Definition
Human aging is a biological process, no
one can stop, but delay it. It is possible that one person has a
physiological younger than his or her biological if one engages in
healthy living life style and eating healthily by increasing the intake
of good healthy food such as whole grain, fruits, vegetables, beans and
legumes, etc. and reducing the consumption of harmful foods, such as
saturated fat, trans fat, artificial ingredients, etc.
Theories of aging
What
cause aging? The question that has been asked throughout the human
history, but it doesn't seem to get any answer but raises many more
unanswered question. While many theories try to answer the question by
related aging to tear and wear of the body, others deal with how the
organs and systems in the body develop and deteriorate overtime, etc.
1. Somatic mutation theory
In
this theory, aging is due to our inherited genes that come directly
from our parents. Since the conception occurred, our body cells continue
to divide and replication themselves. Since the division and
replication are a life long precess at some point, for what ever reason,
if cells division and replication can process incorrectly, leading to
mutation of incorrect copy of DNA. Although the cause of this incorrect
process are unknown, but researchers found that exposures to toxins,
radiation or ultraviolet light, artificial ingredients, unhealthy life
style, etc. can increase the risk of cells mutation and the cells copied
incorrectly can mutate themselves, leading to accumulation of incorrect
gene cells that trigger a chain reaction of an auto-catalytic nature in
producing more and more fincorrect gene cell, until it finally is
brought under controlled, this processes can lead to aging. As an
organism, the immune system tries to destroy or scavenger these mutated
genes but at some points, it is over whelming, leading chronic age
related diseases.
2. Error catastrophe theory
The
error catastrophe of aging, originally proposed by Leslie Orgel in
1963. Our body immune system helps to maintain the structural integrity
of DNA not only for cell survival but also for the transfer of correct
genetic information to the daughter cells. Error catastrophe indicated
that alterations DNA and the incorrect placement of amino acids in
protein synthesis could result in a progressive degradation aging as a
result of these abnormal protein are no longer functioning as chemical
passengers or signalers.
3. Protein glycosylation
Protein
glycosylation is a result of chemical reaction of glucose with vary
proteins, including enzyme, elastin and collagen in the blood. The cross
linked protein glycosylation leads to cell to cell adhesion causing
stiffness and rigidity of individual cells, reducing the cells function
in taking nutrients and expelling waste.
If the cross link protein
glycosylation occurs in the elastin and collagen, it will cause brittle
skin, causing aging, but it happens in the organs it will be more
serious and sometimes life threatening.
4. The neuroendocrine theory
First
proposed by Professor Vladimir Dilman and Ward Dean MD, this theory
postulates on wear and tear of the neuroendocrine system. In
neuroendocrine system, the master pituitary gland secrets hormones to
direct other glands in secreting their hormones and works conjunction
with the hypothalamus glands form a command post in the nervous system
in closely direct the function of most of the body functions.
but as
we age, the hypothalamus loses its ability as a hormone regulator as its
receptors of which uptake other gland hormones become less sensitive to
them, including sex hormones, DHEA, serotonin, melatonin, etc.
As for cortisol, a hormone secreted by the adrenal glands due to stress, is produced with abundance as we age.
5. Immune system decline theory
As
we age, our immune system is weakening that cause us become vulnerable
to the dangerous pathogens, including microbial and viral invasion.
Within the immune system, the thymus glands which play an important role
in helping formation of the immune system scavenger that reduces the
function of immune system further that allow irregular cell growth cause
of aging spot, tumors, cancer, infection, inflammation and onset of
chronic illness.
6. Genetic programming theory
Genetic
programming theory propose that aging is programmed as the cells cycle
in our body are also genetic program since their inception. the
explanation is that all the cells are undergoing certain time in
division over the a said amount of time before dying, leading to
conclusion that people with the long live genetic program live longer
than others who do not.
The theory also emphasizes the genetic
diseases as a result of genetic programing diminished life span,
regardless external and internal influence.
Further refinement of the
programmed senescence theory was developed by Bernard Strehler, who
proposed that as cells are program to perform specific functions within
the organism that cause them to lose some of the ability to duplicate
their genetic information, leading to aging.
7. Hayflick limit
The
Hayflick limit (or Hayflick Phenomena) theory discovered by Leonard
Hayflick and a biologist in 1966. In vitro study, the number of times a
fibroblast diploid cells will divide before it stops. The discover is
conferring a major hypothesis if the cell division can prolong in a
infinite matter without conditions which cause damage of the cells, then
organism can liver forever.
Exceptions:
Stem cells
Since
stem cells can continue to regenerate new cells for the entire lifespan
of the organism, without limit, thus constituting a notable exception
to the Hayflick limit theory.
Cancer cells
Cancer cell in
biological aspect, have found a way around the limit by becoming a group
of immortalized cells produced from cell division that have no limit as
to how many times this immortalized cell division might take place.
8. The telomerase theory
The
tolomerrase theory is a continuation of support to the Hayflick limit
(or Hayflick Phenomena) theory involved in telomeres and telomerase.
Telomeres are the structure at the end of the chromosome. As each time
the cell divides, its telomeres is shortened, at certain length, the
cell stops division and goes into senescence.
The experiment shows,
the cell senescence can be reversed by controlling the genes of
telomerase autocatalytic nature, which in turn, promotes the forever
cell division capacity
9. The free radical theory
A
free radical is any atom or molecule that has a single unpaired
electron in an outer shell and highly reactive to react with other cell,
which in turn, causes oxidative damage to the enzymes, other protein,
unsaturated fatty acid, phospho-lipids, DNA and RNA, etc., leading to
aging of the organisms, as a result of widespread damage due to set of a
chain reaction auto-catalytically after attacking the lipid bilayers of
the cell walls.
10. Other theories
a. Rate of living and lifespan
Rate
of living is defined that a bigger organism, the longer it lives with
human is one of the exception due to its slower rate of metabolism and
lower rate of free radical activity, leading to low levels of age lipid
pigment, resulting in longer life span. Experiment show that there
100,000 free radicals hit everyday in rat, comparing 10, 000 in human.
b. Caloric restriction
Caloric
restriction hypothesis suggested in a study of young rat showed that if
a rat is put into restricted diet with given of necessary nutrients, it
lives longer than those were allowed to eat freely. With the result
also the same in the old rat, the theory also suggest eating less may
cause less toxins in the body that affects the immune system and reduces
the risk of hormone change, leading to free radicals cause of aging.
c. Age spots
Age
spots are mainly composed of lipofuscin and lipopigment caused by
reaction of free radical and peroxidation, leading to the formation of
age spot, as a result of oxygen species interact with autophagocytic
degradation occurring inside the lysosomes.
d. Protein oxidation
Protein
oxidation cay affect protein function in normal and pathological
processes as a result of postranslation protein being alter by reduce
oxygen species (ROS) cause of damage to enzyme, leading to dysfunction
of its role resulting in aging.
e. Fast track of aging
The theory suggest that there are many of diseases and syndromes of which can contribute to faster track to aging
* Hutchison-Gilford syndrome
It
is an extremely rare genetic condition wherein symptoms resembling
aspects of aging are manifested at an early age. Those born with
progeria typically live to thirteen years, although many have been known
to live into their late teens and early twenties and rare individuals
may even reach their forties due to genes mutation.
*Werner syndrome
It
is Adult progeria, an disorder causes the appearance of premature
aging. The syndrome does not develop until they reach puberty is caused
by autosomal recessive disorder due to alter gene on chromosome 8.
f. Altered genes
Alter genes are the work of Friedman and Johnson 1988 " .... the effect of elevated expression of SIR2 in yeast appears to be conserved in C. elegans (Tissenbaum & Guarente 2001) and Drosophila (Rogina & Helfand 2004),
and mutations in genes encoding components of the target of rapamycin
(TOR) pathway also extend the lifespan in all four organisms... "
"...
It was originally suspected that extension of lifespan by reduced IIS
might turn out to be a worm peculiarity. This was because mutations in
genes in the IIS pathway can also cause the worms to enter a type of
developmental arrest (dauer), normally seen only in response to low food
or crowding (Riddle & Albert 1997).
Dauer larvae are long lived, and the long life of IIS mutant adult
worms could therefore have been a result of re-expression in the adult
of the genes that make the dauer larva long lived...."
g. Free radical connection
Free radical is any atom or molecule that has a single unpaired electron in an outer shell and accumulation of free radical damage over time can cause aging. Theory is first proposed by Denham Harman in the 1950s and in the 1970s extended the idea to implicate mitochondrial
production of reactive oxygen species into the 1970s. Study showed that
nutant strains of the roundworm that are more susceptible to free
radicals have shortened lifespans, and those with less susceptibility
have longer lifespans
If free radical causes damage to the DNA
repaired enzymes, it can increase the risk of unrepaired DNA damage,
leading protein synthesis incorrectly. In fact, free radicals can
inflict damage to all celsl in body such as endocrine glands, leading to
decreasing of hormone secretion, resulting in aging and Kupffer cell in
liver, causing endotoxins accumulated in the blood, leading to more
free radicals attacks the immune system, etc.
10. Hormone depletion
The
researchers found that if an decrease or absence of the pituitary gland
hormones mice is given enough amount of pituitary hormones, it lives
longer than a control group of normal mice as it stimulates the
production of growth and other hormones such as prolactin,
adrenocorticotropic hormone, thyroid-stimulating hormone, etc.
11. etc.
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