Thursday, September 15, 2005

INTRODUCTION

Dramatic differences in how people age raise questions about the biology of aging. Human life span can be extended only by identifying the basic processes of aging. Many factors, such as environment, preprogrammed genetics, cell depletion, organ exhaustion, and overall "wear and tear," rather than any single factor, seem to be involved.
All parts of the body are affected by aging. As the body ages the bones lose calcium. The bones become more brittle and heal more slowly. After age 60, degenerative arthritis often develops. The cartilage around the joints is often "worn" from years of use, and the lubricating fluid is often depleted. This makes for a slower-moving, stiffer person.
The brain shrinks as a person ages. Although the brain shrinks, intelligence doesn't seem to be affected. Most people maintain a high level of mental competence throughout life. A slight loss of memory usually occurs after age 50. The reflexes also become slower. Hearing losses usually begin around age 30. Men are more likely than women to encounter hearing losses. The first loss is usually among the high notes (above 15,000 hertz). Many older people also have trouble distinguishing between speech and background noise.
The lens of the eye steadily hardens over the years, often making it difficult for people over 40 to focus on near objects. Older eyes are also prone to cataracts and glaucoma. Pupils become smaller with age, allowing in less light and limiting night vision. As the body ages, it becomes flabbier. The amount of flab is determined by pinching the skin beneath the shoulder blade and measuring how thick it is. At age 20, the distance is usually 12 millimeters; at 30 it is about 14 millimeters. After 40 the distance remains about 16 millimeters.

As the body ages, the hair becomes thinner. At age 20, the diameter of a single hair is 101 microns. By age 70 the diameter has decreased to about 86 microns. Balding usually begins at the temples, producing a widow's peak that recedes with age. Next, the monk's spot, the circle on the back of the head, begins to lose hair. The two areas may eventually meet and leave a man bald. Although balding occurs mostly in men, women are also affected. Most women have thinning of the hair but very few actually become bald.
As the body ages, the heartbeat becomes weaker. The heart pumps less blood with each beat, so that the heart has to work harder to keep the body nourished. Indeed, cardiovascular disease is the leading cause of death among the elderly. As a person ages the muscles weaken, causing the back to slump. The disks between the bones of spine deteriorate and move closer together causing a loss of height. At age 30, about 70 pounds of a man's 175 pounds are muscle. Over the next 40 years a man will lose 10 pounds of that muscle. His shoulders narrow. The muscle becomes weaker and stiffer with age. A man's strength peaks at about 30 years of age and then steadily diminishes. In women, the decrease of muscle strength begins in the twenties. Fat gradually replaces muscle in the female body.
As the body ages, the nails grow more slowly. At age 20 a person's nails will grow 0.94 millimeters a week. At age 70 the nails grow only about 0.60 millimeters a week.

Reaction time slows with age. The reason for the slowdown of the reaction time is the increased time required by the brain to process information, make decisions, and dispatch signals.
The skin wrinkles automatically with age. The skin loses water and its molecules bind to each other, making for a stiffer, less elastic skin structure. The skin spreads out and thins, causing it to be "baggy" on the body.
Stamina decreases with age. The weakening of the heart, lungs, and muscles means that there is less oxygen coming in, and this oxygen is slower to disperse to the muscles. For instance, a healthy 70-year-old person can run a marathon, but it will take him or her at least an hour longer than it took at age 30.

A man's basal metabolism slows down by 3 percent each decade. Muscle and tissue die and are replaced by accumulated fat. At age 20 a man who weighs 165 pounds will be 15 percent fat. At age 70 this man will weigh about 178 pounds with 30 percent of his weight being fat. In women, the number of calories necessary to maintain a weight decreases by ten percent each decade after 20.

These body changes are an inevitable part of aging. They occur so gradually that most people do not recognize the changes.


SOURCES:
Krieger, L. "Why Do People Get Old." In Aging, Goldstein, E. c., ed. Vol. 3, Art. 18. Boca Raton, Fl.: Social Issues Resource Series, Inc., 1981.

Tierney, J. "The Aging Body." In Aging, Goldstein, E.C., ed. Vol. 2, Art. 24. Boca Raton, Fl.: Social Issues Resource Series, Inc., 1981.

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