Jason Arunn Murugesu in New Scientist:
The average adult male has around 36 trillion cells in their body, while average adult females have 28 trillion, researchers have found. Unexpectedly, the mass of small cells in our bodies, such as blood cells, is roughly the same as that of large ones such as muscle cells – a finding that has puzzled researchers.
To count the number of cells in the human body, Ian Hatton at the Max Planck Institute for Mathematics in the Sciences in Leipzig, Germany and his colleagues analysed over 1500 scientific papers, looking at factors such how many cell types are there in the body, how many of each type are in each tissue and the average size and mass of each cell type. They found over 400 known cell types across 60 different tissues.
More here.