Multiple choice

Which of the following is the correct order of absorption rate of the monosaccharides by the intestinal mucosa?

  1. Arabinose > Xylose > Mannose > Fructose > Glucose > Galactose

  2. Glucose > Fructose > Galactose > Mannose > Xylose > Arabinose

  3. Galactose > Fructose > Glucose > Mannose > Xylose > Arabinose

  4. Galactose > Glucose > Fructose > Xylose > Mannose > Arabinose

  5. Glucose > Fructose > Galactose > Xylose > Arabinose > Mannose
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D Correct answer
Explanation

Glucose and galactose are absorbed mainly by the jejuna enterocytes, against a concentration gradient, by a sodium-dependent active transport mechanism. Fructose crosses the apical membrane of enterocytes of the jejunum by facilitated (mediated) diffusion. Since this transfer is not energy dependent, fructose cannot be absorbed against a concentration gradient. Limited absorption of xylose, mannose, and arabinose seems to occur by a diffusion mechanism. This difference in mechanism of absorption of monosaccharides accounts for their absorption by the intestinal mucosa.

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