Hydrolysis of Disaccharides and Small Glucose Polymers into Monosaccharides by Intestinal Epithelial Enzymes

enterocytes lining the villi of the small intestine contain four enzymes (lactase, sucrase, maltase, and a-dextrinase), which are capable of splitting the disac-charides lactose, sucrose, and maltose, plus other small glucose polymers, into their constituent monosaccha-rides.These enzymes are located in the enterocytes covering the intestinal microvilli brush border, so that the disaccharides are digested as they come in contact with these enterocytes.

Lactose splits into a molecule of galactose and a molecule of glucose. Sucrose splits into a molecule of fructose and a molecule of glucose. Maltose and other small glucose polymers all split into multiple molecules of glucose. Thus, the final products of carbohydrate digestion are all monosaccharides. They are all water soluble and are absorbed immediately into the portal blood.

In the ordinary diet, which contains far more starches than all other carbohydrates combined, glucose represents more than 80 per cent of the final products of carbohydrate digestion, and galactose and fructose each seldom more than 10 per cent.

The major steps in carbohydrate digestion are summarized in Figure 65-1.

Starches

— Pancreatic amylase-50-80%

Maltose and 3 to 9 glucose polymers Lactose Sucrose

Starches

— Pancreatic amylase-50-80%

Maltose and 3 to 9 glucose polymers Lactose Sucrose

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