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 a way. And so 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 external. 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 greater ability to change the size of their diameter via vasoconstriction or vasodilation in comparison to veins. And 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. And 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 and 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 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.
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concept
Subcategories of Arteries
Video duration:
14m
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In this video, we're going to begin our lesson on the subcategories of arteries. And notice behind me is our lesson worksheet and we're going to break this lesson down one step at a time starting with this section that you can see boxed in red at the top. So let's zoom in and get started. So recall that arteries are blood vessels that always carry blood away from the heart. And it turns out that there are three subcategories of arteries that are based on their size and their function. And these three subcategories of arteries are the elastic arteries which are the largest arteries that are closest to the heart. Then we have the muscular arteries which are medium sized arteries. And then last but not least we have the arterials, which we already know from previous lesson videos are the smallest of the arteries. And we also have an image for each of these corresponding arteries showing you the details of their wall structure. And so in this video, we're going to discuss each of these three subcategories of arteries starting with the elastic arteries. So again, these elastic arteries are the largest of the three subcategories of arteries with the largest diameter and they are located near the heart, which is why down below in the image, we're showing you an elastic artery with the largest diameter located near the heart. Now, in this box, over here, on the left hand side, we can label the title elastic arteries. And again, although these elastic arteries are the largest with the largest diameter, it's important to note that their wall thickness is relatively thin in comparison to their diameter. And you can kind of see that in this image down below. But if we zoom into the wall structure even more, what you'll notice is that we're labeling the lumen diameter as 15 millimeters, but we're only labeling the wall thickness as one millimeter. And of course, there's variation when it comes to the wall thickness and the lumen diameter of these elastic arteries. But what you can gather from this is that when it comes to these elastic arteries, usually their lumen diameter is far greater than their wall thickness. Now, these elastic arteries are also sometimes referred to as conducting arteries, which is why we have conducting in parentheses. And this is because these arteries will conduct or facilitate the movement of blood directly from the heart into the medium sized muscular arteries that we'll get to talk about here shortly. Now, these elastic arteries as their name implies with the term elastic, have lots and lots of elastin which recalls the protein that's found in elastic connective tissue. And all of this elastin makes these elastic arteries elastic, meaning that they have the ability to stretch significantly but also recoil back to their original shape after stretching. In fact, these elastic arteries have more elastin than any other type of blood vessel. And the elastin is distributed all throughout the wall of these elastic arteries in every tunic, including the tunica intima, the tunica media and the tunica turn up. However, it's the tunica media, the middle layer with the smooth muscle that contains the most amount of elastin, which is why we're showing you all of these yellow squiggly throughout the smooth muscle of the tunica media to represent all of that elastin in these elastic arteries. Now, these elastic arteries, although they do have smooth muscle, it's important to note that they are relatively inactive in terms of vasoconstriction and vasodilation. And so the smooth muscle was more so there for structural purposes rather than uh facilitating uh extreme amounts of vasoconstriction and vasodilation. The vasoconstriction and vasodilation is more so going to be a role of the muscular arteries and arterials. Now, these elastic arteries may actually have an internal and external elastic lamina, which recall from our previous lesson videos are these yellow structures that you can see I'm highlighting here and it's important to note that there's so much elastin in the walls of these elastic arteries that often these internal and external elastic lamina are difficult to distinguish under the microscope. And so sometimes these internal and external elastic lamina are not really considered to be there because they are just embedded within all of this elastic tissue present throughout the wall. Now, the elasticity of these elastic arteries is very important because it allows the walls of these elastic arteries to stretch significantly in order to hold blood from the heart contraction, which recall that the heart will contract forcefully to eject blood out of the heart into these arteries with relatively high blood pressures. And without stretching, these elastic arteries could become damaged uh in that case, but the stretching helps to uh accommodate the blood ejecting forcefully into these arteries. However, just as important as the stretching is the recoil that occurs during diastole or during the relaxation period of the heart. And so the recoil of these elastic arteries back to their original shape helps to keep the blood flowing continuously even when the heart is in its relaxation period. And that helps to prevent downstream pressure surges that could otherwise cause damage. Now, this here concludes our lesson on the elastic artery. So we can go ahead and check them off and move on to the next subcategory of artery, which is the muscular artery. So these muscular arteries are medium sized arteries with diameters that are smaller than elastic arteries, but larger than arterials. And these muscular arteries account for most of the main arteries that are named and studied in anatomy and physiology courses. And as their name implies, with the term muscular, these muscular arteries have lots of smooth muscle. They have more smooth muscle, then elastic arteries giving them greater ability for vasoconstriction and vasodilation. But they have less elastin than those elastic arteries, which means that they have less ability to stretch and recoil. However, these muscular arteries are further away from the heart. So they don't need that elasticity as much as the elastic arteries do from being closer to the heart. Now, these muscular arteries have so much smooth muscle that the smooth muscle accounts for about 75% of the mass of a muscular artery. So that's a lot of smooth muscle. And so if you take a look at the image down below, notice that there is quite a lot of smooth muscle in the tunica media and that's going to be the defining feature of these muscular arteries. Now, although they have less elastin than elastic arteries, they still can have some elastin. And so these external and internal elastic lamina may still be present and notice that the lumen diameter is being indicated as six millimeters and the wall thickness is being indicated as one millimeter. And so the wall thickness is about the same as the wall thickness of elastic arteries. But notice that the lumen diameter is smaller in muscular arteries than it is in elastic arteries. Now, these muscular arteries will receive blood from the elastic arteries and they will deliver or distribute the blood towards specific organs and muscles. And this is why muscular arteries are also sometimes referred to as distributing arteries because of their ability to distribute or deliver blood towards specific organs and muscles. Now this year concludes our lesson on muscular arteries. So we can go ahead and check these off and let's move on to the last subcategory of artery, which is the arterials. So we already know from previous lesson videos that arterials are the smallest of the arteries with the smallest diameters, but not only are they the smallest, they're also the most numerous of the arteries. In fact, it's estimated that there are hundreds of millions of arterials in the average human body in various locations. And most of these arterials are not named. So you don't need to worry about memorizing them. Now, these arterials are important for regulating blood flow directly into the capillaries. Now, later in our course, in a separate video, we'll talk more about the capillaries. But recall from previous lesson videos that the capillaries are important for the exchanges that occur between the blood and the surrounding tissues. Now, in this image over here, on the right hand side, you can see in this dotted box, we're highlighting the arterial, the smallest of the arteries and it's feeding blood directly into these capillaries where again the exchanges occur between the blood and the surrounding tissues. And that's indicated by this color change to purple. Now, the arterials actually vary in terms of their size and structure. And so the largest arterials will have all three tunics in their wall. However, those tunics are relatively thin and they contain more smooth muscle than Elastin giving them great their ability to vasoconstrict and making them not so elastic. Although arterials are quite far away from the contracting heart, so they don't really need to be as elastic as the larger arteries that are closer to the heart like the elastic arteries. Now, the smallest of the arterials are not much more than just the endothelium and a single layer of smooth muscle around them. Now, these arterials will actually vasoconstrict and play a huge role in increasing what's known as resistance throughout the cardiovascular system. Now, later in our course, we're going to talk more about this resistance. However, the resistance is any opposition to blood flow or in other words, it's a measure of how difficult it is for blood to flow through the blood vessels, the greater the resistance, the more difficult it is for blood to flow through. And ultimately, resistance is a measure of the amount of friction that the blood encounters with the walls of the blood vessel as the blood travels through the cardiovascular system. And so resistance is greatly impacted by the diameter of the blood vessels. And so vasoconstriction will increase the resistance. And because arterials are the smallest and the most numerous the vasoconstriction of the arterials has the greatest impact on resistance. And because that's the case, these arterials are also sometimes referred to as resistance arteries. Now, the vasoconstriction of these arterials can also redirect blood flow away from capillaries. In order to avoid exchanges in those capillaries and the redirection of blood flow can redirect blood to areas of the body that may have a greater demand for blood. Now, in this image down below, notice that we are zooming into the wall structure of this arterial and notice that the thickness of this wall is being indicated as 0.006 millimeters, which is quite small. It's the smallest thickness of the wall that we've seen so far and notice that the lumen diameter is being indicated as 0.037 millimeters. And again, there is variation in the wall thickness and lumen diameter. But in general, these arterials or resistance arteries are going to have significantly smaller lumens and significantly smaller wall thickness. And so this here concludes our lesson on the arterial, so we can go ahead and check them off. So now that we've covered the three subcategories of arteries, we're now going to talk about the size ranges of each of these three subcategories of arteries and compare them to regular household items that you may be more familiar with. And so recall that the elastic or conducting arteries are the largest of the arteries. And so they can be as large as about a garden hose and so their diameter can be as large as about 25 millimeters. And on the smaller side, they can be about the diameter of your pointer finger, which of course can vary but is about 10 millimeters. Now, anything smaller than 10 millimeters is starting to get into the range of muscular or distributing arteries which recall our medium sized arteries with lots of muscle and so on the larger end, these muscular arteries are about the diameter of a pencil which is about seven millimeters. And on the smaller side, they're about the diameter of a string which is about 0.3 millimeters. Now again, anything smaller than 0.3 millimeters is starting to get into the range of these arterials or resistance arteries, which recall are the smallest and the most numerous of the arteries. Now, on the larger side, these arterials are about the diameter of your hair, which is about 0.18 millimeters. And on the smaller side, these arterials are microscopic down to about 15 micrometers in diameter, which is why we have the microscope here. And so this year concludes our lesson on the subcategories of arteries and moving forward. In our course, we'll be able to apply these concepts and continue to learn more about blood vessels. So I'll see you all in our next video.
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example
Arteries Example 1
Video duration:
1m
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So here we have an example problem that says to label each of the diagrams below with their corresponding type of artery. So notice that we've got these three images and we need to label them either as elastic artery, muscular artery or arterial. Now, taking a look at this image on the far right. One thing that stands out to me is the vast amounts of smooth muscle that it has in its tunica media. And so this large amount of muscle, smooth muscle tells me that this is likely going to be a muscular artery. So we can label this image on the far right as option B in order to label it as muscular artery. And then we can cross off muscular arteries since we've already labeled it. Now, uh looking at this next the vessel that you can see here, notice that it is relatively thick in comparison to this next uh vessel wall. And so what that tells me is that this one in the middle must be the elastic artery, especially since it has the internal and external elastic lamina structures, those yellow layers within the wall here. So we can go ahead and label this middle structure as answer option A to label it as elastic artery. And then we can cross that off. And then of course, that means that this final image on the far left over here must be the arterial so we can label it as C so that concludes this example problem and I'll see you all in our next video.
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example
Arteries Example 2
Video duration:
1m
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So here we have an example problem that says to label each image below with the type of artery that corresponds best with the size or diameter of the item. And so notice that we've got these three items down below a pencil hair and a garden hose. And we need to label them either as elastic artery, muscular artery or arterial. And so of course, recall from our last lesson video that elastic arteries are going to be the largest of these three arteries with the largest diameter. And so notice of these three objects, it's going to be the garden hose that has the largest diameter. And so uh we, what we can do is we can label the garden hose as answer option A in order to label it as the elastic artery and then we can cross off option A. Now the pencil is going to have the next largest diameter and recall that muscular arteries are going to be the medium sized arteries. And so they are going to have the next largest diameter, which means that we can label this pencil as answer option B and then cross off option B since the muscular artery is being linked to the pencil. And then of course, last but not least the hair over here is going to be very, very thin with a very thin diameter. And so that's going to match up with the arterial, which we know is the smallest of the arteries and is going to have the smallest diameter. So we can label the hair as answer option C and that concludes its example. So I'll see you all in our next video.
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Problem
Problem
What is the protein-rich substance in elastic arteries that contributes to their ability to recoil & maintain blood pressure during diastole?
A
Collagen.
B
Elastin.
C
Smooth muscle.
D
Fibroblasts.
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Problem
Problem
Which type of artery has the thickest tunica media in proportion to the rest of its wall?