Microbiota. What is this organ and why do we need it

    The intestinal microbiota is the composition of bacteria that live in the human colon. Not so long ago, it turned out that these bacteria perform a number of important functions for the human body. Today, scientists call microbiota - a new body worthy of a separate study.

    The last time  Atlas and I wrote about oncology , and today we are launching a series of articles to better know what bacteria are, how they colonize our intestines and whether they can be controlled.


    Illustration by Rentonorama

    Where in our gut bacteria


    Bacteria inhabit everything around and inside us. They love a warm and humid environment. In the human body, most microorganisms are found in the mouth and intestines.

    Bacteria begin to populate our body when we are still in the womb. It used to be that the placenta and amniotic fluid were sterile, but recent studies show that this is not so. It is not yet clear how the bacteria enter the placenta, but there are suggestions that this is affected by the microflora of the vagina, bacteria in the oral cavity, which may enter the bloodstream in small amounts, and the intestinal microbiota, where immune cells (dendritic) select certain bacteria that penetrate the the placenta.



    However, large-scale colonization of the intestines with bacteria occurs during childbirth, breastfeeding and when the baby begins to eat solid food. By 1.5–3 years, a human microbiota profile is formed, which contains more than 1000 species of bacteria. Caesarean section, the use of antibiotics, an imbalance of bacteria in the intestines of the mother, premature birth, refusal to breastfeed are factors that negatively affect the formation of microbiota.

    Why exactly the intestines


    The task of the intestine is to absorb the maximum amount of nutrients, and this requires a large surface area. To fit it, the structure of the intestine is a tightly fitting folds with villi and microvilli. Because of this, the intestines are often compared to velvet tissue.


    Schematic structure of the large intestine

    The surface of the intestine is covered with a mucous layer - mucin. It protects the intestinal cells from aggressive representatives of the microbiota. Mucin is updated every hour, as part of this layer is taken away by fecal matter as it moves through the intestines.



    A moist, warm environment with a large number of folds and processes is an ideal environment for the growth of bacteria. You may have heard the myth that the number of bacteria is 10 times the number of cells in the human body. The human body weighs 70 kilograms and grows 170 centimeters contains about 30 trillion cells and 39 trillion intestinal bacteria. Although the ratio is not 1:10, the number is still impressive.

    Why do we need bacteria


    The human digestive system is designed to break down all incoming food into simple molecules: make them available for absorption by cells and into the bloodstream. At the same time, there are substances that our body cannot digest - complex carbohydrates.

    Complex carbohydrates are made up of long chains of sugar molecules that the digestive tract enzymes cannot break. There is simply no information in the human genome about compounds that break down complex carbohydrates, but genes from gut bacteria encode tens of thousands of such enzymes (polysaccharide lyases).

    And, it would seem, why do we need complex carbohydrates, even if our DNA does not say what to do with them? In the process of splitting complex carbohydrates, bacteria synthesize vitamins and short chain fatty acids - the main source of energy for intestinal cells. A person with bacteria has beneficial cooperation: we feed them, and they feed us.



    Another plus of this cohabitation is that the genetic material of bacteria is more flexible. These microorganisms adapt much more quickly to environmental changes, unlike humans. A vivid example of this, although negative for us, is the resistance of bacteria to antibiotics, which is now being observed more and more often.

    How does microbiota work?


    We have already mentioned that intestinal bacteria help to absorb fiber, produce short chain fatty acids and vitamins. You may feel that every bacterium does all this, but it is not.

    Microbiota is an entire ecosystem with its own rules and laws. It can be compared with a metropolis whose residents have a variety of professions. Part of the bacteria works for the good of the whole city and monitors pathogenic microorganisms so that they do not disturb the order and arrange a revolution. Some bacteria are passive: they do not benefit the city, but they do not create problems. And the third part is constantly plotting a plan on how to capture the city and plunder everything acquired. Which of these three representatives will be more depends on our diet.

    Complex carbohydrates are food for law-abiding microbiota citizens who care about their home. True, this is not a finished dish that we serve on a plate. For such tiny creatures, a complex carbohydrate molecule looks more like a felled oak. To remove branches, prepare a log, cut it, make firewood and matches, you need a variety of types of bacteria.



    If some kind of bacteria is not enough, the process of splitting carbohydrates, the synthesis of short-chain fatty acids and vitamins will be less effective. Therefore, the more different types of fiber foods we eat, the higher the variety of beneficial bacteria and the more stable the situation in the city, despite minor hooliganism from pathogenic microorganisms.

    Recently, more and more studies are appearing on how intestinal bacteria affect our lives. In the next article, we will talk about the most common genera of bacteria that live in the intestines of people, and how they work.

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