Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson today on the cardiovascular system overview. Today we will be discussing the purpose and the structure of the cardiovascular system. The purpose of the cardiovascular system is to move blood throughout the body. Blood provides our tissues with oxygen and other necessary materials and it also aids in the removal of CO2. It's necessary that blood circulates through our body. In order to circulate that blood through our body, we have our cardiovascular system to do that for us, and the cardiovascular system is also sometimes called the circulatory system. So you may hear it either way. The cardiovascular system is composed of the heart and blood vessels. The heart is a muscular pump that pumps blood throughout the body. And blood vessels are tubes that transport the blood that's pumped by the heart.
There are actually various types of blood vessels. Blood vessels are just kind of a generic term to describe these tubes that transport blood. But there's actually various types of blood vessels that vary in their size, structure, and a little bit in their function. The types of blood vessels we have in our body are arteries, arterioles, capillaries, venules, and veins. We're going to use this diagram here to discuss these different types of blood vessels.
First of all, we have our heart here in our diagram. And when blood is flowing away from our heart it is flowing through arteries. Arteries are a type of blood vessel that carry blood away from the heart and they have a large diameter. This would be an example. This is just a very simple diagram of what an artery structure might look like. It's moving blood away from the heart.
Arterioles are similar to arteries in the fact that they also carry blood away from the heart, but arterioles are smaller in diameter. So up here we have the larger diameter arteries carrying blood away from the heart, which then eventually branches into these smaller diameter arterioles. And then those are arterioles will eventually branch into even smaller diameter capillaries.
Capillaries are the smallest blood vessel in our body and they are where substances are allowed to defuse from the blood into tissues. They're very, very, very small diameter, very thin layer, one membrane, one cell layer in capillaries. And then capillaries from there will start to branch back into venules which have a small diameter and actually substances can still diffuse through venules as well. But they do have a larger diameter than capillaries. So venules are actually starting to transport blood back to the heart. Arteries and arterioles are transferring blood away from the heart and venules are beginning to transport blood back to the heart. And
Then we get into veins. And veins have a larger diameter than venules. And the purpose again of veins is to transfer blood back to the heart. So these are our five different types of blood vessels. This lesson has been an overview on the cardiovascular system.
Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson on blood vessels. In this lesson today, we will be classifying the various types of blood vessels depending on their structure and their function.
So to start off, we're just going to basically define what a blood vessel is in general. So blood vessels are just tubes that transport blood. And blood vessels have an important role in our body because they can help manage our blood flow and our blood pressure with a contraction or relaxation of the smooth muscles that surround them.
So there are various types of blood vessels within our body. And we're going to be discussing those today. So to start out, we're going to take a look at this diagram right here. And we're going to use this to explain the different types of blood vessels found within our body. So I'm actually going to zoom in just a little bit to make this diagram a little larger.
So we have our heart labeled here in the middle. And we have a couple of different types of blood vessels that carry blood away from our heart. And we have a couple of different types of blood vessels that return blood to our heart.
So one of the types of blood vessels that carries blood away from our heart are arteries. So an artery is a blood vessel that carries blood away from our heart. And it has a large diameter. So arteries are made up of several layers, which include a layer of connective tissue, some smooth muscle, which, again, can contract or relax to manage blood flow and pressure. And it also has a layer of endothelium.
So arteries can pump high pressure blood from the heart. And they also have these stretchable walls, which offers little resistance to blood flow. So therefore, within arteries there's usually a stable pressure.
And if you've ever taken your pulse before-- if you've ever went for a jog or exercised and then measured your pulse afterward, what you're actually measuring-- or what you're actually feeling is the pressure surge in arteries when the ventricles within your heart contract. So you can feel your pulse at different parts of your body-- on your wrist, by your carotid artery near your neck. So you're feeling that surge of pressure when your ventricles contract. So arteries are a type of large blood vessel that carries blood away from the heart.
Our next type of vessel that carries blood away from the heart is arterioles. So an arteriole branches-- or an artery will branch-- I'm sorry-- into a narrower arteriole. So we start with arteries that have a large diameter, and they branch into these arterioles, which have a smaller or narrower diameter.
And arterioles are made up of a couple different layers, as well. And this includes a layer of smooth muscle and a layer of endothelium. So arterioles can dilate or constrict, again, because of that smooth muscle. So that smooth muscle can contract or relax, allowing the arteriole to dilate or constrict. And arterioles offer a little bit more resistance to blood flow than arteries.
Our next type of blood vessel are capillaries. So our arterioles will branch into these even smaller capillaries. And capillaries are tiny vessels that are found in capillary beds, which is basically like an interlacing network of capillaries.
So they're composed of just one thin layer of endothelium. And this allows for substances to easily diffuse between blood and tissues, because this one layer of endothelium is very thin. So diffusion occurs very easily.
So blood moves very slowly in capillaries. It actually moves very, very slowly in capillaries. But because of the amount of capillaries in our body they offer less resistance to blood flow than arterioles.
So capillaries branch all over throughout our body. And we have-- if you were to do, like, the amount of capillaries we have compared to any other vessel, we have the most capillaries. So because we have so many of them there's less resistance to flow than some of our other vessels.
Our next type of blood vessel are venules. So venules, now, capillaries will start to move blood back into venules. And venules start to return blood back to the heart. So capillaries will merge with these venules.
But venules also have thin walls. So because of the thin walls of venules, some substances can still continue to diffuse across in venules, as well. So diffusion is not just happening in capillaries. This is where most of our diffusion occurs. But a little bit of diffusion can also occur in venules, as well, as blood is starting to be returned to the heart.
And then we have, finally, veins. So veins have a larger diameter than venules. So we have the small diameter venules, and then we're going up into a larger diameter with veins. So veins, as I mentioned, have larger diameter. They have low resistance.
But a unique thing about veins compared to some of our other vessels is that veins actually have these valves that prevent backflow. So I'm now going to move to this diagram right here, because this diagram deals specifically with veins. So this is a diagram of a vein.
So it has this layer of connective tissue, smooth muscle, endothelium, and then it also has this valve here. So because we're going against gravity, veins have these valves that prevent backflow. So blood can flow through the vein, but it can't flow back. It's a one-way direction that blood can flow in these veins.
So the contraction of the smooth muscle equals stiffer walls of the vein, which equals a rise in pressure, which equals more blood flow to the heart. So these smooth muscles, as I mentioned, play a large role in managing blood flow and pressure. So when you're exercising, for example, those smooth muscles will contract. And then, as I said, that will cause the walls of the blood vessels to stiffen. Blood pressure will rise. And then more blood will be delivered to your heart more quickly.
So again, one more time, our overview of blood vessels. We have arteries and arterioles, which deliver blood away from the heart to the tissues. Capillaries act as an area of diffusion. And then venules and veins will return de-oxygenated blood back to the heart. So this lesson has been an overview on blood vessels.