Ageing
time as the thyroid hormone produced is less than the thyroid hormone being metabolized. These changes in the endocrine system, causing diseases like diabetes or death, were thought to be programmed by our genes, which also supports the argument of programmed senescence theory.
Figure 1. Level of testosterone through different ages
One of the other pieces of evidence that support the programmed theory was the immunological theory suggested by Louis Pasteur in the late nineteenth century. The idea that this theory was trying to proclaim is that our body's immune system weakens as we get older, no matter how good the living conditions are. This leaves us more susceptible to catching disease or even developing cancer. Scientists have found that the number of B lymphocytes in our body decreases as age increases. While the number of T lymphocytes stays constant throughout life, the number that is dividing and functioning declines as we age. 5 The last idea which complements the programmed theory is programmed longevity, which argues that ageing results from the sequential switching on and off of special genes in our bodies. In this view, ageing is controlled by our own genes. An example which supports this statement is our telomere. It is located at the end of our chromosomes and is responsible for preventing the loss of useful genes in each DNA replication, as there are always some gene losses through cell division. As the cell divides, the telomeres shorten, leading to eventual gene losses. Cancer cells contain the mutated genes, which can produce an enzyme called telomerase which maintains the length of telomeres, so cancer can continue dividing. This gives evidence to suggest that our telomerase genes are not switched on, and cells are genetically programmed to cell death. 6
5 Fulop, T. et al. (2014) ‘On the Immunological Theory of Aging’, in Interdisciplinary Topics in Gerontology 39: 163- 176. doi:10.1159/000358904. 6 Longo, V. (2019) ‘Programmed longevity, youthspan, and juventology’, Aging Cell .18.1: e12843. doi:10.1111/acel.12843; see also Shammas MA. Telomeres, lifestyle, cancer, and aging. Curr Opin Clin Nutr Metab Care . 2011;14(1):28-34. doi:10.1097/MCO.0b013e32834121b1.
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