The digestive system is one of the eight systems of our body, and the digestive system consists of the digestive tract and digestive glands. The digestive tract includes the well-known mouth, pharynx, esophagus, stomach, small intestine, and large intestine; while the digestive glands mainly include salivary glands, liver, pancreas, etc. They make up the entire digestive system of the human body.
The digestive system is responsible for the digestion and absorption of food. Digestion is the process of breaking down the macromolecular substances of food into absorbable small molecular substances through mechanical or chemical processes; while absorption is the process of these small molecular substances entering the blood and lymph.
The oral cavity is mainly responsible for digestion, which is mainly divided into mechanical chewing and weaker salivary digestion, where food eaten in the mouth is chewed, ground, and then mixed with saliva to form a bolus, which is swallowed through the pharynx and esophagus into the stomach. Saliva has many functions, among which its digestive function should be well known. Salivary amylase can separate starch into maltose.
The stomach has both mechanical digestion and chemical digestion. The movement of the stomach maintains the shape of the stomach and adapts to the temporary storage of large amounts of food while mixing and grinding food to form chyme. There are mainly hydrochloric acid and some digestive enzymes in gastric juice. Hydrochloric acid can activate pepsin to play its role in digesting proteins by hydrolyzing it. It can also promote the digestion of the small intestine by promoting the secretion of pancreatic juice and bile.
The small intestine is an important part of both digestion and absorption. The movement of the small intestine is mainly to maintain the shape of the intestine and promote the mixing of intestinal contents while propelling the chyme forward. The small intestine can absorb water, inorganic salts, sugars, proteins, fats, as well as cholesterol, and most vitamins.