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How many human cells are there in our body, on average?

How many human cells are there in our body, on average?


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How many human cells are there in our body, on average?

Wikipedia says 1013:

Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in the body (approximately 1014 versus 1013).

The Nobel site says 1014:

An adult human being has approximately 100 000 billion cells, all originating from a single cell, the fertilized egg cell.

The Physics fact book insists it's 1013:

(length of 1 bp)(number of bp per cell)(number of cells in the body)
(0.34 × 10-9 m)(6 × 109)(1013)

Finally, Wolfram Alpha gives 1.0 × 1014 as fact:

Estimated number of eukaryotic (human) cells in the human body: 1.0×1014

I am quite confused: who is right here?


Bianconi et al. 2013 give an estimated lower bound of 3.72 × 10^13 (which, by the way, is approximately the geometric mean of 10^13 and 10^14).

However, from the table in their Supplemental Information (where estimates for about fifty different types of cells are added up), it is clear that the vast majority of these are the erythrocytes, also known as red blood cells: estimated at 2.63 × 10^13. While the second largest class are the glial cells (from the nervous system), estimated at 0.30 × 10^13. Three other classes (endothelial cells {vessels}, dermal fibroblasts {skin}, and platelets {blood}) add up to another 0.58 × 10^13. These, in total, is about 3.5 × 10^13, and we can stop there, because the uncertainty in all these estimates swamps all the other cell type populations, which are much smaller.

This means that if we only consider the 5 most abundant cell types in the body, we already get a very good estimate. Is it likely that we have missed a cell type of which there are a trillion cells in the body? It's not impossible, but unlikely, because it would be hard to miss all these cells.

Maybe there is a long tail (i.e. a large number of minor cell types, each with a small, but significant population) that wasn't considered? Together, these could add up to a significant adjustment to the above figure. I don't know.

This estimate is for a typical human person: 30 year old young adult, 70 kg, 1.72 m tall and with a surface area of 1.85 m^2. For this person, the figure is given with roughly a +-20% uncertainty.

Given all the above, it's probably safe to say "30 to 50 trillion".

(This obviously doesn't take into account any of the bacteria mentioned above.)


In Mike Lynch's "The Origins of Genome Architecture", he claims 10^13. I forget the primary source he cited, and since the book is in my office I can't check it now.

** Found the snippet that contained the reference. I think it's really worth including in its entirety.

A crude estimate of the amount of DNA within currently living organisms can be made by noting that the length spanned by one base of DNA is ~0.3x10^-12 km (Cook 2001).

The number of viral particles in the open oceans is ~10^30 (Suttle 2005). Assuming that there are twice as many viruses on land and in fresh water does not change the global estimate very much at the order-of-magnitude level. Thus, assuming an average viral genome size of 10^4 bp, the total length of viral DNA if all chromosomes were linearized and placed end to end is ~10^22 km.

The estimated global number of prokaryotic cells is ~10^30 (Whitman et al. 1998), and assuming an average prokaryotic genome size of 3x10^6 bp yields an estimated total DNA length of 10^24 km.

With a total population size of 6x10^9 individuals, 10^13 cells per individual (Baserga 1985), and a diploid genome size of 6x10^9 bp, the amount of DNA occupied by the human population is ~10^20 km. Assuming there are ~10^7 species of eukaryotes on Earth (~6 times the number that have actually been identified), that the average eukaryotic genome size is ~1% of humans, and that all species occupy approximately the same amount of total biomass, total eukaryotic DNA is ~10^5 times that for humans, or ~10^25 km.

Given the very approximate nature of these calculations, any one of these estimates could be off by one or two orders of magnitude, but it is difficult to escape the conclusion that the total amount of DNA in living organisms is on the order of 10^25 km, which is equivalent to a distance of 10^12 light years, or 10 times the diameter of the known universe.


The human body has about 37 trillion cells, comprising 200 different types. Each cell has structures responsible for making 100,000’s of different proteins from 20 types of amino acids. Despite this, the code to produce all of these cells and much more is stored in the DNA of (almost) every cell, and all cells come from the same cell.

Each of the 200 different types of cells has a unique function, but most produce proteins that perform many of a given person’s bodily functions.

  • Humans have about 37.2 trillion cells. [1]
  • There are 200 different types of cells. Within these cells, there are about 20 different types of structures or organelles (organs within a cell). Each organelle performs a different function. [1]
  • During a human’s lifetime, many cells will replace themselves every 7 – 15 years, but not all cells do this. Some replace themselves every few days or weeks others never replace themselves.

TIP: See a List of distinct cell types in the adult human body for more information on cell types and functions.


Different types of cells have different lifespans, e.g.:

  • we shed our skin cells about every 35 days

  • red blood cells live about 120 days, platelets 6 days and white cells less than a day

  • most of the adult skeleton is replaced about every 10 years

  • the average age of a fat cell seems to be about 10 years

  • a 25-year-old heart replaces about 1% of all its cardiomyocytes (heart muscle cells ) over the course of a year, while a 75-year-old heart replaces about half a percent

  • our neocortical neurons, the cell type that mediates much of our cognition, are produced prenatally and retained for our entire lifespan

I want to throw in a philosophical side note and quote computer scientist Steve Grand:

"Think of an experience from your childhood. Something you remember clearly, something you can see, feel, maybe even smell, as if you were really there. After all, you really were there at the time, weren’t you? How else would you remember it?

But here is the bombshell: you weren’t there.

Not a single atom that is in your body today was there when that event took place … Matter flows from place to place and momentarily comes together to be you.

Whatever you are, therefore, you are not the stuff of which you are made.

If that doesn’t make the hair stand up on the back of your neck, read it again until it does, because it is important."

[Richard Dawkins uses this quote in his TED Talk (around 10:20)]


Here's How Many Cells in Your Body Aren't Actually Human

If you've ever read anything about the colonies of bacteria that live on and inside you, you'll no doubt have come across the neat little 'fact' that microbial cells outnumber human cells in your body by a ratio of around 10:1.

You'll find it in scientific papers, magazine articles, TED talks, and popular science books, and while it does a good job at illustrating just how crucial bacteria are to the existence of human beings, it isn't actually true.

In 2016, a review of more than four decades of research into the human microbiome found that there is zero scientific evidence to back this oft-cited factoid up.

Instead, the ratio looks to be about 1.3-to-1, with the average human playing host to around 100 trillion microbes, give or take. But even that isn't the whole story.

To figure out the true number, a team of biologists led by Ron Milo from the Weizmann Institute of Science set out to review all the available literature on the microbe populations that live inside us.

They found that for a man between 20 and 30 years old, with a weight of about 70 kg (154 pounds) and a height of 170 cm (about 5'7) - they call him the 'reference man' - there would be about 39 trillion bacterial cells living among 30 trillion human cells.

This gives us a ratio of about 1.3:1 - almost equal parts human to microbe.

So where did the 10:1 ratio come from, and why did Milo and team have to be so specific about the particulars of a 'reference man', instead of just coming up with a ratio for the plain old average human?

The origin of the 10:1 ratio has been traced to a paper published in 1970 by American microbiologist Thomas D. Luckey, who estimated that there are 100 billion microbes in a gram of human intestinal fluid or faeces.

Because there are about 1,000 grams of these materials in the average adult, he said, that equals a total of 100 trillion microbes. (Bear in mind, that every single one of these figures has no backing in scientific evidence whatsoever, as Ed Yong has noted over at The Atlantic.)

Seven years later, well-known microbiologist Dwayne Savage took this vague estimate, mashed it up with the fact that there are about 10 trillion human cells in the average human, and came up with the 10:1 ratio.

Everyone, from fellow scientists to the public alike, took that factoid and ran with it, and it wasn't until 2014 that someone made an effort to fact-check it.

Judah L. Rosner, a molecular biologist and geneticist from the National Institutes of Health, wrote a letter to Microbe Magazine insisting that more recent estimates for human cell numbers were nowhere near 10 trillion.

In fact, coming up with a cell count for the average human would be basically impossible, as Ed Yong explains:

"More recent estimates, he noted, put the total number of human cells at anywhere from 15 trillion to 724 trillion, and the number of gut microbes at anywhere between 30 trillion and 400 trillion. Which gives a ratio that can best be expressed as ¯\_(ツ)_/¯."

This is where the reference man comes in - narrowing down the sex, age, weight, and height of a hypothetical human made it a whole lot easier for the reviewers to figure out what the average number of human cells would be.

For their reference man, it's about 30 trillion, the researchers estimate.

On top of that, Milo and his team also discovered that microbe cell counts in the colon - where Luckey got his original figure from - have regularly been overestimated in the scientific literature.

"[W]hen previous studies made their estimates, they used the density of bacteria per gram of 'wet content' of the colon, times the volume of the entire alimentary canal," Lindsey Kratochwill has noted at Popular Science.

"But, these researchers argue, the bacteria density of the colon is much higher than the rest of the tract, so assuming that the entire alimentary canal is as bacteria-filled as the colon is would be overkill."

Accounting for this, and the fact that we have a far higher concentration of bacteria in our guts than in other organs and body parts (which means you can't take a sample from the colon and say it's representative of the entire body a la Luckey), Milo's team came up with an updated and more scientifically accurate estimate of 39 trillion microbial cells, based on the available evidence.

But even that 1.3:1 ratio - 39 trillion microbial cells to 30 trillion cells - isn't really something we should be citing in our textbooks and scientific papers going forward, as Ed Yong argues.

"These new estimates might be the best we currently have, but the studies and figures that Milo amassed come with their own biases and uncertainties," he says.

"My preference would be to avoid mentioning any ratio at all - you don't need to it convey the importance of the microbiome."


How many human cells are there in our body, on average? - Biology

I'm sorry that I have taken so long to answer your question, but it VERY specific, and I wanted to try to figure out the best answer that I could.

First of all, lets take a look at the scope of your question. To start, we have to think about how many cells we have to start with. Our bodies are made of cells of course, but no one has been able to sit down and count each and every cell to see exactly how many go into making a person. We have to make estimates based on the size and distribution of the different types of cells, and the mass of an adult human body (in this case, the adult male body). These estimates lead us to conclude that, each of us has on the order of seventy-five to one hundred trillion cells that make up their body.

However, not all of those cells are what you would call, 'human' cells (i.e. cells that contain your own genetic material). About 40 trillion of your cells (comprising almost 50% of your body's cell count) are bacterial cells that live in your digestive system, primarily in your large intestine. However, these bacterial cells are much smaller than the cells that make up your body, so more of them can fit in a small space.

50% of your body's cell count, only about 10% (or

4 trillion cells) make up the solid tissues that we think of when we think of the human body (muscles, spleen, kidneys, bones, brain, stomach, skin, etc.). The remaining 45% percent of the cells in your body are blood or lymph cells of some sort that are not associated with any solid tissue. These cells actually comprise most of the cells in your body. There are approximately 30 trillion Red Blood Cells, 2 trillion Platelets, and 500 million White Blood Cells in your Circulatory System. In your Lymph system there are about another trillion lymphocytes and immune related cells. That makes a total of about 38-40 trillion cells. Naturally, most of the MASS in your body is comprised by the 4 trillion cells that make up your solid tissues, especially your muscle and skeletal cells.

Now, the process of staying alive is a constant balance between losing cells and making more cells to take their place. When we are young and growing, we are making many more new cells than we lose existing cells, and when we reach really advanced ages, or when we get sick and start to die, we are losing more cells than we are making new cells to replace them. Because every person is different, and because we are all at different ages, it seems like it would be difficult to determine how many cells we lose every second, because there is no such thing as a model or average person. However, I am willing to try and make an estimate, as long as you realize that it is a very rough approximation.

First of all, I think I will focus only on those cells in your body which are your own. That means that I won't count the 40 trillion bacterial cells that live in body. However, as you note above, most of the cells in your body are Red Blood Cells (aka Erythrocytes, or just RBCs). There are about 30 trillion of these, and we know that they have a lifespan of only 120 days. That means that every 120 days, your body has gone through 30 trillion RBCs. That doesn't mean that all 30 trillion of them are made at the same time, or that they all die at the same time, but at any given time you can be certain that all of the RBCs you had 4 months ago are gone.

So, in 120 days, there are about 10.4 million seconds (10,368,000 to be exact). That means that in any given second, 30 trillion / 10.4 million or 2.89 million RBCs die. So, our estimate for RBCs is about 3 million cells lost per second, or less than the number of RBCs found in one cubic millimeter (aka one microliter) or blood.

Since most of your other cells (the cells in your solid organs) don't turn over that rapidly, the actual rate of loss will probably not be much higher than that when you consider it over the entire healthy portion of your life.

We can calculate a low estimate by thinking about the issue in an entirely different manner. The atoms in your body go through a complete turnover about once every seven years. As with the loss of RBCs, this does not mean that your body is rebuilt miraculously on your 7th, 14th, 21s, 28th, etc. birthdays. Rather at any given time, most if not all the atoms that were in your body seven years ago will have been lost through metabolic turnover. So, if you consider that replacement of all of the atoms in a cell to be the 'loss' of a cell (a loose definition at best), then in any given second you are lose

40 trillion / (7 * 32 million) or 181,000 cells on average.

So, to answer your question, the number of cells that an adult male human loses per second is somewhere between 200,000 and 3,000,000 cells per second, and is probably closer to 3,000,000. Still since these are very rough average estimates, and since the difference between 200,000 and 3,000,000 is only one order of magnitude (one factor of 10 times), so you would be safe saying anywhere around 1,000,000 cells per second. When you consider that you have 40-50 trillion of your own cells in your body, that means that on average one cell out of every 40-50 million or more dies each second. Considering it that way, it doesn't seem like that much at all.

If you want to know more about where the estimated numbers for the number of cells in a body comes from, check out Chapter Eight of the Nanomedicine web site. This is an online version of Nanomedicine by Robert Freitas.

For information about Red Blood Cell turnover, take a look at this Red and White Blood Cell page on the Virtual Hospital web site.


How many bacteria vs human cells are in the body?

When people ask me what the microbiome is, part of my answer usually includes the fact that there are 10 times as many bacteria in the body as human cells in the body. Unfortunately, I may no longer be able to use that statistic. A recent study out of the Weizmann Institute in Israel states that the number of bacteria may actually be very similar to the number of human cells in the body.

The authors of the study found that the 10:1 ratio of bacterial to human cells goes back to a 1977 study by Dwayne Savage and an earlier 1972 paper estimating the number of bacterial cells in the human body. The Weizmann scientists redid the estimate and found that there were about 39 trillion bacterial cells in the body. They also estimated the number of human cells in the body, about 84% of which are red blood cells, finding there to be about 30 trillion human cells in the body.

While this results in about 1.3 bacterial cell per human cell, the numbers may vary significantly from person to person and could change significantly with each defecation. They estimate that the range of bacterial cells goes from about 30 to 50 trillion in each individual. Women may also have a higher ratio of bacterial cells than human cells because they have fewer human cells, specifically red blood cells.

While this study does not take into account fungi, viruses, and archaea which all make up the human microbiome and would increase the ratio of microbes to human cells, the often stated ratio of 10:1 for bacterial cells to human cells is most likely not accurate. While I will no longer be able to use this fun fact in my description of the microbiome, it does not take away from the importance of bacterial cells in human health.

Please email [email protected] for any comments, news, or ideas for new blog posts.

The views expressed in the blog are solely those of the author of the blog and not necessarily the American Microbiome Institute or any of our scientists, sponsors, donors, or affiliates.

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What is the life span of lung cells? anon961228 July 15, 2014

@Hamje32: It's called telomeres. Specifically, telomere shortening as we age. I don't understand it much, but apparently it's what makes these cells and tissues eventually wear out. anon350835 October 8, 2013

Your chromosomes (DNA) grow shorter every time your cells split. this goes on to a point that your chromosomes are to short and no new cells can be made. Your cells need DNA, because it tells the body how to work. of course eating healthy helps the cells have proper nutrients and last longer, but in the end you will die.

If humans ever find a way to stop chromosomes from growing or making cells stronger to live longer, we could become immortal. anon330652 April 17, 2013

We wrinkle because of the sun. We die because years and years cells change us. Our DNA tells us when we die. anon324023 March 7, 2013

I had pre-cancerous cells on the roof of my mouth. What is the chance of this coming back? miriam98 July 17, 2011

@hamje32 - There’s something called Life Cell that claims to address the wrinkle problem, but I haven’t tried it anymore than I’ve tried any of the other anti-wrinkle, anti-aging products. I prefer to age gracefully.

I do think that you raise a good point I don’t think that there’s any real reason why cells can’t generate for a much longer life span than they do.

I’m on a kind of partial vegetarian diet, and the promoters of this diet have been saying for years that fruits and vegetables do a better job of helping cells stay young and rejuvenated than does a diet of meat and potatoes. I don’t know if that’s totally true, but I do know that I feel better on the partial vegetarian diet. hamje32 July 16, 2011

This is fascinating, and raises an obvious question. If human cells live and die and regenerate themselves, why don’t we live forever? Why do we age and get wrinkled and go to our grave? Is it really the grim reaper that calls us away?

I realize that there are scientific answers to these questions, but I am asking them more or less hypothetically. I believe that medical science will continue to improve so that cells can be regenerated for a much longer time span.

I don’t think we’ll ever live forever, but since we know that nature is busily regenerating cells on her own, at least we can help her out and expect longer life spans. Perhaps well find something akin to the fountain of youth for our wrinkles too.


Bones

The largest bone in the body is the femur, or thigh bone it is 20 inches long in a 6-foot-tall person.

Main job: To give shape to your body.

How many: At birth you had more than 300 bones in your body. As an adult you'll have 206, because some fuse together.

The smallest bone is the stirrup bone, in the ear it is .1 inch long.

Kinds of Bones

  • Long bones are thin they are found in your legs, arms, and fingers.
  • Short bones are wide and chunky they are found in your feet and wrists.
  • Flat bones are flat and smooth, like your ribs and shoulder blades.
  • Irregular bones, like the three bones in your inner ear and the vertebrae in your spine, come in many different shapes.

How much DNA is in a human being?

A single copy of the human genome contains around 3,234.83 Mb, or 3,234,830,000 individual bases. However, almost every cell in a human body contains two copies of this genome (one maternal and one paternal), giving to 6,496,660,000 bases per cell. Although it is divided into 46 separate chromosomes, this corresponds to roughly two metres and fourteen centimetres of DNA per cell, although it would weigh only

To work out how much DNA is in the whole body, we’ll need to know how many cells a body has. This is the most difficult aspect of this question, as it’s as yet impossible to count. Estimates have ranged from 5 billion to 200 million trillion. However, a very thorough paper in 2013 attempted to measure the cell density of each tissue type (fat tissue, muscle tissue, etc.) and, knowing how much of each tissue type there is, extrapolate the number of cells from that. Their final answer was 37.2 trillion cells in an average adult male. Each of these will contain a full genome, with the exception of red blood cells. Red blood cells don’t actually contain any DNA at all, although this will barely impact the total amount of DNA, as there are “only” around 30 billion of them in the body.

So with 37.2 trillion cells, each containing 2.14 metres of DNA, this gives a total DNA length of 79,608,000,000,000 metres, or 79,608,000,000 kilometres. For reference, the moon is only 384,400 km away, and the sun 150,000,000 km away. This means that the DNA in your body would reach from the earth to the sun 530 times, although it would still weigh only 2.6 kg.


I'm 32. Is there a single cell, or even molecule, left in my body that was there when I was born or am I a completely physically different organism from who I was as an infant?

Have all original molecules in my body from birth been replaced by now or do some remain? If they've all been replaced, approximately how often does this occur in a human lifespan, rendering one a completely different physical being from who we once were aside from the ties of continuity?

There may be others, but on a molecular level I would say the enamel on your teeth teeth and cartilage on your bones. These are permanent structures that once formed, do not change (much) unless damaged somehow.

If you are talking about the cellular level however, then you can encompass a much wider range of tissue, because while the individual molecules that made up the cells may be long gone, they are constantly being replaced by new ones such that the structure of the cell is effectively the same one you have always had. This can be said of many (not all) of your nervous system cells, heart cells, and bone cells.

EDIT: As far as the replacement rate goes, it varies a lot depending on tissue. Skin may be the fastest, replacing itself within a month. Full red blood cells turnover takes 4 months. Some (like the ones above) never fully turnover. I believe the heart on average turns over 40% of its cells in your lifetime. These rates tend to reflect the function of the particular tissue.

EDIT2: Forgot GI epithelial cells, they are the fastest, replacing themselves in days.