1 00:00:02,416 --> 00:00:06,544 Let's talk about blood vessels 2 00:00:06,544 --> 00:00:10,964 I'm going to talk to you about the different types of blood vessels that there are 3 00:00:10,964 --> 00:00:13,616 and we're going to see if we can come up with some general patterns. 4 00:00:13,616 --> 00:00:18,165 So let's start with the uh- let's say we take the blood vessel out of your body 5 00:00:18,165 --> 00:00:21,182 and examine it under a microscope. 6 00:00:21,182 --> 00:00:25,409 It would look something like this, where you have the middle: called the lumen. 7 00:00:25,409 --> 00:00:28,984 and right outside of the lumen you have cells. 8 00:00:28,984 --> 00:00:32,259 And these cells are going all the way around the lumen 9 00:00:32,259 --> 00:00:37,664 and they're the first type of cell that any blood would interact with, right? 10 00:00:37,664 --> 00:00:41,330 Because that's right immediately outside of the lumen. 11 00:00:41,330 --> 00:00:45,780 And on the other side of the cells, on the back side of the cells-if you think of the lumen as the front side- 12 00:00:45,780 --> 00:00:53,581 is a little line I'm gonna draw here to represent protein that sits there and 13 00:00:53,581 --> 00:00:58,962 acts as a scaffold, kind of like keeping all of the cells in place. 14 00:00:58,962 --> 00:01:05,660 So you have all of these endothelial cells. 15 00:01:05,660 --> 00:01:13,617 And then you have that little basement membrane- like a thin line of membrane- called the basement membrane 16 00:01:13,617 --> 00:01:17,731 And that keeps everything from falling out of place. 17 00:01:17,731 --> 00:01:21,651 And the thing that's in the basement membrane is mostly protein. 18 00:01:21,651 --> 00:01:24,215 So think about thinks like collagen which you can find 19 00:01:24,215 --> 00:01:28,015 in bones and your gums. That same protein is actually 20 00:01:28,015 --> 00:01:33,318 lining all of these blood vessels that are in your body. 21 00:01:33,318 --> 00:01:38,212 And together the basement membrane and endothelial cells, they make up a layer 22 00:01:38,212 --> 00:01:46,916 called the Tunica Intima. 23 00:01:46,916 --> 00:01:52,227 And that's kind of the word we use because "tunica" comes from the word for coat or cloak. 24 00:01:52,227 --> 00:01:56,715 And "intima" is kind of the intimate layer, the intimate coating of the vessels 25 00:01:56,715 --> 00:01:59,515 So Tunica Intima. 26 00:01:59,515 --> 00:02:05,114 Now right outside of this is another layer- and I'm gonna draw that right out here in red. 27 00:02:05,114 --> 00:02:08,529 And this will be a layer of muscle. Image these little lines 28 00:02:08,529 --> 00:02:13,533 represent smooth muscle cells. So this would be muscle and 29 00:02:13,533 --> 00:02:21,280 this would be the layer called tunica media, or middle. 30 00:02:21,280 --> 00:02:28,815 And the most important thing here is that there is smooth muscle in this layer. 31 00:02:28,815 --> 00:02:33,148 And finally, on the very outside, you have another layer. 32 00:02:33,148 --> 00:02:36,232 And I'm gonna draw it as a yellow line. 33 00:02:36,232 --> 00:02:41,482 And this yellow line represents more protein. This is another layer of protein, 34 00:02:41,482 --> 00:02:45,964 just like the basement membrane, but different composition of proteins. 35 00:02:45,964 --> 00:02:50,867 But again you see actually a lot of collagen, just as before, and some other proteins as well. 36 00:02:50,867 --> 00:02:57,666 And this is called the tunica externa. For external layer. 37 00:02:57,666 --> 00:03:05,422 Actually another word that they sometimes use for this is called "Adventitia." So you might see that word too. 38 00:03:05,422 --> 00:03:13,055 And the really interesting thing about the tunica externa is that you actually, on the large vessels, 39 00:03:13,055 --> 00:03:19,021 you find that they need blood to supply themselves, so some of these large vessels have little 40 00:03:19,021 --> 00:03:24,164 blood vessels on them. And you might think- well does this just go on endlessly? 41 00:03:24,164 --> 00:03:30,531 Ya know, vessels that have vessels on them and those little vessels have vessels on them and so on and so forth. 42 00:03:30,531 --> 00:03:38,972 Actually No. It's just the large vessels that have this. So you SOMETIMES, not always, 43 00:03:38,972 --> 00:03:45,407 see what's called vasa vasorum. And this is kind of a fancy name for it. 44 00:03:45,407 --> 00:03:49,665 But they're little blood vessels on blood vessels. Which I always thought was 45 00:03:49,665 --> 00:03:53,654 kind of a cool thing. So the tunica externa has the blood vessels 46 00:03:53,654 --> 00:04:00,276 and it also has nerve endings. And I'm not going to actually draw that in because it'd be 47 00:04:00,276 --> 00:04:11,786 kind of hard to show that. But nerve endings actually can be in that layer. In that tunica externa layer. 48 00:04:11,786 --> 00:04:15,243 So you've got three layers, each of them has some pretty cool things in them. 49 00:04:15,243 --> 00:04:21,749 And now what I thought we'd do is we'd go and think about each vessel type, and how this could look for that vessel. 50 00:04:21,749 --> 00:04:27,038 So let's start with the veins. And I'll do the veins over here. 51 00:04:27,038 --> 00:04:35,986 So let's say you have a vein. On the inside it has that tunica intima layer -and I'm not going to draw all of the 52 00:04:35,986 --> 00:04:43,243 cells out because now you know what that represents. That purple line represents the endothelial cells AND the basement membrane. 53 00:04:43,243 --> 00:04:51,076 And you also have a smooth muscle layer- so kind of a red line to represent tunica media. 54 00:04:51,076 --> 00:04:56,777 And veins have a tunica externa- a third layer. 55 00:04:56,777 --> 00:05:01,476 So veins kind of follow this general pattern. They have three layers and they're pretty straight forward in 56 00:05:01,476 --> 00:05:06,943 following exactly what I just talked about. 57 00:05:06,943 --> 00:05:15,107 Now arteries. Let me do a different color for arteries. Let's say red. 58 00:05:15,107 --> 00:05:34,101 I think of arteries in two different groups. So I think of large and middle sized arteries a little differently than I think about small arteries or arterioles. 59 00:05:34,101 --> 00:05:38,993 And you'll see that the small arteries and arterioles actually look quite similar to one another. 60 00:05:38,993 --> 00:05:42,483 So let's start with the large and middle sized arteries. 61 00:05:42,483 --> 00:05:52,157 So there you have, let's say, an inside. And then on the outside of that, on the tunica media layer- 62 00:05:52,157 --> 00:06:00,454 you start seeing a difference from the vein. You see that it's much larger, much larger. 63 00:06:00,454 --> 00:06:07,562 And in the vein you just had kind of a thin layer of smooth muscle, here you have a nice large layer of smooth muscle. 64 00:06:07,562 --> 00:06:13,543 And in addition to having these smooth muscle cells in the large and middle arteries you have an interesting 65 00:06:13,543 --> 00:06:24,023 new thing. You have something called elastin protein. And elastin is gonna be in here and this is a protein that 66 00:06:24,023 --> 00:06:31,560 helps make these very elastic. Right because they're going to have such high pressures that 67 00:06:31,560 --> 00:06:37,160 they have to be able to not break when these pressures are going through. 68 00:06:37,160 --> 00:06:59,287 So this elastin (this green elastin protein) helps make the arteries more elastic. More elastic for high pressures. 69 00:06:59,287 --> 00:07:01,029 And I'll write "P" for pressures. 70 00:07:01,029 --> 00:07:06,558 So that's what the middle layer looks like. And of course you still have your outer layer as before. 71 00:07:06,558 --> 00:07:14,077 So you've seen one key difference now with these large and middle sized arteries. 72 00:07:14,077 --> 00:07:18,012 Okay so now let's go to the small arteries and the arterioles. 73 00:07:18,012 --> 00:07:23,994 So here let's start out with the lumen, has that as before. 74 00:07:23,994 --> 00:07:28,313 And you also have a large tunica media. 75 00:07:28,313 --> 00:07:34,627 So unlike the vein, the tunica media in the arteries-in both types of arteries- is actually quite large. 76 00:07:34,627 --> 00:07:45,060 Except here, instead of having elastin in this area, you have just tons and tons of muscle. 77 00:07:45,060 --> 00:07:53,735 Lots of muscle. So they're very very strong in the sense that you can actually very easily squeeze down on the lumen 78 00:07:53,735 --> 00:07:57,917 if you wanted to by having all of this muscle contract. 79 00:07:57,917 --> 00:08:03,565 And that makes sense because we know that the arterioles - look at all of that muscle- the arterioles are actually 80 00:08:03,565 --> 00:08:17,043 going to be the ones that are going to create resistance. So here you have a lot of muscle. 81 00:08:17,043 --> 00:08:22,579 And this is to help create lots of resistance. If you need it, to change your blood pressures. 82 00:08:22,579 --> 00:08:29,465 So that's why the small arteries and arterioles are really helpful in squeezing down and changing blood pressures. 83 00:08:29,465 --> 00:08:36,015 And on the outside, they as before, have that layer of tunica externa. 84 00:08:36,015 --> 00:08:45,700 And this again is where the nerve endings go,and where the blood vessels, or the vasa vasorum go. So that's where that layer is. 85 00:08:45,700 --> 00:08:53,869 Okay. And you might be thinking there's gotta be one more vessel type and there is- 86 00:08:53,869 --> 00:09:01,719 and that's the capillary. So let me draw the capillary, so I'll do that over here. 87 00:09:01,719 --> 00:09:08,295 The capillary is actually going to look different from all of this other stuff that we've done because the capillaries 88 00:09:08,295 --> 00:09:22,950 are actually really really unique in the sense that-unlike what we had for the veins and arteries- this is down to the single cell level. 89 00:09:22,950 --> 00:09:28,232 So you still have a lumen but on the outside, instead of having a lot of endothelial cells 90 00:09:28,232 --> 00:09:38,697 you actually have, at times, one cell. One cell will actually form the entire wall of the tube. 91 00:09:38,697 --> 00:09:44,000 So you actually a cell travelling within a cell. Almost like the cell is giving the little red blood cell 92 00:09:44,000 --> 00:09:47,054 floating through it a big hug or something like that. 93 00:09:47,054 --> 00:09:52,351 So that capillary looks actually quite different as you can see from the other things that we've drawn: the veins and arteries. 94 00:09:52,351 --> 00:09:57,821 But I want you to just take a look at this again and see the key differences between the veins and arteries. 95 00:09:57,821 --> 00:10:04,530 The vein follows the general pattern. But the large and middle arteries have a lot of elastin in the tunica media. 96 00:10:04,530 --> 00:10:08,530 And the small arteries and arterioles have a lot of muscle in that tunica media.