Meta-Biol

• Pathways

Hexoses, notably fructose, glucose, and galactose generated in the lumen of the small intestine by breakdown of dietary carbohydrate, are taken up by enterocytes lining the microvilli of the small intestine and released from them into the blood. Uptake into enterocytes is mediated by two transporters localized on the luminal surfaces of the cells. SLC5A1, also known as SGLT1, mediates the co-transport of sodium ions and glucose and galactose, and SLC2A5, also known as GLUT5, mediates fructose uptake (Wright 1998). Tetrameric SLC2A2, also known as GLUT2, localized on the basolateral surfaces of enterocytes, mediates the release of these hexoses into the blood (Kellett & Brot-Laroche 2005; Wright et al. 2004).

Nutrient absorption occurs mostly in the small intestine. Processes annotated here include the uptake of dietary cholesterol and phytosterols, and of monosaccharides. Movement of the final products of digestion out of the intestinal lumen is mediated by arrays of transporters associated with the apical and basolateral surfaces of enterocytes (Yamada 2015).

Fats, carbohydrates, and proteins are broken down to small molecules - fatty acids, cholesterol, and glycerol, monosaccharides, and amino acids - within the lumen of the gastrointestinal tract and absorbed into the body principally through enterocytes in the small intestine. Some of the hydrolases that catalyze these reactions are secreted into the gastrointestinal tract; others are associated with the luminal surfaces of enterocytes. Movement of the final products of digestion out of the intestinal lumen is mediated by arrays of transporters associated with the lumenal and basolateral surfaces of enterocytes (Yamada 2015).