Carbohydrate digestion (brush border enzymes, end products) & Carb absorption (fructose, galactose)

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• Carbohydrate digestion concludes in microvilli of the small intestine, in brush border epithelial cells. Carbohydrate digestion -brush border enzymes • Four brush-border enzymes are involved: • Alpha-dextrinase breaks down alpha-dextrin chains by removing glucose units. • Sucrase breaks sucrose into glucose and fructose. • Maltase breaks maltose and maltotriose into glucose. • Lactase breaks lactose into glucose and galactose. • The final end products of carbohydrate digestion are glucose, fructose, and galactose. • All end products of carbohydrate digestion (glucose, fructose, and galactose) are absorbed as monosaccharides. • Carbohydrates are ultimately absorbed into capillaries of the villi. • Facilitated diffusion: • Transports fructose from lumen into epithelial cells of intestinal villi. • Transports monosaccharides out of epithelial cells into the interstitial fluid. • The monosaccharide eventually diffuses into the blood stream without using ATP in the process. • Secondary active transport: • Transports glucose and galactose into epithelial cells of intestinal villi. • Couples transport of glucose or galactose with that of sodium ions. • Transports materials in the same direction, down the concentration gradient for at least one substance. • Glucose and galactose are then transported from epithelial cells to the interstitial fluid and eventually into the blood via facilitated diffusion.

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