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3.4B: Carbohydrate Digestion in the Small Intestine

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    1462
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    The small intestine is the primary site of carbohydrate digestion. Pancreatic alpha-amylase is the primary carbohydrate digesting enzyme. Pancreatic alpha-amylase, like salivary amylase, cleaves the alpha 1-4 glycosidic bonds of carbohydrates, reducing them to simpler carbohydrates, such as glucose, maltose, maltotriose, and dextrins (oligosaccharides containing 1 or more alpha 1-6 glycosidic bonds). Pancreatic amylase is also unable to cleave the branch point alpha 1-6 bonds1.

    Figure 3.421.png

    Figure 3.421 The function of pancreatic amylase

    The pancreatic amylase products, along with the disaccharides sucrose and lactose, then move to the surface of the enterocyte. Here, there are disaccharidase enzymes (lactase, sucrase, maltase) on the outside of the enterocyte. Enzymes, like these, that are on the outside of cell walls are referred to as ectoenzymes. Individual monosaccharides are formed when lactase cleaves lactose, sucrase cleaves sucrose, and maltase cleaves maltose.

    Figure 3.422 .png

    Figure 3.422 Products of pancreatic amylase

    There is also another brush border enzyme, alpha-dextrinase. This enzyme cleaves alpha 1-6 glycosidic bonds in dextrins, primarily the branch point bonds in amylopectin. The products from these brush border enzymes are the single monosaccharides glucose, fructose, and galactose that are ready for absorption into the enterocyte1.

    Figure 3.423.png

    Figure 3.423 Disaccharidases on the outside of the enterocyte.

    References & Links

    1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.

    This page titled 3.4B: Carbohydrate Digestion in the Small Intestine is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Brian Lindshield via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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