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.