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. Now, why is that important? Well, it turns out that capillaries are specialized blood vessels where we have the exchange of nutrients and waste products taking place between the cells, the tissues, and the organs of our body. And these capillaries actually connect the tiny arterials to our tiny venue.