In one sense, most of the substance of our body really doesn’t continue to get older during our life: a great many of our body’s parts are constantly repairing and replacing themselves. The epidermal cells that cover the entire surface of our skin, for example, never get older than one month. New cells are continually produced (by cell division) deep in the epidermis, while the older ones continually slough off at the surface. Similarly, the cells lining our intestines completely replace themselves every 4 days; our red blood cells are entirely replaced about every 90 days; and our white blood cells are replaced about every week. Even cells that never (or rarely) divide, such as cardiac muscle cells and brain cells, turn over molecule by molecule. It is believed that little or nothing in our body is more than about 10 years old. Thus, thanks to cell turnover and replacement, most of the organs in the body of a 90-year-old man are perhaps no older than those of a child. Indeed, you might say our body never actually grows older. francisakenami.blogspot/2014/12/why-cant-people-live-for-over-900-years.html
Posted on: Thu, 25 Dec 2014 18:53:13 +0000
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