries. Many older people have a decreased capacity for physical activity because the heart has not been exercised adequately.
THE MUSCLES AND SKELETON
The changes in the muscles and skeleton are another area where disease is confused with age. A major portion of the decrease in muscle size and strength, seen as people get older, is from disuse. There is some loss of muscle fibers because some of the nerve cells in the spinal cord that control them degenerate with increasing age. But proper exercise can maintain, strengthen, and enlarge the remaining muscle fibers. The skeleton does begin to decrease in size after about age 30. The bones undergo constant changes with remodeling of the bone architecture. This is a regeneration process. After age 30, there is not as much new bone formed as is lost, resulting in a gradual decrease in skeletal size and strength.