Aging occurs at the cellular level, at individual organ levels and at the entire whole body organism level when internal constancy can no longer be maintained. Aging is a biological process which occurs over a specific deteriorative chronology in all living cells.
(In 1961, in contradiction to what was thought at the time, Leonard Hayflick and Paul Moorhead discovered that human cells derived from embryonic tissues can only divide a finite number of times in culture.)
These age related changes also result in the increased incidence of specific diseases; i.e., cardiovascular and cerebrovascular, diabetes, ocular, hypertension, etc.
Overall accelerated senescence does not set in until after reproductive maturity. It appears evolution doesn't care how quickly one ages after reproduction has taken place but hypothetically, there are some conditions which slow down the aging process prior to reproduction. William R. Clark in A Means To An End (99), writes, "From a purely biological point of view, senescence is nature's backup plan, if we do not die from external accidental causes, then ultimately we will die from the cumulative effects of internal senescence..." He goes on to say, "But accidental and natural death are intimately intertwined in the life history of every species...The gradual physical weakening that accompanies aging will make an animal more likely to be caught by a predator; diminished immune capacity can make us more susceptible to infectious disease. Moreover, different forms of senescence can interact; decreased immune function, for example, can also make us more susceptible to purely internal diseases such as cancer..."
Advances in the field of biomedical gerontology have indicated these aging processes to be both intrinsic and extrinsic; that is, it is influenced by both intrinsic and extrinsic factors, i.e. genetic, lifestyle and environmental - all of which influences the rate of aging.
Genetic differences are deterministic but environmental conditions vary; as do accidents, exposure to chemicals, stress, and to other factors which are not pre-determined.
"Elderly people look and behave differently than people in the early and peak years of their lives...Even the brain gets smaller, shrinking by up to 10 percent in women, and slightly more in men..."
One of the most noticeable changes occurs in the skin which loses elasticity and muscles which lose tone. There is a loss of subcutaneous fat; the skin becoming thinner with age, changes in collagen and elastin - resulting in increased wrinkling. And, who hasn't noticed those age spots? Besides having a very noticeable effect they have a psychological, emotional impact - a reminder that everything must eventually end. Oil glands slowly lose their function, skin texture becomes rough and loose. And not least of all, the tendency to become confused; diminished mental capacities, etc - difficulty getting up and sitting down and unsteady gate. And there is urinary incontinence. These changes are devastating to everyone as they grow older.
The cardiovascular system begins to break down. There are other signs of degenerative function. Coordination is greatly diminished. And it feels like time speeds up. The days fly by for the elderly. As irrational as that sounds it does appear that way because it feels that way.
We break down. The body just breaks. It is harder to maintain internal constancy. Cells accumulate junk and when you wake up in the morning; if you are lucky enough to wake up, your entire body hurts. You have pain where there was none before. You become aware of certain things that are going on in your body; your need for laxatives or bowel softeners - or you begin to rely on prune juice the night before or with breakfast. And, you need to take something to help you sleep.
The nucleus of your cells hold your DNA and they are wrapped tightly around protein to protect them from cosmic rays (And what does it matter because you are not likely to reproduce anymore anyway - you are too old). The DNA isn't as neatly packaged as it was when you were young. Nothing about you is as neatly packaged as it once was.
You are atherosclerotic. That means the lumen in your arteries are like sludge; they are hardening. The inner lining of those arteries are becoming thicker and not so flexible. That is the pathway along which you deliver blood which is the transport for nutrients and oxygen to your heart and brain (Veins carry carbon dioxide back to the lungs to become oxygenated again). And if you don't get that oxygen to your brain you are not going to be able to remember as well as you once did.
As you senesce your arteries become thicker and clogged with oxidized fatty deposits, including cholesterol and this causes less blood flow. The heart is likely still working well, but the arteries are not doing so good.
You are also subject to other aging processes, like gangrene and strokes. And, you fall more often. Your immune system is less likely to fight off an invasion from pathogenic microbes. You are getting older. -- You are old Jack.
Hank Roth
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