Kevin Hoover asked:
I am 57 years old. Do I have any original parts? In other words, how much of the baby that was born in 1954 is still part of me? Also, how much of the 18-year-old teenager that I once was is still with me? Do my soft tissues cycle out over time? What about bones, nerves and brain matter?
We posed this question to Kirsty Spalding, regeneration expert at the Karolinska Institute in Sweden...
Kirsty - For starters in the brain, most of your nerve cells that you're born with will be the ones that you have when you're older. Although we do continue to lose nerve cells as we age, there's very little areas in the brain that actually make new nerve cells in adulthood.
Also the lens capsule in the eye, this is also not turning over at all so the lens capsule will be as old as you are.
And with teeth, once we have our mature teeth, the enamel that's laid down in these teeth, this is not turned over at all.
Other organs in the body have much more dynamic turnover. An example of this is fat. We replace 50% of our fat cells per year. Other tissues, such as muscle, by the end of a relatively healthy lifespan of about 75 years, less than half of the muscle cells in the heart will have turned over.
Bone is a rather complex structure and in the middle, it has the bone marrow which is making the white and the red blood cells. Here, this is a highly proliferative area, such that millions of cells are being born per second.
I've heard different answers about the ability of brain cells and other nerve cells to divide and replace them selves. Bone growth stops in your teens and 20s. Bone remodeling is on going, but one anatomy book says at least part of the long bones like the femur may not be completely replaced in a lifetime. Heart muscle tissue is not replaced after maturity. I dont think other muscle tissue is either - it gets bigger by increasing the number of actin and myosin fibres inside cells. (When it is damaged, its replaced by scar tissue.) And teeth, as mentioned are original parts. Eggs in females.
you are you. the real question is how much has been added. Satoyaki, Sun, 19th Feb 2012
I think this question is very interesting. I am living in a place very different from the city where I was born. I m still in the same country, but everything is really different: culture, feeding, climate... so now I think how much of me still remained the same? I feel I had to adapt a lot to live here. Now I have other friends and I dress different clothes. My weekends are very different from the last 20 years, for example. I am feeling very strange sometimes, because I feel I am very different.