Do people change with time? Of course, you would say, we grow, mature, become old and weak (if we live up to that point), we gain not only knowledge but also experience, our character even changes with age, but in general we remain ourselves from the moment we begin to realize ourselves until death itself.
All this is true, and yet, according to Swedish researcher Olaf Bergman, a member of the Department of Cell and Molecular Biology at the Karolinska Institute in Stockholm, we are not quite ourselves every day, and on average a person finds himself in a completely new (but not foreign) body every seven years. This happens because trillions of our cells are constantly aging; something breaks in them and they need to be replaced.
For example, the cells that line the mouth, stomach, and intestines wear out very quickly and need to be replaced every 2-10 days (you’ve probably noticed how quickly wounds in the mouth or a bitten tongue heal). Skin cells also change every 10-30 days, but it takes about 4 months to completely replace red blood cells in the body.
Sam Bergman, using radioactive carbon analysis, studied the rate of liver regeneration and found that the majority of its cells regenerate within a three-year cycle. It turns out that our body even undergoes a complete replacement of the skeleton, which takes about 10 years. However, some organs do not fully regenerate. According to the researcher, during our lifetime we are able to replace only 40% of all cardiomyocytes (cells responsible for the contraction of the heart muscle). The process of cell renewal in our brains may be even slower. Scientists have previously found evidence that some neurons in the hippocampus renew themselves at a rate of 1.75% per year.
And according to Bergman, most neurons stay with a person for life, so we don’t have to worry about personality changes. And this raises a legitimate question: if the cells in our bodies are constantly renewing themselves, with rare exceptions, what prevents us from staying young forever? Or at least from living very, very long?
The thing is that here, according to Bergman’s words, there is such a concept as biological age. The cells of your organs may be new, but they are not the same as they were 10 or 20 years ago, because as a result of the constant copying and division of DNA, there are inevitable errors and mistakes that tend to accumulate over time, as in the case of numerous rewrites, and this cumulative effect leads to the fact that, for example, your liver will still be completely renewed every three years or so, but it will still be a new old liver.