General Blood Vessel Structure - Video Tutorials & Practice Problems
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concept
General Blood Vessel Structure
Video duration:
14m
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In this video, we're going to begin our lesson on the general blood vessel structure. And behind me is our lesson worksheet and we're going to break this lesson down one step at a time, starting off with this section that you can see boxed in red at the top. So let's zoom in and get started. So over here on the left hand side, we're showing you an image of the general blood vessel structure and notice that the layers are all peeled back so that you can see the components more clearly. And over here on the right hand side of the image, we're showing you a transverse cross section of the same image of the general blood vessel structure. And so moving forward in this video, we'll be utilizing both of these images to help you better understand the general blood vessel structure. And so before we continue, it's important to note that there are some structural variations amongst blood vessels. And so for example, there are some structural variations amongst the different types of arteries that we'll get to talk more about moving forward in our course in a separate video. And there are also some structural variations amongst arteries as a whole, capillaries and veins. And so moving forward in our course, separate videos, we'll get to talk more details about those structural variations. But for now in this video, what we can say is that although there are some structural variations, many blood vessels, especially the arteries as a whole and the veins as a whole are made up of three distinct structural layers or three distinct structural tunics. And so, moving forward in this video, we're going to be color coding each of these two images in order to highlight the components of each of these tunics. And so these three distinct structural tunics are the tunica intima, the tunica media and the tunica exter. And so let's shrink these images down a little bit so that we can make some room for our lesson text. And we're going to focus on each of these three tunics, one by one starting with the tunica intima. Now, the tunica intima as its name kind of implies is the internal or the innermost layer or tunic that is an intimate contact or direct contact with the blood that flows through the blood vessel. And so the tunica intima can contain three components which you'll see labeled down below in both of these images. And these three components are the endothelium, the sub endothelium and the internal elastic lamina. Now, the endothelium is a layer of simple squamous epithelium or a single layer of these squished or flat epithelial cells that lines the lumen of all blood vessels. And so this is an area where there is no structural variation amongst blood vessels. Since again, all blood vessels have an endothelium. And this endothelium creates a relatively slick, smooth and flat surface that minimizes friction with the blood that passes over it. And the endothelium is actually a continuation of the endocardium which recall from previous lesson videos is the epithelial tissue that lines the heart. And so the endocardium will actually extend outwards from the heart as the endothelium in order to line the lumens of all blood vessels. Now, functionally, endothelium has several different functions including physically affecting the blood flow since it's in direct contact with the blood, but also the endothelium can secrete chemicals that affect physiological activities such as vasoconstriction and vasodilation of some blood vessels. And also as we'll learn, moving forward in our course, when we discuss capillaries. In more detail, the endothelium plays an important role in the permeability of capillaries, which is going to allow for the exchange of substances between the blood and the surrounding tissues. Now, down below in the image on the left hand side, you can see the endothelium labeled here as this layer of simple squamous epithelium uh that lines the lumen. And over here on the right image, you can see the endothelium labeled as this layer right here. Now, next, what we have is the sub endothelium and the root sub is a root that means below. And so the sub endothelium is found immediately below the endothelium. And the sub endothelium consists of two components. The first component is the basement membrane which recall from previous lesson videos is a extracellular layer that is found immediately beneath of almost all epithelial tissue. And the second part of the sub endothelium is the loose connective tissue, uh mainly areolar, loose connective tissue. And so this areolar or loose connective tissue can help to bind or attach the endothelium to the rest of the blood vessel wall. And it can also help to facilitate diffusion through that layer of areola, loose connective tissue. And also recall that areola or loose connective tissue can harbor immune cells. And so uh this loose connective tissue can actually aid in the immunity of the blood vessel wall itself. Now, down below, in the image on the left hand side, you can see the basement membrane labeled as this light blue layer immediately beneath of the endothelium. And then you can see the loose connective tissue is this uh talish turquoise color here. Uh and that is going to be the areolar loose connective tissue. And over here, on the right hand side of the image you can see again, the basement membrane is this light blue color right underneath of the endothelium. And then this other blue color that you can see separated by the dotted line is going to be the loose areolar connective tissue. Now, last but not least we have the internal elastic lamina, which can be abbreviated as IEL and sometimes it's also referred to as the internal elastic membrane. Now, as its name implies with the term elastic, this is going to be a layer of elastic connective tissue which recall contains lots of elastin proteins which allow for elasticity or the ability to stretch, but then also recoil back to the original shape. And so this internal elastic lamina is usually only going to be present in larger arteries that are relatively close to the heart and need to be uh able to have that elastic ability to stretch and recoil back. And uh the reason that these larger arteries need to be more elastic is because they are closer to the heart which generates forceful contractions and ejects blood out of the heart uh with relatively high pressures. And so these larger arteries need to be able to have this elastic ability in order to uh prevent damage to those vessels. Now, down below, in this image, on the left hand side, you can see the internal elastic lamina labeled as this yellow structure, that kind of looks like Swiss cheese. And that's because it actually does have holes in it that allows for improved diffusion and also allows for substances to penetrate more easily as well. And over here, on the right hand side of the image, you can see the internal elastic lamina labeled as this yellow structure that goes all the way around. And so this year concludes the tunica intima, so we can go ahead and check it off and we can move on to the next tunic, which is the tunica media. Now, the m in tunica media can remind us that this tunic is the middle tunic or the middle layer in between the tunica intima and the tunica external. And the tunica media is often going to be the thickest layer or the thickest tunic, especially in arteries. Now again, the M and tunica media can remind us that this layer contains mostly smooth muscle. And so notice down below in the image, we've got the smooth muscle labeled on the left hand side as this relatively thick layer in pink. And on the right hand side, you can see the smooth muscle of the tunica media and as this thick layer in pink as well. Now, in addition to the smooth muscle, the tunica media may also contain some elastic fibers, especially in the arteries that are closer to the heart. In fact, the tunica media may contain an external elastic lamina or an eel, which is sometimes also referred to as an external elastic membrane. And this is really similar to the internal elastic lamina that we discussed earlier in this video. But the main difference is that as its name implies with the term external, it's going to be closer to the exterior surface in comparison to the internal elastic lamina. And again, it's going to be found mainly in the larger arteries that are closer to the heart that need to be able to have the elastic ability to stretch, but then recoil back to its original shape. So notice down below in the image, we have the external elastic lamina labeled as this Swiss cheese looking structure here in yellow that have these holes to allow for substances to diffuse and penetrate more easily. And over here on the right hand side, we are labeling the external elastic lamina as this structure in yellow, that is relatively close to the exterior surface. And the external elastic lamina will actually separate the tunica media from the tunica external when it is present. Now, the smooth muscle of the tunica media will actually contract or it contracts in order to allow for vasoconstriction, the narrowing of the diameter of the blood vessels and the smooth muscle actually relaxes to allow for vasodilation or the enlargement of the diameter of the blood vessels. And so the smooth muscle of the tunica media is critically important for the regulation of blood flow and blood pressure throughout the entire cardiovascular system. And again, it's the arteries that usually contain larger thicker tunica medias with more smooth muscle. And so it's the arteries that have greater ability to uh vasoconstrict and vasodilate. And so this year concludes our lesson on the tunica media. So let's move on to the last tunic which is the tunica external. Now, the tunica ex terna is also sometimes referred to as the adventitia. And as its name implies, the tunica exter is the external or the outermost layer or tunic. And it's actually composed mostly of collagen fibers. And these collagen fibers are either of loose connective tissues or dense irregular connective tissue, depending on the type of blood vessel and depending on the location of the blood vessel within the body. And so these collagen fibers help to provide structural support uh to that tunica external and to the blood vessel. Now, down below, in the image, you can see that we're labeling the collagen fibers in both images. Now, what's really important to note is that the internal layers and tissues of the blood vessel wall that are closer to the lumen of the blood vessel will actually receive their nutrients directly from the blood that passes through the lumen. However, those nutrients will only diffuse so far toward the external tissues of the blood vessel wall. And so the exterior parts and exterior tissues of the blood vessel wall also need to be nourished. And so this is where the vasa varum comes into play. And this is a system of tiny blood vessels that actually nourish the external tissues of the blood vessel wall. And so notice that in the image on the left hand side, we're labeling the vasa varum as these red circles and also these blue circles and you can see them extending upward here. These are the tiny blood vessels of the vasa varum that help to nourish the blood vessel walls on the exterior parts. And you can also see the vasa vm labeled on the right hand side of the image as well as these blue and red dots. Now, in addition to the collagen fibers and the vasa varum, the tunica external can also have nerves and lymphatic vessels and even elastic fibers as well, especially in the larger arteries that are closer to the heart. And so notice that we're actually showing you some nerves here in yellow and that can help stimulate the smooth muscle to contract. Now, the tunica external is going to be important for protecting and reinforcing the blood vessels again, because it has those collagen fibers that can provide support and also the tunica e external is important for anchoring the blood vessel to its surrounding tissues. And so that concludes our lesson on the tunica exter. And so now we've covered all three tunics and we are basically done with the general blood vessel structure. So here are all of the labels and you can see them all labeled here in both images. So that concludes this video and moving forward, 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.
2
example
General Blood Vessel Structure Example 1
Video duration:
4m
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So here we have an example problem that says to appropriately label each image with the tunic that it is highlighting and list the components of each tunic. And so notice down below, we've got these three images of the blood vessel structure and notice that each image is highlighting a specific tunic. And so the image on the far left is highlighting the innermost tunic that is on the inside here. And so this is going to be the tunica intima which recall is in intimate contact with the blood flowing through the lumen of the blood vessel. And recall the tunica intima includes the endothelium, which is the simple squamous epithelia that lines the lumens of all blood vessels. And and this image is shown in these areas that I'm indicating here. Uh It also includes the sub endothelium which recall is immediately beneath the endothelium since the root sub means below. And the sub endothelium includes both the basement membrane and loose connective tissue, mainly areolar connective tissue. And so no, no notice that the light blue that you can see in both images here represents the basement membrane. And then this teal turquoise type color that you see represents the loose connective tissue. Now, last but not least we have the internal elastic lamina, which I will abbreviate as Iel. And the internal elastic lamina is found mainly in the larger arteries that are closer to the heart. And it is going to allow for elasticity, the ability to stretch but also recoil back to its original shape. And so in this image over here, it's shown as this yellow Swiss cheese looking structure. It's got these holes that allow for diffusion and substances to pass through more eas easily. And uh in this image over here, it's shown as this yellow structure going around. Now, that's it for the tunica intima. The next image over here is highlighting the middle tunic which is going to be the tunica media and recall the tunica media has smooth muscle. And so notice that the smooth muscle in these images is being highlighted as these pink layers in both of these images here. Now, in addition to this uh smooth muscle of the tunica media, it may also contain an external elastic lamina which I will abbreviate as eel and the external elastic lamina is very similar to the internal elastic lamina, except it is going to be positioned more exteriorly in the wall of the blood vessel. And so you can see it here as this yellow structure in this image. And uh again, it's usually found in larger arteries that need elasticity. Now, last but not least over here on the far right. This image is highlighting the external tunic, which is the tunica external, which recall is also sometimes referred to as the adventitia. And uh it is going to consist mostly of collagen fibers. So we can put in collagen right here and recall that the innermost layers of the blood vessels are going to receive their nutrients from the blood that passes through the lumen. However, that those nutrients will not be able to diffuse to the exterior tissues in the exterior parts of the blood vessel. And so uh the exterior tissues need to be nourished with a vasa varum, which recall is a tiny system of uh it's a system of tiny blood vessels that uh feed and nourish the external tissues. And in addition to that, it may also have nerves and lymphatic vessels and also elastic fibers, especially in the arteries that are closer to the heart. And so this year concludes our example problem and I'll see you on our next video.
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Problem
Problem
Which of the following statements is true?
A
The tunica media in veins is thicker than tunica media in arteries.
B
The tunica intima contains the endothelium, which lines the lumen of all blood vessels.
C
The walls of all blood vessels always have 3 distinct layers/tunics.
D
The tunica externa is mostly composed of smooth muscle that can contract, causing vasoconstriction.
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Problem
Problem
Which blood vessel layer contains the greatest proportion of collagen?
A
Tunica intima.
B
Tunica media.
C
Tunica externa.
D
The elastic laminae.
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Problem
Problem
Which blood vessel tunic has the most active role in controlling blood flow?
A
Tunica intima, as it is makes direct contact with the blood.
B
Tunica media, as it contains smooth muscle which causes the vessel’s diameter to change.
C
Tunica externa, as it dampens the large pressure changes caused by the beating of the heart.
D
None of the layers play an active role in controlling blood flow.
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