[gecko5]

I remember reading somewhere that every 7years the human body replaces every cell.
Essentially, nothing exists of you, that existed 7years ago. What about the thousands of
Eggs females are born with?

[Thomas1970]

Hi Gecko,
Of course, cells are being replaced in the body constantly, and to the best of my knowledge, if I remember correctly, this estimate is about right. Though cells are most commonly replaced or recycled due to damage, or normal wear leading to an inability to perform their vital functions, as in the case of worn red blood cells.
Human eggs or "oocytes" aren't necessarily subject to many of these same conditions.
Here is a good link explaining the duration of human fertility:

http://www.newton.dep.anl.gov/askasc.../mole00332.htm

[gecko5]

Let me ask the question in a different way. On a 50yr old man or woman, are there
Any cells 50years old. Brain,spinal cord, cornea? Thank you for your help.

[sovaira]

“People tend to think that old tissues have less regenerative capacity because they are wearing out,” said Sean J. Morrison, a Howard Hughes Medical Institute investigator at the University of Michigan who led the study of the switch's role in the brain. “This work shows that they are not just wearing out; they are actively shutting themselves down".

Well I think that all the cells are replaced after a particular period but all cells do not wear out or get replaced at the same time. They all have different rates and we can say different half life,if I explain in an easier way.

You see the neuronal cells do not regenerate themselves although they can repair themselves to some extent.but I don't agree that we are the new we ,after every 7 years,you the epithelial cells of skin are repalced after this period ,so this may be misleading in a way.


Well that was a good question, and if some one else explains it a better way ,it will add up to our information.