[lolaryan (OP)]

Hi, I have just listened to the podcast on stem cells and I am wondering where this all fits in with normal cell division. Do differentiated cells divide when they get to a certain size or are they produced by stem cells dividing?



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[chris]

Interesting question. The role of stem cells is to replace mature senescent cells. For instance red blood cells last about 120 days before they wear out and the body breaks them down and recycles the contents. This means that about 10^11 cells are being broken down and need to be replaced every day.

To achieve this, red cell progenitors (stem cells) in the bone marrow divide at the right rate to produce fresh cells. If you need more cells for some reason, such as living at altitude or if you've suffered a haemorrhage, then the stem cells increase their rate of division.

When the divide a single cell splits by mitosis to produce two daughter cells. One remains behind as a stem cell whilst the other leaves to become a mature cell type. Exactly how this cell fate decision is made (who is going to be the stem cell and who is going to be the progeny) isn't clearly understood yet.

I hope that help

Chris