Now most of the time within our organs we have a single system of capillaries but sometimes in certain organs we have a portal system and that simply means we have two consecutive network of capillaries that are next to one another. Now we have several portal systems in our body as we'll discuss in the next several lectures. We have one in our brain, we also have one in the kidneys and our small intestine. Now the final thing that I'd like to mention is the pathway that the blood actually follows within our cardiovascular system. So here we're going to show that the cardiovascular system of the human body is in fact a closed circuit. So let's take a look at the following diagram which basically describes the simplified diagram for the cardiovascular system.