In this video, we're going to begin our introduction to the lymphatic system, which is a system of lymphatic vessels and lymphoid organs distributed throughout our bodies. Now before we talk more about what the lymphatic system actually is, let's first talk about why do we even need it to begin with, especially knowing that we already have blood vessels of the cardiovascular system branching throughout practically our entire bodies. So why would we need a second set of lymphatic vessels? Well, it turns out that although the cardiovascular system is incredibly good at performing its functions that we talked about in previous lesson videos, it still has a few inherent limitations, which we have listed down below in these three bullet points of the text. And so to answer this original question, the reason that we need the lymphatic system is because, as we'll learn more about moving forward in our course, it functionally serves to address, accommodate, and provide a solution to each of these inherent limitations of the cardiovascular system. So that's important to keep in mind as we move forward in our course. And so what are these inherent limitations of the cardiovascular system anyways? Well, recall from previous lesson videos that the cardiovascular system is a relatively high-pressure system because of the action of the heart, which is constantly pumping blood through it. And this high pressure is a good thing because it allows for the high-speed transport and the rapid delivery of oxygen and nutrients to our tissues. However, this same high pressure and high-speed transport are also inherent limitations of the cardiovascular system, because the high pressure forces some fluids and proteins to leak out of the blood capillaries. And, of course, the leakage of its contents is not going to be a good thing. And although that high pressure allows for high-speed transport, the high-speed transport does not facilitate direct interactions between immune cells and pathogens, and so the high-speed transport does not optimize immune interactions, and again, that's a limitation. And then last but not least, for the most part, the cardiovascular system is not effective at absorbing relatively large macromolecules and substances, such as fats, for example. And so again, the lymphatic system is going to be needed because it is going to function to address many of these limitations. And so notice over here, we're showing you a person, and we're showing you these greenish, lymphatic vessels branching throughout, you know, practically this person's entire body, and there's also lymphoid organs that you can see that we'll talk more about moving forward, such as the thymus, the spleen, and tonsils, for example. Now over here on the left, what we're showing you is a typical capillary bed of the cardiovascular system, just like what you've seen before in some of our previous lesson videos. But what you'll notice is different here is that we're showing you these yellow cells here, which represent tissue cells, and, of course, we know that the capillaries is where exchanges occur between the blood and the tissues. But what you'll notice is really different about this image is that we're showing you all of these blue arrows, and some of the blue arrows are outward pointing and other blue arrows are inward pointing. Now the blue arrows that are outward pointing represent the leakage of fluids and proteins from the cardiovascular system, and what you'll notice is that these outward going arrows are broader and thicker than the inward going arrows, which represent the reabsorption of those leaked fluids and proteins. And so what this means is that over time, the cardiovascular system is leaking more of its contents than it is reabsorbing it back in. And so, again, the leakage is going to be something that is a limitation. But what you'll notice is that branching in over here is a little green vessel, which is a lymphatic vessel, and it is going to serve to accommodate that limitation. And so, again, that is why we need the lymphatic system. So as we move forward in our course, we'll get to talk more about what the lymphatic system is and its function. So that concludes our brief introduction of why we need it, and I'll see you on our next video.