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AccessibilityDuodenum
The duodenum is the first section of the small intestine. It is only about 30 cm (12 inches) long, hence its name which comes from the Latin for 'twelve'. It has the same four-layered wall of mucosa, submucosa, muscle layer and serosa as the rest of the gut.
The main function of the duodenum is digestion. Within its short length, the liquid chyme from the stomach is broken down into small molecules. These can then be absorbed into the body in the remainder of the small intestine.
The first stage in the digestive process is the neutralisation of the acidic chyme. This is necessary because the digestive enzymes of the duodenum require alkaline conditions to work.
The chyme is neutralised by bicarbonate in the bile. Bile is produced in the liver and stored in the gall bladder. It enters the duodenum via the bile duct. Bile also contains bile salts that begin the digestion of fats. Bile is sometimes refluxed from the duodenum into the stomach and also into the oesophagus where it can cause erosion and pain, like refluxed gastric juice.
Digestion is completed by enzymes secreted by the wall of the duodenum, and by pancreatic enzymes, which enter the duodenum via the pancreatic duct. Individual enzymes are specific for particular types of foods: lipases for fats (lipids), amylases for carbohydrates, and proteases for proteins. Enzymes break down the large food macromolecules into simple molecules, which can then be absorbed by the small intestine.
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Food Carbohydrate Protein Fats (lipids) |
Enzymes Amylases Proteases Lipases |
Product of digestion Glucose and other monosaccharides Amino acids Fatty acids and glycerol |
