Theories of Aging
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The aging process may vary considerably both between individuals and among different species. Over the years, innumerable theories have been proposed in an attempt to explain this phenomenon. While none of these theories conclusively defines the physiological mechanisms of aging, many do seem plausible. Of the mammalian species, the human life span is greatest. In fact, in recent decades, entire populations of humans have been increasing in average age. This shift in age distributions has occurred primarily in the world's developed countries. Undoubtedly, such change will one day have implications for health care providers. In nursing, for example, a re evaluation of health care priorities could become necessary. The term, "senescence," can be defined as a "decline in the functional capacity of the body that occurs with age" (Mera, 1992, p. 271). Rates of aging are generally highly variable. Among mammals, life span ranges from a low of a few months to a high of 80 years or more (Charlesworth, 1003, p. 11). In addition, even within species, individuals of the same chronological age may show widely different senescence changes in various anatomic regions.Since the beginning of recorded history, many theories for aging have been proposed. For example, Hippocrates thought that old age was caused by an imbalance of the body's humors (e.g., blood, phlegm, and bile) with a gradual loss of body heat. Since the time of the Greeks, several additional a
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on of certain hormones. A decrease in the synthesis of various anabolic adrenocortical steroid hormones may be, at least in part, responsible for age-associated muscle wastage and osteoporosis. One particular hormone, dehydroepiandrosterone, may be directly involved in aging. In humans, levels of this compound peak around age 25 to 30, and decline thereafter. Among the hormone's many functions, the inhibition of certain carcinogenic substances could protect younger people from the diseases of old age. Lastly, the normal purpose of P glycoprotein is to remove toxins from within cells. Many believe that low levels of this compound results in aging. One problem with the enzyme-hormone-glycoprotein theory, however, is that the hypotheses lack definitive biochemical evidence. The "genetic time table" theory is the main biological clock theory. It states that "for each species, there exists a specific genetically determined maximum life span." Accordingly, pre determined physiologic changes occur in organisms which eventually result in aging and death. This theory does adequately describe the various differences in aging among the different species. For example, it is thought that large organisms with few young must
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Approximate Word count = 1562
Approximate Pages = 6 (250 words per page)
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