VPB 121: Veterinary Physiology - II (2+1)

CARBOHYDRATE ABSORPTION

Carbohydrate absorption

• Monosaccharides (eg. glucose, fructose) are absorbed by active transport mediated by carrier and sodium pump.

Absorption of glucose

• Glucose gets attached to specific transport proteins that lie on the luminal side of the enterocytes. These transport proteins have two binding sites one for glucose and one for sodium.

• Once glucose and Na⁺ occupy the binding sites, the transport protein moves across the cell membrane and unload the glucose and Na⁺ into the cell. Hence, this process is referred to as sodium co-transport.
• The transport of glucose will not occur unless Na+ is present.
• Within the cell, glucose moves down by concentration gradient through the basoleteral membrane by facilitated diffusion, to extra-cellular space and then into the blood and finally to liver  where the monosaccharides are stored as glycogen.
• Galactose is absorbed more rapidly than glucose but fructose absorption is slower than glucose absorption.
• Fructose absorption is by facilitated diffusion and not energy dependent. Hence, fructose can not be absorbed against concentration gradient.
• Mannose, xylose and arabinose are poorly absorbed by diffusion.
• Maltose, sucrose and lactose as such are absorbed very slightly.
• Disaccharides do not generally enter into the blood stream because of the presence of disaccharidases in the brush border of mucosa, which converts them to monosaccharides.