Aging in Today's Environment (1987) / Chapter Skim
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3 Principles of Gerontology
3 Principles of Gerontology
Pages 28-45
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From page 28... ...
Maturation is usually defined as the achievement of sexual maturity and the adult stage of morphology and physiology. In addition, most gerontologists would not regard phenomena that were strictly coupled to chronologic time as fundamental, intrinsic aging processes.
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From page 29... ...
The aged population, however, is the primary focus of gerontology, and of this report, because it might be particularly vuinerable to many environmental agents as a result of normal age-related alterations in cellular structure and function, a general reduction in the ability to maintain physiologic homeostasis, and alterations acquired as a result of environmental exposures. Environmental agents conceivably act at any stage of the life cycle; precisely how they affect aging processes is not known, because the sum ject has not been adequately studied and because aging processes themselves have not been adequately described.
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From page 30... ...
Life span, however, is a constitutional feature of a species, and, although environmental agents can readily modulate the life expectancy of populations, in most instances the life span is not influenced. Indeed, because life span appears to be under polygenic control that involves several aging processes, one would not expect a single environmental intervention to have global effects on it.
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From page 31... ...
An agent that hastens the onset or increases the progression of a particular process or processes could be referred to as a "gerontogen.~ Such environmental agents would be expected to cause the premature onset or accelerated progress of functional decline and age-related disease, thus impairing the quality of life in the later decades. However, much more research on the fundamental mechanisms of aging will be needed before we can definitively evaluate potential environmental agents that influence aging processes.
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From page 32... ...
An example of the blurring of the deterministic and stochastic categorization is the use of terminal differentiation to explain the limited replicative life span of somatic cells (Bell et al., 1978; Martin et al., 1974) that is, populations of cells cease dividing because they have differentiated into more specialized ceils.
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From page 33... ...
Dete~i~iistic Theories Developmental Switches in Gene Expression Senescence does not appear to be programed in the same way as development that is, regulated by a series of linked gene actions, whose primary result is to produce a limited life span. Only under special conditions in organisms that have a single episode of reproduction in their lifetime (semelparous organisms)
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From page 34... ...
. The basis of the hypothesis is the finding in rats that basal plasma corticosterone concentrations increase with age, and that although the increase in plasma corticosterone in response to stress does not change with age, the return to basal concentrations after the removal of stress is markedly delayed with age.
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From page 35... ...
That could occur, for example, if the DNA polymerases of short-lived species were comparatively error-prone or if their various DNA repair mechanisms were comparatively inefficient. Support for the theory comes from observations of a positive correlation between species longevity and the efficiency of the cellular repair of DNA damage induced by ultraviolet light (Francis et al., 1981; Hart and SetIow, 1974~.
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From page 36... ...
Moreover, the theory predicts a predorn~nance of point mutations (missense and nonsense mutations) and an accumulation that exhibits exponential kinetics near the end of the natural life span.
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From page 37... ...
Recent work has shown, however, that food restriction can increase life span without decreasing the metabolic rate (McCarter et al., 1985~. It is conceivable, however, that dietary restriction could decrease the flux of active oxygen species independently of metabolic rate.
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From page 38... ...
He suggested that a loss of biologic function due to the nonenzymatic reaction of glucose with proteins and nucleic acids (the glycation of proteins and nucleic acids) , yielding advanced glycosylation end products, is a basic mechanism of aging.
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From page 39... ...
Thus, with age, serum thymic hormone activity declines, and the percentages of immature lymphocytes in the thymus gland and in the peripheral blood increase. Environmental agents with the potential to modulate those events early in life, either centrally (e.g., specific neurotoxins)
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From page 40... ...
The uses can be categorized as estimation of an individual's chronologic age, estimation of an individual's biologic or physiologic age, prediction of the occurrence of an age-associated disease, prediction of impending death, and prediction of the life span of a species. Each of these uses should be considered in regard to its relevance to aging.
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From page 41... ...
Increased arterial blood pressure is a risk factor for stroke (Kennel, 1985) , and the blood concentration ratio of total cholesterol or arterial low-density lipoprotein to high-density lipoprotein is a risk factor for coronary disease (Gotto, 1986~.
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From page 42... ...
Few manipulations are known to extend the life span (Sacher, 1977~. Low environmental temperature, food restriction, and genetic manipulations have that effect in poikilotherms, and food restriction has that effect in rodents, which are the only mammals in which lifespan extension by manipulation has been rigorously demonstrated.
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From page 43... ...
In addition, chronic illness often leads to other complications in the elderly, including thromboembolism, dehydration, urinary tract infection, pressure sores, hypostatic pneumonia, and immobility contractures. The elderly often manifest an altered response, both physical and psychologic, to disease.
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From page 44... ...
The several changes in human cutaneous anatomy and function now recognized to occur with age can increase the vuinerability of the elderly to both chemical and physical environmental insults. For example, altered barrier function of the stratum corneum (horny layer)
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From page 45... ...
is presumed to impair recognition of foreign antigens, possibly including malignantly transformed cells, in the skin. The well-documented loss of melanocytes (pigment celIs)
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