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Ageing is an inevitable physiological process which leads to a decline in biological functioning and subsequent adaptability towards metabolic stresses. The term "old age" is often ambiguous, and people seem to have a different kind of understanding when we are describing someone as old. This word had a different starting age when we considered various factors such biological, employment, morbidity, mortality, retirement and sociological component. Even though the exact age to be classified as old is never determined, people who aged between 60-65 years old can usually be retired from their respective services. This age range is the definition of old age which is being used for administrative purposes, and it's not rigid; the number can change accordingly.
Gerontology and Geriatrics focus on the disease and normal ageing process which look upon on a few critical issues such as:
- Economic and social burden caused by the increase of ageing population.
- Physiological component of ageing which include intellect and personal adjustment.
- Healthy ageing, pathological ageing and the disease process.
- The general aspect of ageing in all animals.
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The ageing process is not usually explained or identified by physical weakness because this factor is affected mostly by human experiences; i.e. if you've exercised continuously and eaten well when you are younger, you will have a much higher physical strength compared to the average power possessed by people in an ageing population. The ageing process can be influenced by natural physicochemical means or by a random organismic process caused and intensified by specific disease processes which can lead to death.
> Gerontology can be defined as the science of the finitude of life as expressed in the three aspects of longevity, ageing, and death, examined in both evolutionary and individual (ontogenetic) perspective. Longevity is the span of life of an organism. Ageing is the sequential or progressive change in an organism that leads to an increased risk of disability, disease, and death. Senescence consists of these manifestations of the ageing process.
In this modern world (21st century), the lifespan of a human has increased by a more significant number (around 67 years average) compared to the lifespan in the 20th century which has been estimated around 30-45 years. This increment can be caused by an improvement in the healthcare system, nutrition, reduced infant mortality rates and changes in the standards of living. It has been understood that the life expectancy of any people who practised a healthier lifestyle, i.e. exercise regularly, eat healthy food and sleep adequately, would soar up higher which can reach as high as 100 years old like the Okinawan people in Japan.
There are a few theories which have been reviewed over the years to explain better the physiological phenomenon one has to go through in an ageing process. These theories can be classified into two major categories; either it's influenced by the genetic or not.
## The influence of genetic on the ageing process
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The role of telomere has been the primary component of this theory which determines the ageing process. Like the colour of our eyes, ageing is has been predetermined inside the repeated coding segment of deoxyribonucleic acid (DNA) which occurred at the end of the chromosome. This theory came about after careful observation of identical twins which have an almost similar lifespan compared to a non-twin sibling. A child who has long-lived parents were most likely to live longer than any average people.
The number of repeated sequences at the chromosomal ending determines the maximum age an individual could achieve. As our cells continuously divide, these multiple repeats are slowly lost which lead to a reduced size of telomeres. If you would like an example to understand this better, imagine you were holding a 100 USD note, if you divide the value by two, you will have two 50 USD notes. The total amount is the same, but if we inspect each note, obviously, it would have lesser value than a 100 USD. A cell would be dividing for eternity (metaphorically), but when the length of telomeres has reached a specific size in which division is no longer possible called a crisis point, the cell will die. This event contributes to the ageing process.
Telomeres which are the principal factor which determined the ageing process can be influenced easily by an alteration through mutation. An enzyme called telomerase has a vital role in preventing overshortening of the telomeres during cell division, but a mutation in a gene called the Telomerase RNA component (TERC) which encodes the RNA sequence of the telomerase, can overshorten the telomeres which consequently increased the rate of the physiological ageing process. This variance of TERC has a paradoxical function compared to the normal one, so people who carry this particular mutated enzymes can be much older regarding their biological age compared to their peers who share the same chronological age.
Telomere's mutation can be one of the most critical factors which can influence the process of ageing. If there is a coding error within the repeated sequence, these will cause the formation of a defect protein which will deter normal cellular functioning.
## The influence of non-genetic factors on the ageing process
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There are a few theories which focus on the other factors which can influence the expression of the genetically formed programs which contributes to the healthy ageing process. It's relatively easier to measure ageing process by judging the physical attributes such as skin, strength etc. rather than focusing on the cellular processes.
**Wear and tear**: This is an assumption which compares cellular function to a machine which will wear out over a period. Even though theoretically, the concept appears correct, but most of the animals can repair themselves which contradict the original idea of use, wear and tear. In another theory which is explained by this assumption is the accumulation of waste products can interfere with the normal cellular functioning. These waste products are called age-pigment and can be commonly observed in the muscle and nerve cells of an animal and humans.
**Cross-Link**: The formation of a cross-link between a molecule of collagen can reduce the elasticity blood vessels, tendon and even skin. This process was assumed to occur in another molecule, such as an enzyme, which can give rise to a dysfunctional protein that could affect cellular functioning.
**Autoimmunity**: Having an immune system can be a blessed when they were defending your body from a disease agent, but when they attack healthy tissue, it's a different story. The component of the immune system is unable to differentiate between the foreign invaders and self-proteins. However, the validity of this theory is unknown due to lack of the experimental evidence.
**Glycation**: Glucose can cause ageing. In a process called glycation, glucose would interact with proteins in the blood vessel which yield an advanced glycation end product. They produce a cumulative effect of ageing on an individual over the years which could shorten life by a few years. This compound is usually found in a diabetic patient.
**Oxidative damage**: In the 1950s, Denham Harman, proposed the first theory of ageing caused by a compound which is called as the reactive oxygen species. This compound can cause oxidative damage, and for those who forget or doesn't know, oxidation is the removal of electrons from a molecule to another which made them highly reactive and unstable. The theory was then expanded to include an organelle called mitochondria which contributes mainly to the production of radical oxygen species. Mutation in the mitochondrial DNA can increase the production of oxygen radicals which could impair the original function of providing cellular energy. This could lead to cell dysfunction and degeneration. Calorie restriction has been attributed to the production of less reactive oxygen species which could slow the ageing process.
# References and further reading materials
- Kara Rogers Petra Simic Leonard P. Guarente (1998, September 8). Encyclopedia Britannica. Ageing Life Process. Retrieved March 4, 2018, from https://www.britannica.com/science/aging-life-process
- Pajares (2002). UKY.Edu. Overview of Social Cognitive Theory
and of Self-Efficacy. Retrieved March 4, 2018, from https://www.uky.edu/~eushe2/Pajares/eff.html
- Wikipedia. Ageing. Retrieved March 4, 2018, from https://en.wikipedia.org/wiki/Ageing
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