The absorption of glucose from the small intestinal lumen to the blood is coupled to sodium transport and is very energy costly. What protein actively transports sodium, using ATP, therefore setting up the sodium gradient that drives the cotransport of glucose and other nutrients? Consider three compartments, the small intestinal lumen, the interior of the epithelial cell, and the interstitial fluid. Which compartment has the lowest sodium concentration?

With reference to these three compartments, describe how glucose is transported into the blood.