Absorption and digestive processes
Summary of uptake and digestion processes:
Protein
- Cleavage by the pepsin enzyme and hydrochloric acid in the stomach
- Initially stops in the duodenum due to nearly neutral ph value
- Admixture by the enzymes trypsinogen and chymotrysinogen (from the pancreas) as well as carboxypeptidase and aminipeptidase. These enzymes are activated in the duodenum and split up the long-chain amino acids into individual amino acids in several steps. Now the individual amino acids are quickly absorbed by the jejunum wall
Carbohydrates
- Splitting of carbohydrates begins in the mouth with the help of the alpha-amylase enzyme contained in the saliva (complex sugars are broken into separate chunks/pieces of sugar)
- Carbohydrate digestion stops in the stomach
- In the duodenum alpha-amylase (from the pancreas) is added again
- The multiple-sugar fragments are then split into individual sugars (maltose, lactose, sucrose). These are then absorbed by the wall of the small intestine and flow to the liver together with the blood
Fats
- Initial / pre-splitting in the stomach with the help of the lipase enzyme
- The largest and final part takes place in the jejunum, after bile acids and pancreatic juices have been added in the duodenum
- The pancreatic lipase enzyme splits fats (tryglycerides) into monoglycerides and free fatty acids
- Monoglycerides, fatty acids, cholesterol, phospholipids and fat-soluble vitamins (E, D, K, A) are, under the influence of bile acids, deposited on the villi in the form of “tiny drops”
- Uptake of fats predominantly takes place in the duodenum and partly in the jejunum
Electrolytes
- The electrolytes (Na, K, Mg, Cl) found in the small intestine mainly come from the digestive juices added in the intestine and only a small part comes from food and drink
- Are predominantly absorbed in the jejunum (partly actively, partly passively)
- Water passively follows the reabsorbed electrolytes
Vitamins
- Fat-soluble vitamins (E, D, K, A) are only absorbed when other fats are present
- Water-soluble vitamins are absorbed in the jejunum
- Vitamin B12 can, however, only be absorbed in the ileum with the intrinsic factor enzyme produced in the stomach