From the oxygen-carrying blood cells in our blood to the branching neurons that control our thoughts, our bodies are made up of a dazzling array of cells.
Researchers from institutions in Germany, Canada, Spain and the United States have published a comprehensive study of how many individual cells of each type are in typical bodies.
Based on an exhaustive analysis of over 1,500 published sources, most adult males contain a total of about 36 trillion cells, while adult females tend to have about 28 trillion cells. A 10-year-old child, by comparison, would have about 17 trillion.
Beyond an overall cell count, the study revealed something really interesting: If you group cells into categories based on their size, each size category contributes roughly equally to the body’s mass.
“These patterns suggest an organism-wide trade-off between cell size and number and suggest the existence of cell size homeostasis across cell types.” the researchers write in their published paper.
To put it another way, there seems to be a natural balancing act in which fewer larger cells and more smaller cells are produced to keep the categories equal. What’s more, the variation in size in each category was also roughly equal.
Considering that the relative size of the body’s smallest cells (such as red blood cells) and largest cells (such as muscle fibers) is like comparing the size of a shrew to a blue whale, it’s a fascinating finding.
As the researchers point out, our cells are perfectly sized for their various roles – and any disruption to this scale often indicates the presence of disease. It is clearly important that this kind of cell regulation occurs, and it is done very cleverly.
Researchers have tried to estimate the number of cells in our bodies before, and the new figure is close to earlier, but what makes this latest study special is the way it also tries to dig into comparative cell sizes.
Future studies will have the opportunity to look at exactly how our bodies regulate the size and number of cells that make us who we are – and how this regulation works to keep our bodies healthy and growing normally.
The researchers hope that their results will be useful in many different studies of biology – and with that aim in mind, all data from the analysis are now available online.
“Our data serve to establish a holistic quantitative framework for the cells of the human body and highlight major patterns in cell biology,” the teams writes.
The research is published in PNAS.
