Another myth about the human body busted…

Another myth about the human body busted…

For years we have been thinking that we are only 10% human, as our own cells were reportedly greatly outnumbered by bacteria. However, newer calculations suggest we are likely 50% human – and that actually “each defecation event may flip the ratio to favour human cells over bacteria”.

How comes we have been wrong about such an important thing for such a long time?

It is in fact quite difficult to establish reliable numbers for the bacterial load in our body.  A particular overestimate in the early works relates to the proportion of bacteria in our gut. The study on which most subsequent calculations were based estimated that our intestines contain around 1014 bacteria, by assuming that there were 1011 bacteria in a gram of faeces, and scaling that up by the one-litre volume of the alimentary tract. But among the sections of the alimentary tract only the colon contains high numbers of bacteria. The new reviewed data indicate that there are about 2.5 times less bacteria than stated in early work (and re-re-re-cited many times).

Another uncertainty factor is indeed also the number of human cells in the body. The updated calculations suggest that there are about 3 times more human cells than suggested by previous calculations. As cell types vary greatly in size and density, we cannot simply extrapolate from cells found in blood to the various other cell types found in the body. Most of our cells are red blood cells, while fat and muscle cells account for only 0.1% of cells but 75% of our body mass.

“Should we care about the absolute number of human cells in the body or the ratio of bacterial to human cells?”

Updating the ratio of bacteria to human cells from 10:1 to 1:1 does not take away from the biological importance of our microbiota. The new numbers will not revolutionize our way of thinking about the human body, or not tremendously bring forward our current research. Rather, we can agree with the authors of the study, saying that “In performing these kinds of calculations, we become intimately familiar with the limits of our current understanding”.
Reference: Sender, R., Fuchs, S. & Milo, R. http://dx.doi.org/10.1101/036103 (2015)

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The human gut surface – the size of a tennis lawn* ?

The human gut surface – the size of a tennis lawn* ?

*for non-tennis-aficionados: a tennis court is about 195.6m² (for single matches) – I looked it up…

Your biology class textbook from back in the days probably stated that the human gut surface area is the size of a tennis court, and popular science articles still hold on to this illustrative comparison.
However, newer calculations provide updated data on the surface area of the human gut – and it is indeed smaller than a tennis court. It averages about 32m² to be more precise. Still pretty big for something that looks like a simple tube hidden in our body. The gut surface is tremendously increased by numerous villi and microvilli, small folds that line the inside of this tube. And we just take it for granted that all that surface gets properly maintened to keep on functioning well.

A large gut surface to nourish the whole body

Why is it in the first place that our gut has this large surface area? The gut’s foremost task is to digest food and take up all the nutrients, providing energy (from carbohydrates, proteins, fat and alcohol) as well as necessary building blocks our body cannot produce itself (such as amino acids and most vitamins). Our body is designed in a way that allows to extract and take up as much enery as possible out of the food, and a larger surface allows for a more efficient uptake. Historically this was essential for survival. Nowadays pharmaceutical companies in their efforts to find a weapon against obesity try to trick the body into NOT doing so (you can find an example here).

The gut surface – a continous front line

While facilitating the uptake of nutrients, this huge surface area calls for a lot of maintenance work. Our gut is inhabited by a plethora of bacteria, called our microbiota.
On the one hand, the microbiota is beneficial, helping to further break down food components we cannot digest and thereby providing more energy for us. It also provides a front-line defense against pathogens such as Salmonella and E.coli.
On the other hand, these bacteria need to be kept at bay at all times. This means our immune system needs to prevent them from growing too much as well as from entering the body. And the more surface, the higher the chance that something goes wrong at one area in the gut, and bacteria can enter.

A lot of lawn keeping

In general, our immune system is programmed to fight everything that does not belong to our body. However, in the gut, it is constantly challenged by the microbiota. So in order to not have a constant ongoing inflammation in our gut, our immune system is able to recognize our microbiota as innocuous and dampen the reaction towards it. This is not an easy task. And also, it not always works out perfectly: Inflammatory bowel diseases (IBD) such as Ulcerative Colitis and Crohn’s disease are results of a disturbance in this process. A variety of immune cell types need to communicate in order to maintain what is called a “gut homeostasis” – a healthy gut that is not overreacting to its microbiota.

The infantry, the strategy and what goes wrong in IBD – you can read more about these in the future articles.

Reference: Helander H.F. & Fändriks L., doi: 10.3109/00365521.2014.898326.

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Pathology – behind the scenes…

the Norwegian version is now published on Forskning.no
the English version is now published on Science Nordic


Pathology – behind the scenes…

Upon telling people that I work in the Department of Pathology, I can often tell what they think – they imagine me all dressed in white, performing autopsies on dead bodies and reporting back to police force about the cause of death, CSI-style…
In fact, I’m rarely dressed in white and – Thank God – I don’t get to see many dead bodies. So, what do I do then?

Pathology – the true story

Pathology is a branch of medical science primarily concerning the examination of organs, tissues, and bodily fluids in order to make a diagnosis of disease. Even though this is a citation from Wikipedia, it is still true. The discipline that gives rise to CSI’s superstars (and they are not realistic, just a side note…) is called Forensic Medicine, and that is not the same as Pathology.

Two types of “Pathologists”

Pathologists at the hospital do perform autopsies, but they mostly look at biopsies or a smear of body fluids, such as blood, from patients. Their aim is to make a correct diagnosis. They identify and characterize diseases such as cancer or inflammatory disorders. By studying the cells in detail, the pathologists cooperate with the clinicians in their diagnostic work. For example, the pathologist’s examination and classification of tumor cells is an important factor that helps the clinicians decide on the treatment that this particular cancer patient will receive.

And it gets more complicated. Behind the scenes, basic researchers in the field of pathology try to figure out mechanisms of how diseases develop in the first place. I am one of them. We want to know what drives diseases, and what parameters we can use to define and diagnose and monitor them better. And finally we want to find out how they could be treated.

To understand the disease you need to understand “health”

In order to be able to accomplish all this, we need to know when we are looking at a disease. This, however, means that we first have to define what a healthy state is. We need to understand how the healthy state is maintained, and which components play critical roles in balancing out any disturbances.

Having a background in nutritional science, I am particularly interested in organs of the digestive tract. However, once we have figured out a basic principle for a particular organ, we can try to see if the findings hold true for other organs.
I look at pieces of more or less healthy gut tissue from (mostly alive!) people, and try to define what I see. In principle, I ask four types of questions: What cells are there? What function might they have? Do they change in cases of disease? What role might they play in keeping us healthy?

Answering these questions is the prerequisite for everything we try to find out about diseases, including the development of treatment strategies.

Not so bad, I think.

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Another research blog?

Another research blog?

Research blogs have become popular. Very popular.
The probably most popular site, IFLScience (‘I f*** love science’) has 21 Million Likes on Facebook and 172.000 followers on twitter. What a scope!

These pages on my blog are not meant to focus on ‘engaging and thought-provoking science’, as IFLScience puts it. Instead, they are meant to provide some enlightenment. A little guidance in all the daily “scientific” background noise. And who should be able to provide such guidance if not the people who know stuff? It must be us researchers.

I want to update interested followers, whether with or without scientific background, on what is going on in my field. And I might as well add my scientific but likely subjective view on it.
And finally, I would like to use these pages to try to make my family and friends understand what I actually work with…

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