In this video, we're going to do a little bit more of a formal introduction to arteries. And so, recall from our previous lesson videos when we overviewed the major types of blood vessels, we already defined arteries as blood vessels that carry blood away from the heart. And so, recall that the 'a' in artery can remind you of the 'a' in away. And now for some new information. Structurally, the walls of arteries contain all three tunics or all three layers that we talked about in our previous lesson videos, including the tunica intima, the tunica media, and the tunica externa. However, it's actually the tunica media, the middle layer, that is especially thick in arteries in comparison to veins. And so, recall that the tunica media contains smooth muscle, and so having a thicker tunica media means that arteries have a greater ability to change the size of their diameter via vasoconstriction or vasodilation in comparison to veins.
Also, arteries have lumens that are generally smaller compared to the lumens of veins. And so, if you had a foot-long artery and a foot-long vein, the foot-long vein would be able to store a larger volume of blood because it has a larger diameter. Also, compared to veins, arteries are plentiful in elastic fibers, which is important because it allows arteries to easily expand and recoil. This is very important because arteries are found very close to the heart, which generates forceful contractions that ejects blood out of the heart with force. And so, there are high pressure surges in the arteries that are close to the heart. And so, it's very important for them to be able to expand, but also to recoil in order to accommodate those high pressure surges and make sure that those arteries are not damaged. So it's very important for arteries to have these elastic fibers.
Now veins are generally going to have lower pressure as we'll continue to learn moving forward in our course, and so they do not need to have as many elastic fibers since they don't need to accommodate these high pressure surges. And so, let's take a look at our image down below, which is pretty straightforward. On the left-hand side, what we have is the heart, and of course, we know that blood vessel, I'm sorry, arteries are blood vessels that carry blood away from the heart. So here's our heart, and notice right over here we have the artery. And notice that the blood flow through the artery is pointing away from the heart. And so, as we move forward in our course, we're going to be able to talk a lot more about arteries, including the subcategories of arteries, which we'll talk about in our next lesson video. So, I'll see you all there.