So we see that even though the veins have the same exact three layers as our arteries, the veins have a much thinner tunica media. And they also have this system of one wave valves in place to prevent the movement of our blood back down our vein as a result of the force of gravity. Now, what about the third type of blood vessel, our capillaries? Well, capillaries are actually very, very tiny blood vessels. They're the smallest blood vessels found inside our body, and in fact, they're only a single layer thick. So they have a single cell layer, as we'll see in just a moment.