Glukosabsorption

Glukosabsorption, or glucose absorption, is the uptake of glucose and other monosaccharides from the intestinal lumen into the bloodstream. It occurs mainly in the small intestine, especially the jejunum, with some contribution from the duodenum and ileum. The absorbed glucose is a principal energy source for body cells.

The principal mechanism involves active transport at the intestinal brush border. The apical Na+-glucose cotransporter SGLT1 (SLC5A1) carries glucose into enterocytes against its concentration gradient using the inward Na+ gradient established by the Na+/K+ ATPase on the basolateral membrane. Once inside the enterocyte, glucose exits across the basolateral membrane via facilitated diffusion through transporters such as GLUT2, and to a lesser extent GLUT1 or GLUT3 in certain conditions. Under high luminal glucose, GLUT2 can be inserted into the apical membrane, enhancing uptake. Other sugars follow separate routes: fructose is absorbed via GLUT5 on the apical side and exits through GLUT2 on the basolateral side.

Disaccharides from diet are first hydrolyzed by brush border enzymes, yielding glucose, galactose, and fructose for absorption. Overall absorption efficiency depends on luminal sugar concentration, intestinal surface area, mucosal integrity, and digestion efficiency. Impairment of absorption can arise from mucosal diseases, surgical shortening of the intestine, or genetic disorders.

Clinical relevance includes congenital glucose–galactose malabsorption caused by SGLT1 mutations, which leads to severe osmotic diarrhea in infancy. In contrast, normal glucose absorption is essential for energy balance and nutrition, and is an important consideration in disorders affecting the gut mucosa or transporter function.