Dhe large intestine is home to a tremendous amount of microorganisms that are essential for digestion. In order to avoid reciprocal attacks between the intestinal flora and the uppermost cell layer of the large intestine – the intestinal epithelium – tissue and microorganisms must be kept at a distance despite their dependencies. The intestinal mucosa takes on this task. Without a clear distinction between the intestinal flora and the intestinal epithelium, there is a risk of chronic inflammation such as ulcerative colitis or Crohn’s disease, because the immune system is then constantly involved in skirmishes with the intestinal flora.
Until now it has been believed that the mucus is mainly produced in the last section of the colon. It is unclear whether the intestinal mucous membrane and the mucus it secretes merely form a boundary layer or perform other tasks. It is also unclear whether the same spacing rules apply to the intestinal flora and epithelium or whether there are differences between the individual areas of the large intestine.
Scientists working with Kirk Bergstrom from the “Oklahoma Medical Research Foundation” answer some of these questions in the journal “Science”, in mice. Their results show that it is not the last section of the intestine that is responsible for the best separation between the intestinal flora and the intestinal epithelium, but the first part, which is closer to the small intestine. Different types of mucus are also formed. Mucus production and bacterial community also influence each other.
Double slime cover offers better protection
In mice, the intestinal flora itself ensures that they are kept at a distance immediately after the faecal mud passes into the large intestine. Bergstrom and his colleagues base their findings on a new form of imaging in which all sections of the mouse large intestine can be examined simultaneously, including the respective mucus composition. It was found that the mice produce a thick mucus in the ascending branch of the large intestine, whereas in the descending branch that leads to the anus, it is thin. The tough mucus not only lines the intestinal wall in the ascending branch, but also immediately envelops the fecal pellets formed from the faecal pulp, together with the entrapped intestinal bacteria. This creates a further compact barrier between the intestinal flora and intestinal epithelium in addition to the mucous membrane in the ascending branch.
In the descending branch of the large intestine, this covering is then supplemented with a second layer of thin mucus. Mice solve the distance problem with double packaging of the excrement pellets. The mucus thus moves through the intestines together with the excretions.
Bergstrom’s researchers have also found that the composition of the tough mucus depends directly on the composition of the intestinal flora. This is not the case with thin secretions. Conversely, the quality of the bacterial community also depends on the quality of the mucus. In mice, mucus and intestinal flora determine the stability of the barrier between the microorganisms and the intestinal epithelium. Without the right composition on both sides, the shell becomes permeable, which leads to inflammation of the organ.