According to this source... http://www.madsci.org/posts/archives/2001-02/981770369.An.r.html" [Broken] ...there's 28.8 kg of hard tissue per 70 kg adult human, made up of ~4 trillion cells. There's 31 trillion blood and related non-tissue cells, thus a grand total of 35 trillion human cells, and there's ~40 trillion bacteria in the colon. Thus the average tissue cell masses ~7.2E-12 kg and so contains ~688 trillion atoms at an average atomic mass of 6.3. If you exclude the 10% hydrogen, the average atomic mass is 15, so there's ~260 trillion non-hydrogen atoms per cell.To answer the original question, there's 6.72E+27 atoms in 70 kg of human, of which 2.54E+27 are not hydrogen. Thus in 35 trillion cells there's an average of ~192 trllion atoms per cell, ignoring the bacteria that mostly live in the gut and don't mass too much.
There seems to be a lot of non-cellular material in the body, mostly water in all likelihood.
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