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>"In mitotic tissues they will be replaced in the same way as any cell is replaced when it dies, by replication."

Replication from where though? The tissue stem cell that has already divided too many times?

From other somatic cells, and ultimately from the tissue stem cell population. That population is impacted by aging, as you point out. However, the effects of replacing 1% of tissues over some period of time are going to be negligible in comparison to the effects of having 1% senescent cells, given that those senescent cells and the inflammatory, harmful signaling they generate are one of the reasons why the stem cell population is less active, and regeneration less effective.

I guess no one knows for sure, but assuming errors accumulate after each cell division it'd make a lot of sense if, after some number of them, cell turnover slows and stops in order to avoid any further replication.

In that case your plan would be treating the symptom, not the cause (accumulated genetic errors and whatever other junk in the stem cells). I would also expect it to lead to cancer.

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