Intestinal epithelial cells form the interface between the intestinal lumen (mucosal side) and the blood (serosal side) and have many different receptors and channels that allow various molecules to flow in both directions.
Some of these channels allow passive transport, others active transport. Passive transport occurs freely, according to concentration: molecules move from more concentrated to less concentrated solutions until an equilibrium is reached. Active transport occurs against a gradient and requires energy.
Some transport only one type of molecule, others can transport more than one.
A popular way of studying glucose transport is by the use of blockers. One such blocker, ouabain, is able to block the sodium-potassium ATPase.
Figure 1: Glucose transport between the mucosal and serosal sides of the intestine.