Arteriosclerosis, arteriolosclerosis, and atherosclerosis

So there are a few words that get thrown around, and when I was going through and learning them, I was always confused. And so I thought I'd go and talk about them right now. The first word is arteriosclerosis. And I'm going to underline the one "o" here. And very similar to this word, there's the word arteriolosclerosis, with an extra "l" and "o", and everything else is the same. The first thing I always wondered was, are these the same word that someone just misspelled? But actually that's not the case. This is two separate words for two separate things. And the third word is atherosclerosis. I always used to wonder the same thing about this word. It was just like, is this just another way to spell it? Maybe the British spelling or something like that? But actually it's another word that's different in meaning as well. So these three words often get confused for one another. And sometimes you'll even see that they are referred to as the same thing. But there are some subtle differences that I want to talk about. So let's start with the first two words arterio- and arteriolosclerosis. And these basically get to the question, answering the question, of What? What is happening? And the process of arteriosclerosis and arteriolosclerosis is that you basically have stiffening of blood vessels. So if you have, let's say, a normal vessel-- I'll draw it in red-- like a little rubber hose, this is a very soft, flexible vessel. And over time, if it becomes stiff, like a lead pipe, then you have something like this, a very firm vessel. So the same size, but basically the walls are becoming very, very stiff. And arteriolosclerosis is kind of the same process. And so, so far I have not convinced you that there's any difference, right? Same basic process. So you're probably left wondering, well, then what is the difference? I'm going to firm. Well, the difference is that arteriosclerosis is happening in the large arteries and middle sized arteries. And remember we divided up the arteries into large and middle. And on the other side, we said, what about the small arteries and arterials? And that's over here. So basically, if this process is happening in the large or middle arteries, we would call it arteriosclerosis with a single "o." But if it's happening in the small arteries and arterials, we would call the same process arteriolosclerosis. So that's the key difference, right? Where is it happening? Now in terms of answering the question of what, this is the process. But you have to ask yourself, why does that matter? Why does it matter if something's going from soft to firm? Now, I'm going to draw a little spectrum for you, and on this side, we have the word "not," and here you have "very." And these are referring to compliance. So try to remember back to what we said about compliance. And that's whether or not a vessel can stretch, almost like stretchability. And if you think about what would be very stretchable, or very compliant, we've got veins. So that would be over here, a vein. Very compliant, right? And arteries are over here. They're not so compliant. They're not completely stiff, but compared to veins, they're not very compliant. So they have a much lower compliance than veins. And a lead pipe would be right here, basically right next to "not." This would be a lead pipe, right? And so when we talk about arteriosclerosis or arteriolosclerosis as something that's soft going into something that's firm, we're really talking about the artery moving from where it is on the compliance spectrum over here, towards not too compliant at all. So really we're talking about losing compliance. Let me write that-- losing compliance. That's really important. And that's really what we're talking about. Losing compliance. Now, how do we get to a point where we're losing compliance? How does that happen, exactly? Well, that's another question. That's the question of how, how does this happen? And there we can talk about atherosclerosis. So atherosclerosis is a process, and that-- I can even draw it out for you very quickly. This is, let's say, a blood vessel, an artery. And I'll draw two layers for its wall, although we know that there's actually three layers. Just to make it simple. I'm just drawing two layers just to show you there's a thickness. And let's say that you have some fat deposit here, and maybe one over here. And over time, we know that this is going to cause some blockage of the vessel. But also, in addition to losing space in the lumen-- this is the lumen-- in addition to losing space in the lumen, you also have some calcification, and some fibrous tissue starts kind of laying down here. So this wall, instead of being nice and soft and red, I'm going to draw it as very firm and white. Very firm. So this part of the wall, and maybe even this part of the wall, become very non-compliant. They lose compliance here. So these parts of the walls are very firm. They're not going to stretch out very easily. So that's atherosclerosis. And the reason I listed it under this section-- here, if I can divide it in half-- is that most often, not always, but most often, atherosclerosis is happening in the larger or middle sized arteries. It doesn't happen as often in the small arteries and arterials. So it's happening more often in the large and middle arteries, and so it's going to cause arteriosclerosis. So atherosclerosis is the "how," and arteriosclerosis is the "what" for the large and middle sized arteries. Now let's shift over to the small arteries and arterials. So, if I just told you that atherosclerosis doesn't happen too often in the small arteries, well then, how in the world does arteriolosclerosis happen? Again, arteriolo, with an "olo." How does that happen? OK. Let me write out for you a couple words. These are words that you might come across-- hyaline and hyperplastic. So, these are just names for a process. So these are, again, these are answering the question of "how" does arteriolosclerosis happen? Well, it happens through hyaline or hyperplastic arteriolosclerosis, so the word appears again here. And this-- let me just draw it for you like I did before. We have a vessel. Instead of having a plaque, which is what I drew before, in my vessel, this time I'm going to talk about blood pressure being really high. So here we're talking about things like, let me write over here, high blood pressure or, I'd say, diabetes. So in situations like this, you can have lots and lots of pressure pushing out of the vessel. This is my little arrows talking about blood pressure. And as the pressure is pushing out, what happens is that some of the proteins from inside of the vessel-- let's say you have some protein in here-- get pushed out. They're pushed out into the vessel walls. And that vessel wall gets loaded with protein, now, extra protein that doesn't usually belong there. And it's got little protein everywhere, because it's being pushed out by all that high pressure. And over time, having all this protein here-- I'm drawing in pink-- is going to cause these vessels to start losing compliance. So all the way around, actually. They start losing compliance. And again, this is not how it always happens, but this is just an example of how it could happen. You could lose compliance this way. So this would be an example of how something that was soft is becoming very firm over time because of blood pressure related issues. All right, we'll pick up there next time.