As explained in Chapter 65, the final products of carbohydrate digestion in the alimentary tract are
almost entirely glucose, fructose, and galactose—with glucose representing, on average, about 80
percent of these. After absorption from the intestinal tract, much of the fructose and almost all the
galactose are rapidly converted into glucose in the liver. Therefore, little fructose and galactose are
present in the circulating blood.
Glucose thus becomes the final common pathway for the transport of
almost all carbohydrates to the tissue cells. In liver cells, appropriate enzymes are available to
promote interconversions among the monosaccharides—glucose, fructose, and galactose—as shown in
Figure 67-3. Furthermore, the dynamics of the reactions are such that when the liver releases the
monosaccharides back into the blood, the final product is almost entirely glucose.
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