Glucose Absorption Into the Small Intestine

Glucose is absorbed into the small intestine via transcellular transport, which takes place in two stages — import into the intestinal epithelial cells from the apical side and subsequent export through the basolateral side.

Import begins with the binding of two sodium ions from the intestinal lumen to the sodium-glucose symporter — SGLT1. This allows one glucose molecule to bind against its concentration gradient.

After releasing the bound sodium ions and glucose molecule inside the cell, the transporter reverts to its original conformation.

The intracellular glucose is exported out of the cell via facilitated transport through the GLUT2 uniporter located on the basolateral membrane.

To maintain a low cytosolic sodium concentration, the sodium/potassium pump on the basolateral side actively pumps out three sodium ions from the cell in exchange for two potassium ions.

In order to regulate the intracellular potassium concentration, the potassium channels present on the basolateral domain continuously pump the excess potassium ions out of the cell.

In this way, glucose crosses the epithelial cells and reaches the bloodstream for circulation.