Microscopic reinforcements
All the microorganisms in and on your body are part of an ecosystem known as the human microbiome, or human microbiota. In total, you have more than 100 trillion microbes – mostly bacteria, but also many fungi, viruses and archaea. They’re involved in many important processes, and they help you stay healthy. Microbes live on almost every surface, and in every opening, of your body. They form diverse and interesting communities, especially in your intestines, skin, nasal cavity and airways, mouth and genitals.
Extra organ
The importance of benign microbes in your body has only truly been recognised since the late 1990s. Before then, bacteria were mostly seen as pathogens, and they were unceremoniously attacked with antibiotics. But now, we know better. The microbiome is often even seen as a sort of ‘extra organ’. The important tasks of your body’s own microorganisms can be compared to those of your liver, heart or kidneys. For example, your intestinal bacteria ensure a much more efficient metabolism. They also make important nutrients, such as vitamins.
Intestinal bacteria in your colon.
Repel and tolerate
The body is in constant contact with microbes, both harmless and harmful. Your good microbes help you defend against the bad microorganisms from the outside world. They do this by, for example, out-competing pathogens in number. But they also ‘train’ your immune system. Good microbes ‘teach’ your immune system to weed out those few pathogens, and yet leave alone those billions of harmless microbes. That means that our immune system not only plays a role in fighting infections, but also is very important in our tolerance of helpful microorganisms.
Border guards
Your body’s own microbes are located primarily on your skin, on your genitals, and in the mucous membranes in your nose, lungs, oesophagus, stomach and intestines. So, actually, in all the places in which your body comes into contact with the ‘outside world’. In that sense, the exterior of your body is made up of mucous membranes, in addition to skin. This exterior protects the interior. The blood, brains, and most organs are, under normal circumstances, therefore virtually microbe-free.
Tennis court
Together, the skin and mucous membranes cover a huge surface area. The skin of an adult man has the same surface area as a single bed: around 1.8 m2. The mucous membrane of the large intestine comprises around 5 m2, about the size of the average bathroom. The small intestine takes the cake with a surface area the size of a tennis court (200 m2). This is mainly due to the presence of an enormous number of finger-like protrusions, called villi.
Because of the jobs they do, like the exchange of gasses (in the lungs) and nutrients (in the intestines), mucous membranes are easy to penetrate. So microbes can penetrate, too. That’s why mucous membranes are quite susceptible to infection by harmful microorganisms. To protect and reinforce the mucous membranes, mucosal cells produce a thin layer of mucous.