General Theories of Ageing

Samira Hamzeh 3rd year pharmacy at Jinan University

ABSTRACT In this review paper we discuss all the theories of aging that are proposed. We begin by a little introduction then we mention each theory with little explaining about the bases of each theory and finally we make a little conclusion where we open another door of discussion.

INTRODUCTION

Everything in this life begins small and with time will be bigger and bigger so everything fits under the theory of ageing and it is true that there is no common definition to the theory of ageing, but depending on the discipline, the phenomenon of ageing takes a different definition. Biological ageing is made up of a number of undesirable processes. There are multiple processes of ageing that result in a decline in efficiency of the organism and end in its death.

Ageing, particularly in the psychosocial sciences often includes a desirable process of maturation that, is, acquiring a desirable quality such as wisdom.

The biological theory of ageing
Biological theory:
- PRIMARY AGEING (developmental genetic theory)
- SECONDARY AGEING (stochastic theories)

PRIMARY = decline in functions which are genetically controlled.
SECONDARY = random changes resulting from acquired disease and trauma.

DELIBERATE BIOLOGICAL PROGRAMMING
Numerous studies demonstrated that normal cells have a memory for the number of duplications to be encoded in the genetic material. In ageing not only is the neuron lost, but also there are alterations of neuronal synapses and networks.

GENETICS OF HUMAN AGEING
Females outlive males because the y chromosome does not contain sufficient genetic material. Mitochondrial genes which are inherited from the mother are important to aerobic respiration and age changes.¹

THE AGEING CLOCK
The hypothalamus where there is alteration in the responsible nuclei clusters of cells and in the functions of these cells, plays an important role in the losses of homeostatic mechanism in the body. Van Gool and Mirmiran propose that our biological rhythms become desynchronized as we age.

THE FREE RADICAL THEORY
Free radicals (molecular fragment as it has an unpaired electron ) have been linked to DNA damage, the cross - linkage of collagen, and the accumulation of age pigments.^2,3

THE ACCUMULATION OF WASTE
With time there is accumulation of lipofuscin (pigment) in neurons but limited to the cells that are capable of dividing, while there is no evidence that it may be harmful to these cells.⁴

THE IMMUNE SYSTEM AND AGEING
A small number of immunologically competent cells produce antibodies which might result in death or damage in a large number of cells including neurons; anti-brain antibodies are believed to be related to neuronal injury in senile dementia of the Alzheimer tyoe. Interleukin-2 declines with age and it appears that the administration of IL-2 may retard the human ageing processes.⁵

PSYCHOLOGICAL THEORIES OF AGEING
The main areas that have been studied by psychologists can be placed into three broad categories:
- COGNITIVE
- PERSONALITY
- COPING MECHANISM

COGNITIVE
It is the range of human intellectual functioning⁶. Adults with high intelligence and education will show minimum decline in their performances with increasing age, while a significant decline is observed in adults with lower intelligence and age. There are several theoretical models of memory functioning. Intellectual performance seems to be strongly influenced by physical health. Perlmutter sees decline neither inevitable nor universal and says that some cognitive skills may improve or may be acquired as one ages. However as one reaches the point of "terminal drop" which is a curvilinear decline related to the distance of death rather than old age itself, there will be a decline in intellectual functioning. Schaie's stage theory of adult cognitive development attempts to formulate four cognitive stages in sequence:
- First stage: acquisitive in childhood and adolescence.
- Second stage: achievement in young.
- Third stage: responsible and executive in the middle-aged individual.

Ribot advanced the cognitive regression hypothesis which hypothesized that the structures first formed are the last ones to degenerate in old age. Also Ribot's law is based on the fact that older adults have an easier time learning and retrieving dated items.

PERSONALITY THEORIES
There is conflict between theories according to personality and some proposed an antistage theory of ageing where personality, development, and adjustment are affected by historical events throughout the life cycle. Others say that the elderly may find either ego integrity through satisfaction with past life or despair and adjust over past failures and many other theories have been reported according to personality.

SOCIAL THEORIES OF AGEING
Social theories are divided into those that examine the relationship of the older person to society and those that study the role and status of the elder. Cumming and Henry claimed that the withdrawal of the elderly from their previous societal roles, with reduction in all types of interaction, was desirable and helped the elderly to maintain life satisfactions. In contrast the disengagement theory proposed that the activity contributes to health and life satisfaction. Also there are many sociological theories that have varying degrees of validity.

THE WEAR AND TEAR THEORY
Dr. August Weismann believes that the body and its cells were damaged by overuse and abuse. Wear and Tear theory is not confined to our organs; however, it also takes place on the cellular level.

Abuse will only wear them out more quickly. Likewise as the body works our cells feel the effect, no matter how healthy our life style. When we are young the body's own maintenance and repair systems keep compensation, the effects of both normal and excessive wear and tear.

THE NEUROENDOCRINE THEORY
This theory focuses on the neuroendocrine system, the complicated network of biochemicals that are responsible for the release of our hormones and other vital elements. Different organs release hormones, all under the governance of the hypothalamus, a walnut-sized gland located within the brain.

The hypothalamus responds to the body's hormone levels as its guide to regulating hormonal activity. Hormones are vital for repairing and regulating our bodily functions, and when ageing causes a decline in our body's ability to repair and regulate itself as well. The drop in production of any one hormone is likely to have a feedback effect on the whole mechanism.

Thus hormone replacement therapy, a frequent component of any anti-aging treatment, helps to reset the body's hormonal clock and so can reserve or delay the effect of aging.

HAYFLICK LIMIT THEORY
Hayflick theorized that the aging process was controlled by a biological clock contained within each living cell. Nutriton seemed to have an effect on the rate of cell division, overfed cells made up to 50 divisions in a year, while underfed cells took up to three times as long as normal cells to make divisions. This improper functioning of cells and loss of cells in organs and tissues may be responsible for the effect of aging.

DEATH HORMONES THEORY (DECO)
Dr. Donner Denckla was convinced that the "death hormones" or deco released by the pituitary gland contributed to the loss of neurons. The resulting changes in metabolic rate bring and accelerate the process of aging.

THYMIC-STIMULATING THEORY
Scientists investigating whether the disappearance of the thymus contributes to the aging process weakening the body's immune system. Thymic hormones may also play a role in stimulating and controlling the production of neurotransmitters and brain and endocrine system hormones, which means they may be pacemakers of aging itself, as well as key regulators responsible for immunity.

MITOCHONDRIAL THEORY
Mitochondria are the energy-producing organelles in the cell that are responsible for producing energy. They produce cell energy by a process that leads to the formation of potentially damaging free radicals. Accumulated DNA damage over time is a contributing factor to disease.

ERRORS AND REPAIRS THEORY
Machinery for making protein in cells is so essential; an error in that machinery could be catastrophic. Therefore the accumulation of these flawed molecules can cause diseases and other age change to occur.

REDUNDANT DNA THEORY
The redundant-DNA theory blames errors accumulating in genes for age changes. But as these errors accumulate this theory also blames reserve genetic sequences of identical DNA that take over until the system is worn out.

CROSS-LINKAGE THEORY
Johan Bjorksten applied this theory to aging diseases such as sclerosis, a declining immune system and the most obvious example of cross-linking, loss of elasticity in the skin. With age however the number of cross-links increases, causing the skin to shrink and becomes less soft and pliable. It is thought that these cross-links begin to obstruct the passage of nutrients and waste between cells.

Cross-linking also appears to occur when older immune systems are incapable of cleaning the excess glucose in blood, which reacts with proteins causing cross-links and the formation of destructive free radicals.

CALORIES RESTRICTION THEORY

A high nutrient low-calorie diet can dramatically retard the functional, if not the chronological aging process. Walford stresses the importance of not only the high-low diet but also moderate vitamin and mineral supplements coupled with regular exercise.

GENE MUTATION THEORY
Scientists investigated the role of mutations in aging, radiation not only increased animal mutation but it also accelerated their aging process as well.

THE RATE OF LIVING THEORY
If energy is consumed quickly aging is hastened. Other rate-of-living theory focuses on limiting factors such as amount of oxygen inhaled or number of heartbeats spent.

ORDER TO DISORDER THEORY
"Directing most of our energies to fulfilling a genetically determined plan for the orderly production and arrangement of an enormous number and variety". After sexual maturation however these same energies start to diminish in efficiency. Disorder occurs in molecules in turn causing other molecules to produce errors and so on.

THE TELOMERASE THEORY OF AGING
Telomerase are sequences of nucleic acids extending from the ends of chromosomes which act to maintain the integrity of our chromosomes. Every time cells divide telomerase are shortened, leading to cellular damage and cellular death associated with aging.

CONCLUSION

Many, many theories have been proposed to analyze the ageing process. All these theories take the subject from different or common pathways but the question is: is there an eternal youth and to what limits can we preserve this youth?

REFERENCES

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