The wall of the small intestine produces phlegm, which protects against the sour food paste. The mucus contains enzymes which are responsible for the fine cleavage of the foodmolecule that has been digested by the digestive juice or by some sugars, such as sucrose (beet sugar), maltose (e.g. present in bread) or lactose (milk sugar).
The digestive juices produced in 24 hours correspond to a volume of 7-10 litres of water in which a quantity of mineral salts are dissolved. These digestive juices are almost completely reabsorbed in the large intestine. The large intestine also has a pronounced bacterial flora (the intestinal flora), which is important for digestion and produces vitamine in particular.
https://de.wikipedia.org/wiki/Verdauungstrakt (Wikipedia CC-by-sa-3.0)