|MadSci Network: Cell Biology|
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... ;-)
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