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Metaphysics
- Part of philosophy concerned with 'how do we age?'
- Seen as positive or negative event
- Positive: Robert Browning, fulfillment of life' journey
- Negative: Dylan Thomas, it's the END of all achievements
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Gerontology
- Branch of science asking the question 'what is aging?'
- Observational: Shakespeare's 7 ages of development & Aristotle's LOSS of heat with age theory
- Experimental: Metchnikoff and Raymond Pearl 1st to carryout aging experiments & Alex Comfort compiled data of aging of different organisms
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Ethics
- part of Philosophy concerned with 'should we interfere with aging process?'
- Hayflick: opposes attempts to INCREASE max lifespan
- Walford: in FAVOR of increasing max life
- Robert Arking (txtbook author): favors attempts to heal sick and increase lifespan but does not believe or desire human immortality
- Thomas: agrees with Walford in desire for immortality, although social upheal would result
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Bernard Strehler criteria for age-related changes leading to senescence
- 1. cumulative- increase over time
- 2. progressive - change in one direction, NOT in reverse
- 3. intrinsic - generated internally, not stopped by envir
- 4. deleterious - REDUCE fxn, lead to INCREASE in mortality rates over time
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Most widely used method to measure if aging is occurring in a population
Age-specific mortality rate
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Type I, II and III survivorship patterns on semi-log survivorship plot
- Type I (senescence): convex slope going downwards, showing INCREASE mortality with age
- Type II(nonsenescence): linear slope going down, constant mortality and life expectancy
- Type III(antisenescence): concave slope going down, showing DECREASED mortality and increased life expectancy with age
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Halley
made 1st human life table
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Weismann
- proposed DISPOSABLE SOMA theory of aging
- Theorized that somatic tissues always aging
- Germ cells, however, do NOT age
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Charles Child
- dissection with flatworms showed if cutting off head, able to regenerate infinite # of times
- if cut the tail, worm eventually dies
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Leonard Hayflick
human diploid fibroblasts have LIMIT to amount of cell divisions can occur in tissue culture (aka Hayflick limit)
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Why population data, although can suggest whether of not Type I aging is occurring, shows potential problems to predict patterns
- 1. pop. avgs can lose some info about INDIVIDUALS
- 2. Death rates altered by ENVIRON. changes
- 3. Death thresholds may Differ among indiv.
- 4. Accidental deaths may mask changes in age-related deaths
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To reduce problems with population data
- Longitudinal data: info on same indiv. @ multiple timepoints, vs. cross-sectional data (all members of pop @ one timepoint)
- Baltimore Longitudinal Study & Framingham Study: largest longitudinal studies in world
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Biomarkers of aging
Consistent changes in phyisiological parameters with age in diff. indiv.
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Bottoms up approach to study aging
free radical theory by Denham Harman: major success of this approach, by examining free radical
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Top-down approach to study aging
iron-accumulation hypothesis supports this approach, although can only divide pop so much before accidental deaths & other factors occur
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Problems to gerontology
- Longitudinal studies must take mortality rates into account, and hard for rodents who have longer lifespans, vs fruitflies for example
- protozoa do not have this problem
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Intraspecific plasticity
- Longevity can be influenced by ENVIRONMENTAL changes
- organisms with high reliability predictions with specific environments:
- 1. salmon - all die w/in same month after spawning upriver, from parasite infections
- 2. perennial plants - all die within same week in response to light & temp stimuli
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Interspecific plasticity
- a. Caleb Finch: wide range of aging patterns observed in nature classified into 3 groups:
- 1. Rapid
- 2. Gradual
- 3. Negligible senescence
- Problem is that it some species can be classified in more than 1 throughout their life (ie: bamboo, perennial plants)
- b. Raymond Pearl: classified based on Type I, II and III.
- Has advantage of NO ambiguity
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