Site pages
Current course
Participants
General
Topic 1
Topic 2
Topic 3
Topic 4
Topic 5
Topic 6
Topic 7
Topic 8
Topic 9
Topic 10
Topic 11
Topic 12
Topic 13
Topic 14
Topic 15
Topic 16
Topic 17
Topic 18
Topic 19
Topic 20
Topic 21
Topic 22
Topic 23
Topic 24
Topic 25
Topic 26
Topic 27
3.4.2.1. Digestion
Starch and glycogen are completely hydrolyzed by enzyme action in the gastrointestinal tract to yield free D-glucose. This process begins in the mouth during chewing, through the action of amylase (Ptyaline) secreted by the salivary glands. Salivary amylase hydrolyzes many of the α (1–4) glycosidic linkages of starch and glycogen to yield a mixture of maltose, glucose and oligosaccharides. Ptyaline action continues in the swallowed food bolus until gastric HCl inactivates it near pH 4.0.
Amylase from saliva, Starch--------------------------→ Maltose + Oligosaccharides + monosaccharides Pancreas and intestinal juices
The digestion of digestible polysaccharides to yield D-glucose is continued and completed in the small intestine, largely by the action of pancreatic amylase, made by the pancreas and secreted via the pancreatic duct into the upper portion of the small intestine. This segment of the small intestine in which most of its digestive activity occurs, is called the duodenum. Disaccharides are hydrolyzed by enzymes located in the outer border of the epithelial cells lining the small intestine. Sucrose is hydrolyzed to D-glucose and D-fructose by sucrase, also called invertase: lactose is hydrolyzed to D-glucose and D-galactose by lactase or β-galactosidase and maltose is hydrolyzed by maltase yielding two molecules of D-glucose. Maltase Maltose → two molecules of glucose. Lactase Lactose → glucose and galactose. Sucrase Sucrose → glucose and fructose. |