Question: How many times can cells reproduce?

Adam Paige answered on 21 Nov 2012:

That varies quite a lot depending upon which kind of cell in the body you are thinking about. Most of our body’s cells can divide a fair few times (maybe dozens of times). But each time they divide the ends of the chromosomes (called telomeres) shrink a bit. After a few dozen (maybe up to 100) divisions, the chromosome ends have been completely lost, the chromosomes start to break and fall apart, and the cell would not be able to divide any more and will die. This happens in cells of the liver or kidney for example.

Some cells in the body never divide. Cells in the brain and nerves, or the muscle cells of the heart. Once we are fully formed these cells never divide and therefore if we damage these cells they do not get repaired.

We also have some types of cells called adult stem cells. Stem cells are cells that can divide many, many times (maybe forever?) because they have a protein that repairs the chromosome ends and stops the chromosomes eroding and then breaking after many divisions. Stem cells divide to produce one cell which is a stem cell, and one cell which can change into a different cell type. So we have stem cells in our bone marrow that produce all the blood cells. And stem cells in our skin or intestines that make the epithelial cells of those tissues. These tissues containing adult stem cells are very good at making new cells (and do so all the time) and therefore are very good at repairing themselves when they are damaged.