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The Process of Ageing |
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Healthy Ageing |
What is the Nature of the Ageing Process? The body continually replaces itself. The juvenile cells of nearly all organs divide to replicate themselves as the older cells die. The life of a single cell may last a few days, as is the case with cells lining the bowel - or a few months, as occurs with red cells in the blood. Even the rigid components of the body such as bone, are continually resorbed and laid down anew. Theories of Ageing With an electron microscope it is possible to see chromosomes within the cell nucleus. At the end of each chromosome lies a tail of proteins, called a telomere, which reduces with each cell division. When telomeres are reduced to a critical extent, cells stop dividing and die (apoptosis). Failure of that organ of the body then follows inevitably. This process occurs in all living cells. Within the chromosomes lie genes composed of DNA with amino-acid sequences which carry the code giving us our inherited characteristics. Collectively these give each of us our unique inheritance. They effect our rate of ageing and by the inheritance of these 'longevity' genes, our life expectancy is powerfully influenced. Many conditions that we associate with ageing are, in fact, due to the impaired efficiency with which organs function. Deterioration of function finally reaches a threshold at which, symptoms from joint pains to mental deterioration, appear. Most theories of ageing agree that these changes are due to the accumulation of unrepaired damage in body tissues. In evolutionary terms, different species respond to their environment by prioritising either tissue repair or reproduction and this choice determines the average life expectancy of that species. The body repairs, in preference, those structures for which repair is economic and which are necessary for reproduction of the species. Body tissues which are metabolically costly to repair include damaged DNA in the cell nucleus, damage to the chemical 'factories' (mitochondria) which control cell activity outside the nucleus and abnormal proteins accumulated within the cell and damaged by 'free-radicals'. Free-radicals are chemically reactive molecules produced as by-products of all cell function. While most are mopped up by normal repair processes, there is cumulative damage to cell components such as the cell membrane, DNA and other proteins. The 'free-radical' theory of ageing describes damage by free-radicals as responsible for cancer, respiratory disease, dementia, cardiovascular disease and eye diseases. Exposure to toxins, infections, smoking and high saturated fat intake in the diet increase production and damage by free-radicals.
The immune theory of ageing states that immune function declines progressively as the thymus gland shrinks and its stem cells, those cells from which other cells are derived, are no longer produced. Whatever process dictates the particular mechanism of ageing, there is a progressive and generalised loss of function, reduced ability to respond protectively to stress and a growing likelihood of clinical disease. How each of us ages is determined not only by our genetic make-up but also by the extent to which early development occurs under optimal conditions. For instance the risk of diabetes or cardiovascular disease in the second half of life is strongly influenced by the adequacy of maternal nutrition during pregnancy. The Maximum Life
Span Causes of
Morbidity in Later Life
The Importance
of Lifestyle Longevity relates to a sense of purpose and meaning in life, commitment within a community and a quality of independent mindedness. In many respects the present cohort of 50 and 60 year olds represent a pioneer group. They grew up in the post war years when there was a new spirit of freedom and they have retained a determination to find purpose in the later years of their life. They represent a significantly large section of the community and are, therefore, increasingly influential in economic terms. |