PSYCH M140 Chapter Notes - Chapter 2: Rheumatoid Arthritis, Maximum Life Span, Doubling Time
CONTROVERSY 2: WHY DO OUR BODIES GROW OLD?
Why Do Our Bodies
Grow Old?
• The maximum lifespan for the human species appears to be
around 120 years
o We have no valid records of people living much beyond
120 years
• Over recent years, life expectancy (e.g., average number of
years lived) has risen; but lifespan (e.g., maximum possible
length of life) hasn’t changed at all
• Compression of Morbidity theory—believes we should
aim for a healthy old age, followed by a rapid decline and
death, which would likely:
o Enhance the quality of life
o Extend life expectancy and “health span”
o Reduce health care costs and caregiver burden
The Process of
Biological Aging
• Normal Aging (Senescence)—an underlying time-
dependent biological process that, although not itself a
disease, involves functional loss and susceptibility to
disease and death.
o Gompertz Law—death rates for contemporary humans
double every 8 years (ex., a 38-year-old would be twice as
likely to die as a 30-year-old)
o Additionally, at any given age, men are twice as likely to die
as women
• Comparative Anatomy—the study of the structure of
different species
o Helps us understand differences in aging and lifespan
across species
o The rate of aging can be correlated with the amount of
time it takes the death rate of a species to double
§ e.g., the doubling time for humans is 8 years, but it is 10
days for a fruit fly and 3 months for a mouse
• Rate-of-Living Concept—the concept that metabolism and
life expectancy are closely related
o Smaller organisms, which have faster metabolisms, also
have shorter life expectancies
• Human beings have an average lifespan and maximum life
expectancy about twice as great as those of any other primate
Biological Theories of
Aging
• No single theory of aging explains all the complex
processes that occur in cells and body systems
o But ongoing research is finding new insights into why we
grow old
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• Two basic kinds of theory of aging:
o Chance—the result of external events
o Fate—the result of an internal necessity
• The question remains whether or not it’s possible to intervene
to correct damage to the aging body or modify the genetic
program
• Wear-and-Tear theory—sees aging as the result of chance
§ A good explanation for some aspects of aging, such as the
fact that our joints and bones become damaged over time
as an outcome of living
o Somatic Mutation theory—notes that cells can be damaged
by radiation, and as a result, mutate or experience genetic
changes
§ A more modern and sophisticated version of the wear-and
tear theory, but little science evidence to support it at this point
• Autoimmune theory—the system may eventually become
defective and no longer distinguish the body’s own tissues
from foreign tissues
o The body may then begin to attack itself, as suggested by
the increase with age in autoimmune diseases, such as
rheumatoid arthritis
• Aging-Clock theory—claims that aging is programmed into
our bodies like a clock ticking away from conception
• Cross-Linkage Theory—claims that the bodily changes that
we see as we age result from the accumulation of cross-
linking compounds in the collagen, which gradually
becomes stiff
o Collagen—a natural protein found in the skin, bones, and
tendons
• Free Radicals—damage created by free radicals
(molecules that appear as a byproduct of oxygen metabolism in
cells) eventually gives rise to the symptoms we recognize as
aging
o The body produces antioxidants — substances that
protect against free radicals that prevent damage to cells
• Cellular Theory—argues that aging ultimately results from
the progressive weakening of capacity for cell division,
perhaps through exhaustion of the genetic material
o Hayflick limit—the finite number of cell divisions that
normal human cells in tissue culture go through
§ Named after discoverer Leonard Hayflick (1961)
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Document Summary
Aging: the maximum lifespan for the human species appears to be around 120 years o we have no valid records of people living much beyond. Discuss hayflick"s basic premise regarding the increase in longevity of the human species. Important to provide it with more than the minimum required capacity in its vital organs. Physiological reserve of energy and functional capacity does not renew at the same rate that it incurs losses. _postpone until after reproductive maturity the effects of genes that perform wepll in youth but become mischief-makers later. Biogerontologists describe changes that occur as we age form the molecular level up to that of the whole animal. Assumption: longevity has increased due to biomedical breakthroughs. Fries and crapo, writing in the 1980s, provided a new syllogism about human aging. Perform basic research to understand the genetic, neurologic, or hormonal mechanisms that control the process, and then learn to modify them.
