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Lecture 6 -Theories of Aging.
A&G: Chapter 3- Theories of Aging: Biological and Psychosocial Theories.
The Canada Health Act
The Canada Health Act is federal legislation that was adopted in 1984 that specifies the conditions in which
provincial and territorial health insurance programs must operate in order to receive federal transfer payments
under the Canada Health Transfer. These conditions include: Public administration, Comprehensiveness,
Universality, Portability, and Accessibility (Health Canada, 2010). The provincial and territorial governments
are in turn, responsible for managing and delivering their health care services (Health Canada, 2010).
Models and Theories :
- Models and theories are often times not carefully distinguished from one another in the literature and
create this ongoing problem.
- Aging is usually defined as the: biological impairment of normal function, probably as a result of
changes made o cells and structural components. Death is the final event. is defined as the gradual biological
impairment of normal function, probably as a result of changes made to cells
Theories of Aging:
- Aging processes occur at the biological, psychological and social levels.
-Bengtson, Rice and Johnson (1999) argued that there were 2 reasons why there was a lack of combined
integration in gerontology.
1) 3 different aspects of age on which theories can focus.
a) Characteristics of the aging population
b) The developmental or aging process
c) The way in which age is incorporated into the social structure
2) In gerontology it starts from facts (systematic observation) that may be grouped loosely into models
and only rarely achieve the status of theory
Gender is one of the strongest predictors of life expectancy with women living longer than men.
Most t are Models not theories
Rowe and Kahn’s (1998) theory of successful aging (good physical and mental health, and social functioning)
Ford and Lerner’s (1992) developmental systems theory are not really theories.
Kyuper and Bengston= social breakdown theory argues physical, psychological and social health are
tightly linked in later life and problems in one area may cause problems in another area
Campisise= possible link between caloric restriction and altered gene expression
Von Dras and Blumenthal = psychological factors moderate the rate of aging and there are no genetic
programs that specifies senescence- only maximum lifespan
Walker, et al = trade off between alleles that confer extended life span versus those that confer
adaptational fitness.
Maruyama (1963) = Deviation Amplification Model
- classic systems theory model- homeostasis – by Bertalanffy (1969) and theory that after a system is jarred out
of homeostasis, the deviation mechanisms take over to accelerate works together and is a better theory of aging
than the one below
Goldberger (1996), Chaos theory= initially small changes can result in very large differences between
systems or individuals.
Aldwin and Stokols (1988) used Maruyama’s model to describe the effects of environmental stress.
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Biological Processes relevant to aging
1) those that promote homeostasis and decelerate aging
2) those that amplify the aging processes
Biological Theories of Aging
-only looks at the one that supports the deviation amplification theory
-loosely group into genetic, molecular/cellular, and system-level theories
Genetic theories
- best evidence is the fixed differences between species in length of life span. (120 years)
- can be part of deviation amplification theory
1) Programmed cell death (apoptosis)
Apoptosis- a gene that regulates sudden cell death, used for T-cells after task is in
our immune system is complete
- Genetic material is not static, always turning on and off depending on need to synthesize proteins
- Damage to these proteins may be a reason for cancer.
- Senescence- biological aging of cells and genes as well
- Hayflick found that fetal cells divided faster than adult cells
- Since cells that replicated slower had disease characteristics, life span and number of times a cell will
- replicate shows a positive correlation
Telomeres- specialized ends of DNA strands that help hold them together during
mitosis. These telomeres do not replicate with the cells so eventually are lost and
cell doesn’t replicate anymore and senesces
Telomerase- is an enzyme that can restore telomeres and is abundant in cancer
cells as well as long telomeres
- Immortality genes regulate cell senescence. Mutations in these genes contribute to infinite cell
divisions.
- Absence of apoptosis and senescence could shorten life and is a form of antagonistic pleiotropy-
helpful and promotes reproduction in early life but may have harmful effects in later life.
2) Stochastic (random) Processes
Hayflick's Theory- argue there may simply be a limited number of times that a cell can replicate
without error. So aging may be a function of random errors.
- Replication error= DNA is susceptible to damage by environmental factors (cigarette, radiation)
- Damage can impair a cell’s ability to synthesize proteins or its ability to respond to regulation
- Backup (turn off damaged segment turn on identical backup, or correct the error). However, the cell
runs out of backups eventually and cell may replicate with these impaired segments.
- Mitochondrial DNA is susceptible to damage since its close to reactive oxygen. So cells such as heart,
brain and muscles have damaged mitochondrial DNA in later life. Drives the cell for apoptosis
3) DNA Repair Mechanisms
- Damage activates transcription and replication
- During replication, there are several checkpoints and if an error is caught, replication stops.
- Primary repairs are (excision repair, nucleotide excision repair, mismatch repair of strand breaks)
- Sometimes errors can escape detection and if it is too severe it can cause apoptosis
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