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On average, how many cells divide each day in a human being? How long does a cell wait before dividing itself ?

I have tried to look on the internet but surprisingly the answer is difficult to find..

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Thats pretty hard to answer, since the proliferation rate of cells is pretty different. For example heart cells hardly ever divide while cells of the hematopietic systems do this pretty often. –  Chris Feb 21 at 14:22

2 Answers 2

up vote 4 down vote accepted

My first thought was this:

According to Wikipedia (citation provided)

Between 50 and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day.

For every cell that dies a new one must be born, so there must be at least between 50 and 70 billion cell divisions to replenish these cells in an adult human (no net growth).

But then I remembered erythrocytes. Wikipedia again:

Adult humans have roughly 2–3 × 1013 (20–30 trillion) red blood cells at any given time, comprising approximately one quarter of the total human body cell number

and...

these cells live in blood circulation for about 100 to 120 days

So approximately 1% of erythrocytes are destroyed every day and must be replaced. That's 2-3 x 1011 cells formed every day, which dwarfs the cells replenished due to apoptosis (5 - 7 x 109).

Through this process [erythropoiesis] erythrocytes are continuously produced in the red bone marrow of large bones, at a rate of about 2 million per second in a healthy adult.

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100kg human = 1kg dna = 50g telomeres (where 100kgMice=1kgDNA=100gTelomeres), Human average telomeres are ~15KB, so we simply calculate 15000/100= 150bp = 1%, so we lose 1% of our telomeres per division. So humans' cells must have about 100 divisions per life time. Thus human Cells Divide on average (considering different tissue types differ in division rates, frequencies, etc): - twice a year. If thats the case, then all cells of humans are replaced over 50years or longer, or not at all, and just the old cells (with shortened telomeres) percentage is increasing till death cascades win totally. - Or Telomerase Doesnt twice a year (on average per life time). In a case, where telomerase has errors/etc , in which case, better telomerases (with less errors/etc) humans will live longer. And that would mean that the rate of new cells replacing old cells is less, but still around 3times/year/cell. But then why would over life time length increase. Thus this option is NOT the case! - Or each day, thus All Cells Die 3 times a Year, as if each cell divides every 24h. This would mean that we increase weight 3times a year, Or in other words, going through complete metamorphosis 3 times a year. This would mean that the overall rate of new cells changing old cells is 3 times/year/cell. But if thats was the case, then why would telomeres decrease with age. Thus this option is NOT the case!

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Can you please add some references for the claims/assumptions you make? This is especially necessary for the numbers... –  Chris Sep 9 at 14:58
    
The numbers are simple math A levels. The references are easy access wikipedia : ), e.g. the see for your self there, how much dna there is in a cell, then calculate : ) and dont forget to: Have fun : ) –  prof Sep 10 at 11:20

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