Updated: 12/29/2015

Carbohydrate Digestion

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Overview
  • Overview
    • dietary carbohydrates include polysaccharides, disaccharides, and monosaccharides
      • intestinal epithelial cells absorb only monosaccharides
        • glucose, galactose, and fructose
  • Digestion of dietary polysaccharides
    • salivary secretions
      • salivary α-amylase initiates digestion of polysaccharides in mouth
        • digests interior α-1,4 glycosidic linkages, yielding 3 disaccharides
          • α-limit dextrins, maltose, and maltotriose
      • salivary α-amylase plays a minimal role in digestion of carbohydrates
        • low pH of gastric contents quickly inactivates salivary α-amylase
    • pancreatic secretions
      • pancreatic juices are secreted into lumen of duodenum of small intestine
      • pancreatic α-amylase initiates digestion of polysaccharides in the small intestines
        • digests interior α-1,4 glycosidic linkages, yielding 3 disaccharides
          • α-limit dextrins, maltose, and maltotriose
    • intestinal mucosa
      • intestinal brush border enzymes initiate digestion of disaccharides to monosaccharides
        • α-dextrinase catalyzes α-limit dextrins → glucose
        • maltase catalyzes maltose → glucose
        • sucrase catalyzes maltotriose → glucose
      • intestinal epithelial cells absorb glucose, a monosaccharide
  • Digestion of dietary disaccharides
    • dietary disaccharides include trehalose, lactose, and sucrose
    • dietary disaccharides do not require α-amylase digestion
    • intestinal brush border enzymes initiate digestion of disaccharides to monosaccharides
      • trehalase catalyzes trehalose → glucose + glucose
      • lactase catalyzes lactose → glucose + galactose  
      • sucrase catalyzes sucrose → glucose + fructose
    • intestinal epithelial cells absorb glucose, galactose, and fructose, all monosaccharides
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Questions (1)

(M1.GI.15.75) A 13-year-old boy presents to his physician for a routine visit. He states that he feels well and has no major complaints. On review of systems, he does note that he seems to have significant belly pain and increased flatulence whenever he eats any dairy products and thus has stopped consuming them. The pediatrician explains that he most likely has an enzyme deficiency. If a small bowel biopsy were to be performed on this patient, which of the following figures most accurate demonstrates the histology that would be observed? Tested Concept

QID: 106748
FIGURES:
1

Figure A

15%

(27/176)

2

Figure B

3%

(6/176)

3

Figure C

2%

(4/176)

4

Figure D

66%

(117/176)

5

Figure E

10%

(17/176)

M 1 D

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