| Throughout history man has had to
accept the fact that all living things must die, but people now live longer than
they{{U}} (51) {{/U}}Yet, all living things still show the{{U}} (52)
of {{/U}}aging, which will eventually{{U}} (53)
{{/U}}death. Aging is not a disease, but as a person passes maturity, the cells of the body and the{{U}} (54) {{/U}}they form do not function{{U}} (55) {{/U}}they did in childhood and adolescence. The body provides less{{U}} (56) {{/U}}against disease mad is more{{U}} (57) {{/U}}accident. A number of related causes may{{U}} (58) {{/U}}aging. Some cells of the body have a fairly long life, but they are not{{U}} (59) {{/U}}when they, die. As a person ages,{{U}} (60) {{/U}}of brain cells and muscle cells decreases.{{U}} (61) {{/U}}body cells die and are replaced by new cells. In an aging person the{{U}} (62) {{/U}}cells may not be as viable or as{{U}} (63) {{/U}}growth as those of a young person. Another{{U}} (64) {{/U}}in aging may be changes within the cells{{U}} (65) {{/U}}Some of the protein chemicals in cells are known{{U}} (66) {{/U}}with age and become less elastic. This is why the skin of old people{{U}} (67) {{/U}}and hangs loose. This is also the reason old people{{U}} (68) {{/U}}in height. There may be other more important chemical changes in the cells. Some complex cell chemicals, such as DNA and RNA, store and{{U}} (69) {{/U}}information that the cells need. Aging may affect this{{U}} (70) {{/U}}and change the information-carrying molecules so that they do not transmit the information as well. |