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Asked by anon-254201 on 12 May 2020.
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Clare Harwood answered on 12 May 2020:
Hi Leon,
Interesting question! I don’t think anybody could possibly know exactly how many cells there are each of our in the bodies, because we are all different from one another. But scientists think that the average person has about 30 TRILLION CELLS! There is thought to be about 200 different human cell types and these come in all different shapes and sizes. For example a neurone in the brain can general be quite long and have lots of branches whilst cells that carry oxygen in your blood (red blood cells) are very round and shaped like a donut.
When we say 30 trillion cells we are only talking about human cells, there are also lots of bacterial cells in our body. Scientists estimate that we have ten times as many bacteria cells as we do human cells in our body. You might have heard of bacterial cells being in our body when in lines , but most bacteria in our body are good bacteria that help our body work normally. For example there are lots of bacteria in our gut that help us digest our food.I hope this helps, let me know if you have any more questions about this!
Clare 🙂
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Zoe Ross answered on 12 May 2020:
Hi Leon! Clare has given a great answer to this question. The numbers of cells are mind blowing but also I think it is so cool that we have more microbial cells than human cells. Our bodies are walking ecosystems!
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Ana Cruz answered on 13 May 2020:
Hi Leon,
fabulous question. Clare has indeed given a great answer already. Only thing I would add is there are certain cells that can evolve to become other types of cells. For example a stem cell is what we call pluripotent, it can become lots of different cell types like a fat cell or a muscle cell when given certain cues. When its a full-grown muscle cell, for example, it cant go back! In the many steps along that path, it can become lots of different things! It’s fascinating. Also why stem cells are so important to study! -
Ailith Ewing answered on 13 May 2020:
Hi Leon,
Great answers already so I’m just going to add to Ana’s point, which is super interesting. We can now look at the patterns of how different genes are turned on and off in individual cells and apply statistics to this data to map the path that types of cells go through as they change from one type of cell to another! This helps us understand the decisions that the cell makes along the various steps of the path. Single-cell sequencing like this is a hot-topic in medical science right now! -
Roberta Migale answered on 13 May 2020:
Hi there Leon! Many scientists across the last decades have tried to have a good guess at how many cells we may have in our bodies and it is interesting to see that the guesses fall over a huge range, from 5 billion to 200 million trillion cells!
This until 2013 when a group of scientists from italy, greece, spain looked back at these guesses and tried to make a better one. The idea was “simple”. Each organ in the body will have a different shape, be either bigger or smaller, elongated or very tiny. So they thought, maybe better to try to guess how many cells are in each organ and then add all these numbers up! It’s almost like a mathematical problem. They assumed that the mean weight of a human cell is 1 nanogram (think how tiny: there are 1.000.000.000.000 nanograms in a kilogram!), and the mean volume is 4×10^(-9) cm3 (nevermind the number-is super small!). Since they knew the weight or each organ of an average man (30 years old adult, 70 kg of weight, 1.72m), this is how they then calculated how many cells are estimated to be present in each of its organs. And the number was…..37.2 trillion cells! This is what as of today is considered the best guess we have 🙂 -
Nina Rzechorzek answered on 13 May 2020:
Hi LeonLogsy – great Q and excellent evidence-based estimates given by others already. All I will add is that the 37 trillion cells you might have right at this second will not be exactly the same 37 trillion you have tomorrow. That’s because some cell types are continuously dying and being replaced by new ones – how quickly this ‘turnover’ happens depends on the cell type.
One source suggests that fat cells are replaced at about 10 per cent per year, but heart muscle cells turn over at just 1 per cent per year at age 25, declining to 0.5 percent by age 70. Even if you live to be 100, you’ll still have more than half of the heart muscle cells you were born with. The neurones of the cerebral cortex and the cells in the lens of your eye are never normally replaced. But even though the cells aren’t completely replaced, they still change. Molecules are continually exchanged with the environment during ordinary metabolic processes. The water in your body turns over at about 3 litres per day. An adult has around 40 litres of body water, so that’s 7.5 per cent per day. After two years, it’s statistically unlikely that you have any of the same water molecules. But the calcium in your teeth is locked up forever. Nice summary video and webpage with more details below:
http://book.bionumbers.org/how-quickly-do-different-cells-in-the-body-replace-themselves/ -
Bilal Ahsan answered on 14 May 2020:
Awsome question and fantastic answers!
I would like to add that the height and weight of the human body varies and the total number of cells varies too. For instance, someone with 5 feet height and 50 kg weight would have fewer cells then 6.5 feet and 95 kg weight. However, the number still would be in trillions!
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