If Na+ levels were depleted in the extracellular fluid, what effect would it have on glucose movement?

Depleting Na+ levels in the extracellular fluid would decrease the rate of glucose movement primarily due to the reliance of many glucose transport mechanisms on sodium gradients. Many glucose transporters, such as the sodium-glucose symporter (SGLT), utilize the sodium concentration gradient to drive the uptake of glucose into cells. This mechanism depends on the presence of Na+ ions outside the cell, which creates a favorable gradient for sodium to enter the cell along with glucose.

When Na+ levels are depleted, the gradient necessary for the symporters to function effectively is disrupted. As a result, the ability of cells to uptake glucose through these sodium-dependent mechanisms diminishes. Consequently, without sufficient Na+ levels, glucose transport into cells would be reduced, leading to a decrease in the overall rate of glucose movement. This explains why the correct response is that the depletion of Na+ levels would decrease the rate of glucose movement.