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HLTB01H3S: Health, Aging and the Life Cycle
Department of Health Studies
University of Toronto at Scarborough
Instructor: Anna Walsh.
Term: Winter 2010 Mondays 3 p.m. - 5 p.m.
Lecture Room: Room AA112.
Theories of Aging.
A&G: Chapter 3- Theories of Aging: Biological and Psychosocial Theories.
•Gerontology -has provided facts that are based on systematic observations that
may be loosely grouped into models, but rarely provide any conclusive theory.
•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 progressive loses of biological function
accompanied by decreasing fertility and increasing mortality with advancing age.
This process usually occurs after sexual maturation and continues up to the time
of maximum longevity (life span) for members of a species. Death is the final
event. Although age-related changes occur in every individual in a given species,
different species are known to age at different rates. Note: The rate of aging can
vary between individuals of the same chronological age.
Lifestyles also exert additional influence on the aging process. Aging is caused
by the accumulation of damage to the cells. Some of the causes are unavoidable
such as ultraviolet radiation, free radicals and genetic effects, while others involve
environmental and behavioral influences.
•Many theories and models have been advanced to better explain the aging process
that reflect both the genetic and environmental factors associated with aging.
Theories of Aging
•Aging processes occur at the biological, psychological and social levels.
•There are different theories that reflect each discipline with no general consensus.
•Although we are beginning to appreciate the underlying causes and the factors
that regulate or govern the rate of aging, we are still not certain about why we age.
•Bengtson, Rice and Johnson (1999) They argued that different theories
emphasized different aspects such as: characteristics of the aging population, the
development or aging process and the way in which age is incorporated into
elements of the social structure.
•Gender is one of the strongest predictors of life expectancy with women living
longer than men. Better conditions in sanitation and medical procedures such as
the risk to women in childbirth offered greater improvement for women’s
longevity. The continued difference in life expectancy between men and women
is due to a number of biological, behavioural and environmental factors.
•If change occurs, mechanisms typically exist for countering that change and
returning that organism to a steady state. Classic examples include blood pressure
regulation, heart rate, respiratory rate, glucose regulation and DNA repair. Once a
system has been displaced and homeostasis (steady state; regulation; balance) has
been affected, the deviation amplification mechanisms can take over, accelerating
the change or imbalance Once a system is removed out of homeostasis, then
deviation amplification mechanisms can take over, accelerating the change or
imbalance. Biological processes relevant to aging fall into 2 categories: those that
promote homeostasis (steady state; regulation; balance) and decelerate the aging
process and those that increase the aging process such as that which results from
the effects of free radical damage.
•Psychosocial theories often advance positive and negative changes with age.
•There are many biological theories of aging: 1. Genetic Theory: the maximum life
span of a human being is 120 years. The life span differs between species. 2.
Deviation Amplification Theory: Theory that deals with problems of aging. i.e., a
death gene that regulates suicide cell death = Apoptosis (programmed cell death).
Apoptosis is one mechanism for the destruction of cells i.e. the destruction seen in
the immune system with T-cells. There may be a positive correlation between the
life span of a species and the # of times that a cell will replicate. Telomeres
consist of specialized ends of DNA strands that help them during the stages of
mitosis. In humans the # of times somatic cells can replicate is partially regulated
by telomeres. Telomeres can be restored by an enzyme called telomerase.
Cancer cells have longer telomeres and more active telomerase than normal cells.
The number of times that a cell replicates may also be affected by genes.
•There are certain theories such as that of Hayflick who has argued that there may
be a limited # of times that a cell can replicate without error. DNA repair
mechanisms can be used to correct errors. The DNA in mitochondria may be
particularly susceptible to damage. Mitochondria (part of the cell that deals with
oxidation). DNA damage can occur from a variety of environmental factors such
as radiation as well as from internal processes such as oxidation.
DNA Repair Mechanisms