Re: In older persons, does cell differentiation ever cease?

Nothing REALLY certain is known about the human aging process, as of now. 

However, there are certain theories, which try to explain WHY we age and 
HOW it is done. 

Certainly, CELL DIFFERENTIATION plays an important role to the scheme of 
discovering the exact ways HOW we age. And because the mechanisms of Cell 
Differentiation have been extensively studied, scientist try to find the 
mechanisms of AGING among the mechanisms of cell differentiation. 

But now to give you an exact answer to your question:

Of course Cell Differentiation ceases in old persons, some times. And that 
is when they DIE... ;-) Alright, that was some black humor, so let me try 
to put it into some other words.

In older persons CELL DIFFERENTIATION slows down, which is based on 
biochemical pathways that do not function as efficiently as they used to 
when these people were young. Some crucial CELLS might not proliferate 
sufficently and thus the surrounding tissue is hindered in its proper 
development. For example, that's the reason wounds of old people take 
longer to heal than in younger persons. 

But in oder to completely STOP CELL DIFFERENTIATION a cell has to receive 
SPECIFIC BIOCHEMICAL signals. Once they received those signals they move 
into the "S phase". That means they no longer undergo mitosis and will not 
yield ANY replicas of itself. Normally this happens after the usual time of 
usage of a normal cells ~100 days. After a while these cells die off 
through Apoptosis. 


But there is no reason why cell differentation should ever cease completely 
in older people. Sure it is slowed down (see: Telomere/Telomerase 
Hypothesis) but only some cells cease their differentiation due to the 
signals they receive. 

I hope that this will give you some insight into the matter of AGING. 

But believe me: Once you EXPERIENCE "AGING" you'll be glad NOT to know so 
much of it... ;-)