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The human body is only 10 years old

The age that appears on our driver’s license is one thing; the age of our body is something quite different.

Although we may officially be going on a hundred years of age, our organism probably has not reached age ten, and in the case of many internal organs even less.  The hand you are writing with, the nose that is holding up your glasses or these legs that you are crossing in your chair are not the same organs that you had ten years ago, although they are nonetheless parts of your body.

The secret is the constant renovation that all of our cells undergo without our being aware, although Jonas Frisen, a biologist from the Karolinska Institute in Stockholm who is an expert in T-cells, has perfected a method for calculating the age of human cells using Carbon 14 which permits use to analyze separately each piece of our marvelous organism.

According to Frisen, the median age of all of the cells of an adult ranges from 7 to 10 years, no more than that, subject to confirmation of whether brain cells (which until recently were thought not to reproduce themselves although recent experiments prove the contrary) are practically the only cells that accompany us from birth to the grave.  Even though when we look in the mirror we see our body as a structure that is generally fairly permanent, a large part of it is in a constant state of flux, shedding old cells and substituting them with new ones.  We easily appreciate this with our nails or hair, but every fragment of our physique goes through the same process, depending on the work that it does.

Thus the cells that line the stomach only last three days, at the end of which they are eliminated and substituted with new ones.  Red blood cells last on average about 120 days before being sent to their particular cemetery in the spleen.  The liver, filter for all the toxins we ingest, lives between 300 and 500 days before being completely renewed.  Other organs or tissues last longer, like the muscle cells of the ribs or the interior of the main part of the intestine, which reach an average of more than 15 years.  The entire skeleton of an adult is renewed in ten years.

The question is:  if the body constantly renews its tissues, why does it not continue its regeneration forever, but instead decay with age?  According to some experts, the cause is the mutations and degradation that accumulates in DNA as the years go by.  Others also blame DNA, but that of the mitochondria, which lack the repair mechanisms that chromosomes have.  A third theory is that T-cells, the source of new cells in all tissues, become weak with age.