Question

Describe the process by which gut epithelial cells use transporters to take up ingested glucose (apical membranes) and distributes glucose to other tissues by moving it back out of the cell (basal membrane). This process involves active transport and passive as discussed in class. Also describe how tight junctions help to make this process efficient.

Answer 1

Gut epithelial cells uses two different transporters located at two opposite sides of the cell and thus is said to be polarised.

A) apical side of the cell facing the gut which is specialised for absorption, has Na+-glucose-symporter . It couples the entry of sodium ions down its electrochemical gradient to the active transport of glucose against its concentration gradient from the intestinal lumen. This supporter, thus, couples energetically unfavourable inward movement of one glucose molecule to the energetically favourable inward movement of 2 sodium ions. This symporter is restricted to the apical side of the cell due to tight junctions in the neighbouring apical cells.

B) second transporter GLUT2 is located on the lateral and basal surface, commonly called as basolateral side. It helps in the movement of glucose out of the cells down its concentration gradient. It is uniporter i.e., glucose is transported from the cell to the extracellular matrix. Importer is also restricted by the presence of tight junctions that prevents diffusion of glucose back into the lumen of the gut.