The human body has 36 trillion cells.

New research shows the number of cells in the bodies of adults and children, and assesses the relationship between cell number and size.

Nerve cells viewed under a microscope. Photo: Ed Reschke/Getty — Nerve cells viewed under a microscope. Photo: *Ed Reschke/Getty*

Cells are the building blocks of every tissue and organ in the body. The average adult male has about 36 trillion cells, an adult female has 28 trillion cells, and a 10-year-old child has about 17 trillion cells, according to a new study that looked at the size and number of 400 types of cells across 60 tissues, including immune, muscle, and nerve cells. The new study was published in the journal PNAS on September 18.

Scientists have previously estimated a similar number of cells — between 30 and 37 trillion — in adult men, but the relationship between cell size and number has not been studied at the whole-body scale.

"We were surprised to find a fairly consistent inverse relationship between cell size and number across the entire human body," said Ian Hatton, lead author of the study and a researcher at the Max Planck Institute for Mathematics in Science in Leipzig, Germany.

Thus, there is a “trade-off” between cell size and cell number. Larger cells have fewer total cells than smaller cells. This means that if cells are grouped by size, each group contributes an equal amount to the total body mass.

But the team also said the study had some limitations. For example, it focused on the “average” body size of adults and children. The study’s standard adult male weighed 70 kg, adult female weighed 60 kg, and child weighed 32 kg, based on reference figures from the International Commission on Radiological Protection (ICRP). This does not reflect the large differences in size and weight between different people.

In addition, the team said, there may be uncertainties in the data. In many cases, they had to rely on inferences about cell size made using microscopes and other indirect measurements rather than direct measurements. They also estimated total cell numbers in adult women and children based on studies that were conducted primarily on adult men, said team member Eric Galbraith, a professor at McGill University in Canada. “Unfortunately, there is still more information about men than women or children,” he said.

More research is needed to fill in these gaps, Hatton said. But he said the new study helps highlight some of the differences in cell counts seen in previous studies, which could have important health implications.

"Perhaps most importantly is our estimate of the total number of lymphocytes in humans, which play a vital role in immune function. We estimate that there are 2 trillion lymphocytes in the human body, four times higher than previous estimates. This could have important implications for diseases and health problems related to lymphocytes, such as HIV or leukemia," Hatton said.

Thu Thao (According to Live Science )

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