Aging
Partly in response to a letter from a correspondent who proposes that it should be scientifically possible to revive people who have had heart attacks and/or are brain dead (such as Ariel Sharon), I write the following.
There are three processes that lead to what we call aging. The first and most fundamental is at the cellular and molecular level and is known as apoptosis or programmed cell death. This process was discovered in the 1950s by a British cellular biologist, but was ignored for many years. If you think about it it makes sense, since cells are dividing, the organs would continue to grow to enormous sizes unless cells were also dying and being replaced at a more or less comparable rate. When cells are damaged or get "old" (i.e. after a limited number of divisions) they tend to self-destruct, they produce enzymes that degrade their own cellular structures. Then there are mutations within the cells that over a long period of time accumulate and cause genetic diseases that can be fatal, such as cancer, that is more prevalent as people live to older age. One of the features of cancer cells is that although they are aberrant, they evade apoptosis and continue to live, i.e. in effect they become immortalized.
One should not forget that all of our tissues are turning over, being degraded and re-synthesized (blood takes about 5 days to be replaced). This raises serious questions, such as are we the same person we were before all our systems were regenerated. But, the only tissue that does not do this is nerve tissue, the brain and nerve cells are more or less unchanging throughout our life, hence we can retain memories from an early age, which otherwise would be lost if the tissues that retain the memories were being replaced (although they are when damage occurs).
A major cause of aging is the physical breakdown of macroscopic structures, such as muscles (heart), collagen (e.g. spinal disks), joints (arthritis) and so on. This might be called "wear and tear" and particularly affects the digestive, urinary and reproductive systems. The effect of carrying around a lot of extra weight as people become fatter and less fit cannot be ignored. At a certain age most women stop producing estrogen and men testosterone. The loss of these hormones, even though one can have hormone replacement therapy (HRT), causes irreversible changes in the body (such as osteoporosis). Another result is greying of the hair and hair loss, which are perfectly natural processes. There can also be dementia due to localized damage to the brain or strokes, that are micro-embolisms in the brain, or Alzheimer's disease.
Finally, at advanced age or as a result of advanced disease, there is a process called cachexia that mimics the process of apoptosis, but on a macroscopic level. All the body's organs begin to break down, including the brain, and so mental and physical well-being and quality of life are impaired.
So to those of us who exercise and go to the gym to keep active and healthy, keep trying, but don't expect it to evade eventual aging.
There are three processes that lead to what we call aging. The first and most fundamental is at the cellular and molecular level and is known as apoptosis or programmed cell death. This process was discovered in the 1950s by a British cellular biologist, but was ignored for many years. If you think about it it makes sense, since cells are dividing, the organs would continue to grow to enormous sizes unless cells were also dying and being replaced at a more or less comparable rate. When cells are damaged or get "old" (i.e. after a limited number of divisions) they tend to self-destruct, they produce enzymes that degrade their own cellular structures. Then there are mutations within the cells that over a long period of time accumulate and cause genetic diseases that can be fatal, such as cancer, that is more prevalent as people live to older age. One of the features of cancer cells is that although they are aberrant, they evade apoptosis and continue to live, i.e. in effect they become immortalized.
One should not forget that all of our tissues are turning over, being degraded and re-synthesized (blood takes about 5 days to be replaced). This raises serious questions, such as are we the same person we were before all our systems were regenerated. But, the only tissue that does not do this is nerve tissue, the brain and nerve cells are more or less unchanging throughout our life, hence we can retain memories from an early age, which otherwise would be lost if the tissues that retain the memories were being replaced (although they are when damage occurs).
A major cause of aging is the physical breakdown of macroscopic structures, such as muscles (heart), collagen (e.g. spinal disks), joints (arthritis) and so on. This might be called "wear and tear" and particularly affects the digestive, urinary and reproductive systems. The effect of carrying around a lot of extra weight as people become fatter and less fit cannot be ignored. At a certain age most women stop producing estrogen and men testosterone. The loss of these hormones, even though one can have hormone replacement therapy (HRT), causes irreversible changes in the body (such as osteoporosis). Another result is greying of the hair and hair loss, which are perfectly natural processes. There can also be dementia due to localized damage to the brain or strokes, that are micro-embolisms in the brain, or Alzheimer's disease.
Finally, at advanced age or as a result of advanced disease, there is a process called cachexia that mimics the process of apoptosis, but on a macroscopic level. All the body's organs begin to break down, including the brain, and so mental and physical well-being and quality of life are impaired.
So to those of us who exercise and go to the gym to keep active and healthy, keep trying, but don't expect it to evade eventual aging.
posted by Jack Cohen at 3:31 PM
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