[thedoc (OP)]

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?
Asked by Kevin Hoover




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[thedoc (OP)]

We answered this question on the show...







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[img float=right]/forum/copies/RTEmagicC_Huw_n_01.jpg.jpg[/img] 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. 

So as you can see, there's quite a range in contrast of turnover rates of all the different cell types in the body.  And with regards to your question on what happens to the shed tissue, sometimes our cells are broken down into their components and recycled or if they're toxic, they can be packaged up for removal of a further processing, or they can be used up in the form of energy.

[CliffordK]

Hmmm.
The lens in your eye does not replicate, and gets stiff, and sometimes cloudy over time.  Thus the need for bifocals, and cataract surgeries.

I believe that the neurons also do not replicate, at least after a young age.

Obviously you get 2 sets of teeth.  However, I'm not sure to what extent tooth enamel is replaced, although dentists seem to indicate that it can replenish somewhat.

Most other cells in your body are slowly replaced.  Even bones are slowly remodeled (which allows repairs of both major breaks, as well as minor stresses).

[cheryl j]

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.

[imatfaal]

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.

As Cheryl says eggs in women.  I cannot remember the actual week - but every egg that a women will ever produce is already formed when she herself is still within the womb; which is a pretty awe-inspiring thought.  A woman pregnant with a daughter is not only carrying and nurturing the next generation but also the physical beginnings and genetic inheritance of her grandchildren.

[Satoyaki]

you are you. the real question is how much has been added.

[MelBrasil]

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.

So my question is: Only time modify us? How much the environment define us and our behavior? What is the essencial part that survive to these changes?