3.4.2.1. Digestion

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.

Last modified: Wednesday, 18 April 2012, 9:58 AM