Bolus
The food bolus is that mush of food mixed with saliva that is formed in the mouth during chewing, thanks to the mechanical activity of the teeth, compacting the tongue and lubricant of the saliva. Salivary enzymes, for their part, operate a partial digestion of food, transforming starches into oligosaccharides and dextrins. Every single bite is then rendered unrecognizable by the masticatory activity which, when particularly prolonged, gives starchy foods a sweet taste, a sign of their partial digestion with the release of oligosaccharides (which have a discreet sweetening power). The final result of all these processes is a mixture of shredded, chopped and partially digested food, called the bolus.
In light of all these important modifications, suffered by the foods inside the oral cavity, the bolus is considered the first product of digestion.
During swallowing, the bolus is pushed towards the pharynx, while a series of involuntary contractions prevent its ascent and descent into the upper and lower airways.
Once past the upper esophageal sphincter, the bolus is channeled into a small tube about 24 cm long called the esophagus, which descends pushed by peristaltic contractions until it reaches the gates of the stomach.
Chimo
Once in the stomach, the bolus is kneaded and mixed with acids and digestive enzymes, such as pepsin and gastric lipase. After a period varying from two to five hours (depending on the quantity and nature of the ingested food), what was once defined as a bolus has become a particularly acidic, brothy liquid called chyme. Inside it there are digestive enzymes, a certain amount of hydrochloric acid and partially digested food, especially in the protein fraction (pepsin secreted by the stomach is a key enzyme in protein digestion). Hydrochloric acid, for its part, determines the killing of most of the ingested microorganisms, facilitates the digestion of the proteins and that of the raw starch.
Chilo
After gastric digestion, the chyme coming from the stomach is gradually pushed into the first part of the small intestine, called the duodenum. This passage does not occur abruptly, but in small successive waves, so as not to overload the enteric systems of absorption and digestion.
In the duodenum the products of important glands are poured, such as the pancreas (pancreatic juice), the liver (bile) and the intestinal glands (enteric juice). From the mixture between the chyme acid and these secretions originates the kilo, a milky, slightly basic liquid, rich in nutrients and enzymes involved in the final phase of digestion.
Ultimately, the enzymatic action produces elementary nutrients of particularly small size, which allow it to pass through the intestinal mucosa and flow into the blood or lymph (where the lipids and the other fat-soluble components are poured in the form of chylomicrons) .
Once in the final part of the small intestine, called the ileum, the kilo is now poor in nutrients, which have been removed from the intestinal villi of the duodenum and the subsequent tracts of the small intestine (jejunum and ileum).
Abandoning the small bowel, the journey of kilo continues towards the large intestine, where it is deprived of water and mineral salts, attacked by the intestinal flora, enriched with mucus and flaked cells, until it becomes a waste product called feces. These scraps, driven by peristaltic movements, are accumulated in the fecal ampulla and from there channeled at the opportune moment into the rectum, which expels them outside through the anus.
