Sources

Examples of disaccharidases:

• Lactase (breaks down lactose into glucose and galactose)
• Maltase (breaks down maltose into 2 glucoses)
• Sucrase (breaks down sucrose into glucose and fructose)
• Trehalase (breaks down trehalose into 2 glucoses)

Only monosaccharides (glucose, galactose, fructose) are absorbed by enterocytes.

Glucose and galactose are taken up by SGLT1 (Na+ dependent). Fructose is taken up by facilitated diffusion by GLUT-5.

All are transported to blood by GLUT-2.

D-xylose absorption test: distinguishes GI mucosal damage from other causes of malabsorption.

GLUT-2 has Km for glucose of -15mM (lowest affinity). The rest are -1 to 5mM

Only GLUT-4 (in m/s cells & adipocytes) works in response to Insulin

GLUT-4 translocation to the cell membrane in skeletal muscle is stimulated by exercise.

This effect, which is independent of insulin, involves a 5′ AMP-activated kinase

Glycolysis

A cytoplasmic series of reactions by which glucose, a six-carbon sugar is metabolised to two molecules of the three-carbon unit, pyruvate.

Non-glucose monosaccharides (eg, galactose, mannose, fructose) enter the glycolytic pathway at different points as intermediates of glycolysis. Of these, frctose is the only one whose metabolites bypass phosphofructokinase, one of the key enzyme involved in regulating the rate of glycolysis. As a result, fructose is metabolized by the liver FASTER than the other monosaccharides and is rapidly cleared from the bloodstream following dietary absorption.