| Comments |
"During an average human life span, the cells inside the body cumulatively pass through approximately 10^16 growth-and-division cycles and, in the case of most of us, provide excellent health-something that we take for granted." "…the adult human body, for example, comprises almost 10^14 cells, and the organism as a whole undergoes as many as 10^16 cell divisions in a lifetime." "In fact, the cells in a mouse pass through about 10^11 mitoses in a mouse lifetime, while those in a human body pass through about 10^16 cell cycles in a human lifetime. These numbers, on their own, indicate the enormously increased risk of cancer development that is intrinsic to our biology relative to that of the mouse." A sanity check on this value relies on knowing that red blood cells are the dominant cell type by sheer number in the body (bacteria aside) and that their lifetime is on the order of 100 days. So in 100 years of life there will be about 300 cycles of red blood cells replacement and a total number of cell divisions is indeed of order 10^16 (taking into account we have about 3x10^13 cells in the body). (RM) |