A group of organs is involved in the digestive process, which is divided into two major divisions: the digestive glands (salivary glands, liver and pancreas glands) and the gastrointestinal tract. Digestive enzymes are divided into three main groups: proteases, lipases, and amylases. Among the functions of the digestive tract are the promotion of food, absorption and elimination of undigested food residues from the body. The digestive process begins in the oral cavity. During chewing, the food supplied during the feeding process is crushed and moistened with saliva, which is produced by three pairs of large glands (sublingual, submandibular and parotid) and microscopic glands located in the mouth. Saliva contains the enzymes amylase and maltase, which break down nutrients. Thus, the process of digestion in the mouth consists in physically crushing food, chemically affecting it and moistening it with saliva for ease of swallowing and continuing the digestion process.

The process of digestion in the stomach begins with the fact that food, crushed and moistened with saliva, passes through the esophagus and enters the organ. For several hours, the food lump experiences mechanical (muscle contraction when moving into the intestine) and chemical effects (gastric juice) inside the organ. Gastric juice consists of enzymes, hydrochloric acid and mucus. The main role belongs to hydrochloric acid, which activates enzymes, promotes the fragmentary breakdown of proteins, has a bactericidal effect, destroying a lot of bacteria. The enzyme pepsin in the composition of gastric juice is the main one, breaking down proteins. The action of mucus is aimed at preventing mechanical and chemical damage to the organ membrane. The composition and amount of gastric juice will depend on the chemical composition and nature of the food. The sight and smell of food promotes the release of the necessary digestive juice. As the digestion process progresses, the food is gradually and portioned into the duodenum.

The digestive process in the small intestine begins in the duodenal cavity, where the food lump is affected by pancreatic juice, bile and intestinal juice, since it contains the common bile duct and the main duct of the pancreas. Inside this organ, proteins, carbohydrates and fats are digested to monomers (simple compounds), which are absorbed by the body. Learn more about the three components of chemical exposure in the small intestine. Pancreatic juice contains the protein-cleaving enzyme trypsin, which converts fats into fatty acids and glycerol, the enzyme lipase, as well as amylase and maltase, which break down starch into monosaccharides. Bile is synthesized by the liver and accumulates in the gallbladder, from where it enters the duodenum. It activates the enzyme lipase, participates in the absorption of fatty acids, increases the synthesis of pancreatic juice, activates intestinal motility. Intestinal juice is produced by special glands in the inner lining of the small intestine. It contains more than 20 enzymes. There are two types of digestion in the intestine, and this is its peculiarity.: – cavitary – is carried out by enzymes in the organ cavity; – contact or membrane treatment is performed by enzymes that are located on the mucous membrane of the inner surface of the small intestine. Thus, the food substances in the small intestine are actually completely digested, and the final monomer products are absorbed into the blood. At the end of the digestive process, the digested remains of food penetrate from the small intestine into the large intestine.

The process of enzymatic processing of food in the large intestine is quite insignificant. However, in addition to enzymes, obligate microorganisms (bifidobacteria, E. coli, streptococci, lactic acid bacteria) are involved in the digestive process in the large intestine. Bifidobacteria and lactobacilli are extremely important for the body: they have a beneficial effect on intestinal function, participate in the breakdown of fiber, ensure the quality of protein and mineral metabolism, enhance the body’s resistance, have antimutagenic and anticarcinogenic effects. The intermediates of carbohydrates, fats, and proteins are broken down to monomers here. Colon microorganisms produce vitamins (groups B, PP, K, E, D, biotin, pantothenic and folic acids), a number of enzymes, amino acids and other substances. The final stage of the digestive process is the formation of fecal matter, which consists of 1/3 of bacteria, as well as epithelium, insoluble salts, pigments, mucus, fiber, etc.

Let’s focus on the nutrient absorption process separately. It represents the ultimate goal of the digestive process, when food components are transported from the digestive tract to the internal environment of the body – blood and lymph. Absorption occurs in all parts of the gastrointestinal tract. Absorption in the mouth is practically not carried out due to the short period (15-20 seconds) of food remaining in the organ cavity, but not without exceptions. In the stomach, the absorption process partially includes glucose, a number of amino acids, dissolved mineral salts, water, and alcohol.  Absorption in the small intestine is the most extensive, largely due to the structure of the small intestine, which is well adapted to the absorption function. Absorption in the large intestine concerns water, salts, vitamins and monomers (fatty acids, monosaccharides, glycerol, amino acids, etc.). The central nervous system coordinates all the processes of nutrient absorption. Humoral regulation is also involved in this. The process of protein absorption occurs in the form of amino acids and water solutions – 90% in the small intestine, 10% in the large intestine. Carbohydrates are absorbed in the form of various monosaccharides (galactose, fructose, glucose) at different rates. Sodium salts play a role in this. Fats are absorbed in the form of glycerol and fatty acids in the small intestine into the lymph. Water and mineral salts begin to be absorbed in the stomach, but this process proceeds more intensively in the intestines. Thus, the physiology of digestion encompasses the process of digestion of nutrients in the mouth, stomach, small and large intestines, as well as the process of absorption. Source >>