The free hexoses originating from the diet and from the hydrolysis of starch and disaccharides are rapidly absorbed all along the small intestine by crossing its wall. The process is very efficient and all of the monosaccharides (up to 120 g/h) are removed from the intestinal lumen before the remains of the meal reach the terminal part of the ileum. After absorption the sugar molecules cross the mucosal cells and enter the blood stream in the capillaries draining into the portal vein and finally, via the portal circulation, into the liver. The transport of glucose and galactose through the brush border of the intestinal mucosa is an active symport with Na+ but their transfer out of the cell into the interstitium and from there into the portal capillaries is by a simple and facilitated transport mechanism. The absorption of fructose is independent of Na+ and involves a facilitated diffusion.
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