This is basically a secondary active transport, and we'll see exactly what we mean by that in just a moment. Basically, an ATPA pump is used to establish an electrochemical gradient for sodium. And then as the sodium moves down its electrochemical gradient, it basically brings the amino acid with it. Now, for the case of dipeptides and tripeptides, instead of using the sodium dependent system, we use a hydrogen ion dependent cotransporter system and we'll see exactly what that means in just a moment. So basically, in this system, we have to use a hydrogen sodium exchange system, where we establish a proton gradient, a hydrogen ion electrochemical gradient, and we use that gradient to basically transport the dipeptides and tripepptide. So, to see exactly what we mean, let's look at the following diagram.