2023-06-24 11:00:00
The terminus of the digestive tract (large intestine), comprising caecum, colon, rectum and anus, measures approximately 1.5 m. Only the non-reabsorbed chyme residues arrive there, therefore the waste products of digestion such as dietary fibres, minerals…
This waste crosses, to achieve this, a kind of airlock consisting of two folds of the mucous membrane which open in one direction. From this moment, digestion slows down, and begins a quiet mode. After spending 2 to 6 hours in the stomach, then 1 or 2 hours in the small intestine, what remains of the food will settle for a day or two. Every 3 minutes, the walls contract, knead and push the residues, while a maximum of water (laden with mineral salts) is reabsorbed via the mucous membrane. Thus, as they progress, these residues thicken, and become loaded with various waste products, such as mucosal cells, bacteria, etc.
The route of the residues to the disposal
Still liquid in the right colon (or ascending colon), the residues become solid when entering the left colon (or descending colon). In all this space, there is no trace of nutrient assimilation. However, bacteria swarm, since it is the place dedicated to the intestinal flora which weighs between 1.5 and 2 kg! Some of these bacteria have their own enzymes which will digest the last traces of nutrients, produce substances such as vitamin K (involved in blood clotting), but which can also release gas like hydrogen or methane, at the origin of these flatulences which disturb us: we produce from 400 to 1400 ml per day of gas, odorous because of sulfur derivatives. Over the course of the contractions, the faeces fragmented into sorts of “balls”, which, once they reached the end of the colon, approached read right. This last segment of the intestine, regarding 12 cm long, stores faeces at the level of the rectal ampulla capable of dilation, and closed by the anal sphincter, a sort of muscular ring. When a sufficient quantity of excrement has accumulated there, it puts pressure on the internal sphincter, which relaxes and triggers the urge to go to the toilet, but also the contraction of the external sphincter allowing stool to be retained (the continence). It is once installed and ready that this external sphincter is released, voluntarily, to allow evacuation.
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