You Are At: AllSands Home > Science > How the body changes with age
The human body will go through many noticeable changes with age. In the United States the average life expectancy has increased dramatically over the years and yet the oldest age to which people can live has changed little since the 1900's. In spite of an excellent genetic make up and the best of medical care, the life expectancy will very seldom go beyond 120 years of age. It is a known fact that every species known to man goes through changes from the time of birth until death. Scientists have studied the aging process for years and though there are many theories, none have been proven.

One theory, the programmed senescence theory, shows that the rate a which a species ages is predetermined by its genes. Since genes determine the length of time a cell lives, this theory states that as cells die the organs begin to malfunction. This leads eventually to the inability of these organs to maintain the biological functions that are necessary to sustain life. This theory shows that due to this sequence the preservation of a species is maintained as older members die at a rate that allows room for the younger of the species. Another theory, the free radical theory, states that cells age as a direct result of accumulated harm from continued chemical reactions within the cells. According to this theory toxins called free radicals are produced and ultimately damage the cells, causing a person to age. As the person ages, more and more damage is done until enough cells have died to cause other cells to be unable to function normally. Thus the body dies. This theory also states that different species age at different rates depending on the production of cells and how they respond to free radicals.

In most humans the first noticeable sign of aging occurs when the eye cannot focus on close objects. This is called presbyopia and often by around age 40 people begin to find it difficult to read without glasses. In many cases a person will also tend to lose some of their ability to hear the highest pitched tones. Such sounds as k, t, s, p and ch begin to fade, causing an older person to think others are mumbling. The proportion of body fat increases by more than 30 percent with age and the distribution begins to change. Less fat forms under the skin and more accumulates in the abdominal area. Thus the skin becomes thinner and begins to wrinkle. As a person ages the skin will become more fragile and the shape of their torso will change.

But appearance and senses are not the only things that change with age. The internal functions begin to decline after they have peaked at around age 30. As the body ages the blood flow to the kidneys, brain and liver decreases. There is a decrease in the kidneys' ability to clear toxins and drugs. The liver's ability to metabolize most drugs and clear toxins begins to decline as well. The maximum heart rate decreases, although the resting heart rate does not change. The maximum output of blood from the heart decreases, as does the glucose tolerance. In the lungs the air moving capacity decreases and the amount of air trapped in the lungs after exhaling increases. The infection fighting function of the cells will also begin a slow decline. Even so, these functions will still remain adequate throughout the remainder of a persons life. If a person gets plenty of exercise, eats a good diet and does not smoke or drink, chances are they will not experience these adverse effects as quickly as a person whose life style is less healthy.