Cardiac Cycle - Video Tutorials & Practice Problems
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1
concept
Systole, Diastole, Pressure, & Valves
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7m
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We, I wanna talk some about the cardiac cycle and I'm just gonna start by defining that the cardiac cycle is this cycle of contraction and relaxation that moves blood through the heart. Now, at this point, you should know your structures of the heart. You should know the basic pathway that blood takes through the heart. What we want to talk about now is why blood takes that very specific one way path. And how does the contraction and relaxation change the pressure in the heart in a way that makes those one way valves open and close. Now, here we're gonna talk about it sort of very generally and just talk about pressure and valves in more general terms. And then we'll take what we learn and apply that to the four chambers of the heart and really see what's going on in that thing, beating in your chest. All right. So to start, remember, we're talking about contraction and relaxation, but this is anatomy and physiology. So we have fancy words for things we're gonna say systole is contraction and the way you use that word in a sentence, you would say that a particular chamber is insistently. Now, the way I remember what systole means is I have a little alliteration memory tool. Here, I say the systole squeeze. All right. So systole equals squeeze when the chamber is contracting, it's in systole and that squeezes inwards. Now, systole, we also have diastole diastole, therefore, is relaxation. And again, how you use diastole in a sentence, you would say a particular chamber is in diastole. Now, to remember this, we also have a little alliteration memory tool here, I say the diastole drop during diastole, the pressure drops because the chamber's relaxing. All right, we're talking about squeezing and relaxing and that's gonna change the pressure in the heart and it's gonna be the changes in this pressure. It's gonna force valves open and close whenever you're thinking about a valve, whether it's open and closed. You wanna think what is the pressure on one side of the valve compared to the pressure on the other side of the valve? And that's gonna push the valve in one direction or the other. Now, when you're thinking about that, we wanna say that the ventricles cause most of the pressure change in the heart. So sure, the atria go through Sicily and diastole, but it's the ventricles whose pressure changes are really important. Those are the big heavy parts of the heart and when they contract when they go into Sicily, that pressure changes dramatically. So while the atria and the ventricles both go into systole and diastole and they go through them at different times. We can even just say that the heart goes into systole or the heart goes into diastole. When we say that we're talking about the ventricles because for pressure changes, that's really what matters. Ok. Now, before we go on, we just wanna remind ourselves of the valves in the heart. For every ventricle, you have two ventricles and for each ventricle, there is an atrioventricular valve or an A V valve. And I think of that as the in valve to that ventricle, things go into the ventricle through that valve and that valve opens inwards into the ventricle. Now, we also have a semi lunar valve which we can abbreviate as an sl valve sometimes. Now the semi lunar valves for the ventricle, that's gonna be the out valve and importantly, it opens outwards. Now, to remember those we have this fun little made up word here. You can just shout out Evan Slough, Aven slough A VN things go into the ventricle through the A V valve and it opens into the ventricle sl out things go out of the ventricle through that semi lunar valve and it opens outwards. All right. Now, to think this through, we have a sort of simplified pump here representing a ventricle and our A V valves and semi lunar valves. So if you're following along on your printable PDF, you'll see that this is more in a comic book form here we're gonna look at an animation. So as we look at this, we have the A V valves over here on the left. Those are those valves that are pointing into the ventricle and we have the semi lunar valves here. Those are our out valves on the right. Those are the valves that open outwards away from the ventricle. And instead of showing something, the whole ventricle squeezing here, we have a simplified again pump system where we're gonna have a piston that goes up and down to change the pressure. All right. So let's think through what's gonna happen during systole and diastole of the ventricles. So, during ventricular systole, well, during cyst, we have the cysto squeeze. So you can probably guess what's gonna happen in the pressure as it contracts that pressure is going to go up. Now, let's think what that will do to the different valves. Well, we can watch our animation to see. So we're gonna see this piston push upwards. I just wanna pop it right there, stop it right there. We can see at this point we've increased the pressure enough that those indoors the A V valves are now shut. The pressure in the ventricle here on this side of the valve is greater than on the other side of the valve. So the doors are closed. So the first thing as that ventricular pressure rises, we're gonna see that the A V valve closes. All right, as we let this contract even more. It continues through Sicily. And we will see that that piston is gonna push up and up. And we can see now that, that semi Lunar valve, well, the semi lunar valve was pushed open, semi lunar valve opens because the pressure in this ventricle was higher than on the other side of that valve. And as the out valve, it opened outwards well as we keep it going here. Well, now we finished sly and now we go into diastole and diastole, the pressure dropped. So this piston is gonna come back down again. Well, as this goes, you can see the pressure drops, we're gonna put the arrow down there and I'll start this up. Well, we see right away the first thing that we see as that pressure drops, it's no longer putting pressure on that semi lunar valve. Now, there's some blood in this artery here that's pushing backwards. So now the pressure up here on this side of the valve is greater than the pressure in the ventricle. So that out valve that semi lunar valve closes. So the semi Lunar valve closes. And as we keep going here, this pressure continues to drop. And we can see now the A V valve opens the pressure on the top side of the A V valve, there is now greater than the pressure on the bottom. And I'll just keep this playing here. But here, I'm gonna say the A V valve opens and we can see it going. All right, pressure rises. A V valve close. Semi lunar valve opens as the pressure vol falls in diastole, the semi lunar valve closes and then the A V valve opens again as you follow this through. Always remember in which way does the valve open? And what is the pressure on either side of that valve? If you know those things, you know whether the valve is gonna be open and closed and you know which way blood can move through that valve. All right, we're gonna practice this more and practice problems. And again, then we will look at actually the four chambers of the heart and lay all this information on there, looking forward to it. I'll see you later.
2
example
Cardiac Cycle Example 1
Video duration:
6m
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Our example tells us that the opening and closing of heart valves is due to relative pressure in the ventricles compared to the atria and the arteries. We want to use our knowledge of heart anatomy to complete the following table. And in this table, we see the relative pressure between two different places in the heart. We see that a couple of times here and then we wanna know what is the valve that's gonna be affected by that relative pressure we're talking about is the valve open or closed and is the ventricle in Syle or diastole? All right. So far, we've just talked about sort of pressure changes generally. Now we're gonna go through all this and compare it to the heart. But even right now, you should know your heart anatomy decently well. And just knowing these pressure changes, you should be able to figure out what's going on here. So let's give it a try. So we're gonna start with the aorta. It says the aorta, the pressure in the aorta is greater than the pressure in the left ventricle. Well, here's our AORTA and here's our left ventricle. So the first question is what's the valve that's affected what valve is between the aorta and the left ventricle. Well, I'm gonna say that that's the left semi lunar valve. I'm just gonna write abbreviations there just to save space. Uh or slash, we can also call that the aortic valve, the aortic uh semi lunar valve. All right. So the left semi lunar valve or the aortic semi lunar valve. And so if the pressure is greater in the aorta than the left ventricle, is that valve gonna be open or closed? Well, if the pressure is greater up here, that means that it's sort of pushing backwards on there. And that's the opposite way that we want blood to flow, right? Those semi lunar valves, those are the outdoors for that ventricle. So if the blood is trying to sort of go in the opposite direction than it's supposed to go, that's gonna push that valve closed. So this means that the valve is gonna be closed. And next we want to know is the ventricle gonna be in systole or diastole? Remember we have the cysto squeeze, that's contraction, diastole, the pressure drops during relaxation. Now, just to be really clear for all of these, technically, it could be in either one and it will be in either one during sometimes during the the heart cycle. However, for most of the time, generally, we can say systole diastole for this. So if the pressure in the left ventricle is lower than the pressure in the aorta. Would you expect that that heart is in cystically or diastole? Well, if the pressure is low in the ventricle, that means that it is likely in diastole, that pressure is dropped, the pressure is fallen because the ventricle is relaxing. All right. Next up, we have the pressure in the right atrium is greater than the pressure in the right ventricle. So, here's our right atrium, here's our right ventricle. So, first off, what is the valve that we're talking about here? Well, I can call that the right A V valve or right ATRIO ventricular valve. And I'll just uh sort of write in the abbreviations there and we can also say sort of slash tricuspid if we want to use the other name, the tri cusp and is the valve gonna be open or closed? All right. Well, if the pressure is greater in the right atrium than in the right ventricle, so the pressure is greater here, that means it's sort of pushing this way. Well, that's the indoor to the ventricle. So if the pressure is greater on the other side, it's gonna push that indoor open and blood is gonna be flowing into the ventricle at this time. So this is gonna say that this valve will be open. And is that gonna happen when the ventricle is in Sicily or diastole? Well, again, here we see the right ventricle is in low pressure, it's gonna have low pressure here So low pressure typically happens during diastole, that pressure drop when the ventricles relax. All right. Next up, we have the pressure in the left atrium is less than the pressure in the left ventricle. So, here's our atrium, left atrium, here's our left ventricle. First off. What is the valve that's between them? Well, the valve between them would be the left A V valve again. I'll just use some abbreviations here to save some space. Slash. The mitral valve is the other name for it. And is that valve gonna be open or is it going to be closed? All right. Well, the pressure in the left atrium is low, the pressure in the ventricle is gonna be high. So that means that when this pressure is high in the ventricle, it's gonna be pushing back up this way, that's gonna slam those indoors, those A V valves shut. So we're gonna say here closed. And when does that happen? When is the pressure in the left ventricle higher than the pressure in the left atrium? Well, typically that happens when the ventricle is in cysto, that cyst squeeze, it's contracting. All right. Our final one here, we have the pressure in the pulmonary artery is less than the pressure in the right ventricle. All right. So here we have the pressure, here's our pulmonary artery, here's our right ventricle. All right. So what's the valve between them? What's that valve right there? What we're gonna say here? This, you could call the right semi lunar valve. You could also call it the pulmonary valve or the pulmonary semi lunar valve. All right. Now, if the pressure in the pulmonary artery is less than the pressure in the right ventricle is that valve gonna be open or closed? All right, the pressure here is low and the pressure here is high. That means that it's gonna be pushing in this direction. This is the outdoor to this ventricle. That means that that outdoor is gonna be pushed open. So the semi lunar valve will be open. And will that happen when the ventricle is in systole or diastole? Well, we have the pressure in the ventricle is high. So the pressure in the ventricle is high when it is contracting and we have that cyst squeeze. So we are gonna say Sicily, at least typically it will be higher during Sicily. All right, that's our table. Again, just knowing the structures of the heart, how they relate to each other and understanding this relationship of pressure, you should be able to fill all this stuff out on your own without having to memorize it. Now again, we are gonna go through it in more detail, looking at the heart coming up or then you got more practice problems. Give them a try.
3
Problem
Problem
When the pressure inside the ventricle causes the atrioventricular valve to close and the semilunar valve to open, which statement about the heart is true?
A
The ventricles are in systole.
B
The ventricles are in diastole.
C
The pressure in the left ventricle is greater than in the aorta.
D
Both A & C are correct.
4
Problem
Problem
For the atrioventricular valves to be open, the pressure in the ventricles must be:
A
Greater than the pressure in the pulmonary artery.
B
Greater than the pressure in the aorta.
C
Greater to the pressure in the atria.
D
Less than the pressure in the atria.
5
concept
Events in the Cardiac Cycle
Video duration:
9m
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We previously looked at how pressure changes in the ventricles, whether they're in cysto or diastole, whether they're contracting or relaxing is really gonna dictate the movement of blood and the opening of closing of valves in the heart. Well, now we wanna take those ideas and apply them to the actual heart and look at how this works through one heartbeat, the events of one heartbeat, we call the cardiac cycle, the filling of blood into the heart and then the squeezing of the heart to push that blood into circulation. So as we start looking at the cardiac cycle, we're gonna say that there's actually four events that we wanna name and describe in this cardiac cycle. And we're gonna break these events up based on sort of two factors. First, whether the ventricles are in systole or diastole. Remember the ventricles, that's the main mass of the heart and they contract with a lot of pressure. So whether they are in systole, that cystically squeeze, contracting or whether they're in diastole, that diastole drops, the pressure drops during relaxation, whether they're squeezing or relaxing, that's gonna dictate these pressure changes more than anything else. So that's number one. And number two, we wanna look at whether blood is moving in the heart, the pressure changes we said are gonna open and close valves. Now, you may think isn't the blood always moving, but there's actually gonna be some periods when all the valves are closed, all the doors in the heart are shut. So the blood actually doesn't move for some short periods and that's gonna break up this cardiac cycle some as well. All right. So let's take a look. You can see we have this image here of the heart. We have blood on it. Now, this is gonna be actually a an animation. I'm gonna play through this so we can watch through the cardiac cycle. Now, if you're following along on your student pf you'll see that we have, you already have these uh uh phases of the cardiac cycle named and you have freeze fra from this animation there. Now, I like to show this animation because I think it's important to remember that this is a process. It doesn't jump from one to the other. These are changes that flow from one to the other. So to get that idea, let's watch one cardiac cycle first before we name things and just know here we're going in very slow motion. All right. So first up, we have the blood flowing into the ventricles, the ventricles fill up. Now, the ventricle squeeze that closes the A V valve, pushes open the semi lunar valve, the blood flows into the arteries. Now, the ventricles start relaxing, that semi lunar valve closes, then that a V valve opens again. So it can fill. That was one heartbeat, one cardiac cycle. All right. So let's go through what just happened. So, the first thing that happened, we're gonna call ventricular filling. All right, from that name, it's should be pretty obvious what's going on here. The blood flows through the atria and into the ventricles. Now, as we go through this, for each one of these stages, we're gonna try and name are the ventricles in systole or diastole is the ventricular pressure high or low and are the A V valves and the semi lunar valves open or closed. So for ventricular filling, if blood is flowing into the ventricles, well, that means that the ventricles must be in diastole. Remember, diastole means that they are relaxed. That means that there's very low pressure. So the ventricular pressure is going to be low. And we can see here on the image, I'll actually just advance it just a little bit here. We have that blood flowing into the heart. That means that the A V valves, those are open those valves between the atria and the ventricles because the pressure in the ventricle is lower than the pressure in the atrium, the semi lunar valves, you'll see those are closed because the pressure in those arteries is gonna also be greater. Well, this time it's gonna be greater than the pressure in the ventricles. All right. So we're gonna fill up and then those ventricles are gonna start contracting. So I'm gonna advance our video here. They start contracting those A V valves close and I'm gonna stop it right there. All right, here we've started contracting. The A V valves have been pushed closed because the pressure has risen. But you can see the semi lunar valves, those valves from the ventricles into the arteries, they haven't opened yet. So we're gonna call this stage isovolumetric contraction. And again, if we break down these words here, we can see what's happening. Iso, well, iso means the same and volumetric, it refers to the volume, the volume isn't changing, but the ventricle is contracting. So we're gonna say here the blood is contained in the ventricles as they contract. All right. So what's happening in these things? We wanna fill in? Well, the ventricles, they're contracting. So that means that they are in cyst, we have that cyst squeeze going on. That means that, well, if they're contracting, that means that the pressure in the ventricles. Well, I'm gonna say here it's rising, it's not as high as it's gonna get, but it is going up. We can see the pressure has risen enough that the pressure in the ventricle is now greater than the atria that has pushed that A V valve closed. But the pressure in the ventricle has not gotten enough to be greater than in the arteries. So that semi lunar valve is also closed. All right, all the valves, all the doors to the ventricle are shut. So it means even though it's contracting, the pressure hasn't changed enough to actually move the blood. So we're in an isovolumetric stage, the volume is staying the same. All right, pressure is gonna keep rising though and we'll follow this along. It's gonna rise enough. It's gonna push open that semi lunar valve and I'll pause it again right there. You can see now that blood is getting pushed out of the heart. So our next stage here and I'm actually just gonna remove myself from the video for a second so that I can fill this in. You can see now we're pushing blood out of the heart. We're gonna call that ventricular ejection. The blood is being pushed out of the, of the ventricle and we're gonna say the blood flows into the aorta and the pulmonary trunk. Well, in this case, the ventricles, if they're still contracting, that means that they are in systole, we got the systole squeeze going on and the ventricular pressure. Well, now it's enough to actually push blood out. So now it's higher than in the arteries. So we're gonna just say here the ventricular pressure is going to be high. All right. Now what's going on in our A V valves, those atrioventricular valves. Well, if the ventricular pressure is high, it's gonna be pressure higher than what's in the atria. So these are still gonna be closed, but now they've risen enough to push open those semi, semi lunar valves. So these valves are gonna be open. All right. Uh Come back on the screen here. Ok. So next, we've now pushed the blood out of the heart. Let's follow it along and see what our final stage is gonna be. So the blood gets pushed out of the heart and I'm gonna pause it right here. All right. Now, right now, you can see the ventricle has just started relaxing enough that you can see that semi lunar valve it's closed. So now our next stage, we're gonna call isovolumetric relaxation. So again, isovolumetric iso means the same volume refers to the volume. So the volume is not changing while the ventricles relax. So here the ventricles relax, no movement of blood in the heart. Well, if the ventricle is relaxing, that means that the ventricles have entered diastole. Well, if the ventricle is entered diastole, diastole drops, the pressure drops. So we're gonna say here the vent ventricular pressure is falling. It's not all the way low yet, but it is falling. It's fallen enough that those semi lunar valves have closed. That means the pressure in the arteries is now higher than the pressure in the ventricles. So semi lunar valves, I'm gonna say closed and it hasn't fallen enough for the A V valves to open yet. So the A V valves, those atrioventricular valves, those are also closed again. All the valves in the heart are closed, all the doors to the ventricles are closed. So, even though it's gone into diastole, that pressure is falling, it's dropping, the blood can't move. All right. Well, it's gonna fall enough and we are gonna have ventricular filling again, followed by ventricular filling. We'll get that isovolumetric contraction, followed by ventricular ejection, followed by isovolumic relaxation and ventricular filling over and over again. That's the cardiac cycle. It just keeps repeating and that's your heartbeat. All right. I'm actually just gonna pause it right there to uh close this out. We're just gonna say that we are gonna look at this one more time. We're gonna go through all this and try to put all the things that we've talked about that relate to a cardiac cycle, the heartbeat, the electrical conduction. We're gonna try and link all those things together. But before we get there, we have one more thing we wanna talk about and that's your heartbeat, your heart sounds, we wanna talk about listening to your heart. We'll do that coming up. I'll see you there.
6
example
Cardiac Cycle Example 2
Video duration:
3m
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In this example, it says that the steps of the cardiac cycle are described below, match each description below with the phase of the cardiac cycle it describes and we see 1234 descriptions for each of them. It tells us what's happening with both sets of vowels and it tells us whether the Atria and the ventricles are in cysto or diastole. And then we see our 1234 stages of the cardiac cycle here. And so we need to match those things together. I just know you could do it either way we could start at the bottom and think what's happening each one and find the description that matches. I'm gonna do it the other way around. I'm gonna start with the ABC D and match it down to the stage that that describes the other thing that I wanna note here though is just that it's giving us for the uh Sicle and diastole information on both the atria and the ventricles. But remember what really just matters here is what's happening with the ventricles. So this information of whether the atria are in C systole and diastole. I actually don't really care, it's not important. So I'm just gonna cross that part out because it's not relevant for the answer. All right. Well, so now a says both sets of valves are closed and the ventricles are in diastole. Well, knowing that which stage of the cardiac cycle do you think that represents? Well, both sets of valves are closed. That means that blood cannot move through the heart because all the valves are closed. That must means that it must be an isovolumetric stage. So we have two isovolumetric stages. But then it says that the ventricles are in diastole, diastole drop, the diastole drop, the ventricles are relaxing. So that has to be isovolumetric relaxation. So I'm gonna put an A here and I'll cross out that one and move down to B it says that the A V valves are open, the semi lunar valves are closed and the ventricles are in diastole. All right. Which stage do you think that represents? All right. Well, if the A V valves are open and the semi lunar valves are closed, remember we had that word Aven slough A V into the ventricle, semi lunar sl out of the ventricles. So the indoors are open. Well, that means that blood can flow into the ventricle because it is in diastole, the diastole drop, it's relaxing. So here the ventricle is filling with blood and that's the name of a stage right here. Ventricular filling. So, ventricular filling, I'm gonna put B on the line there. And in that one. All right. Next, we have c both sets of valves are closed. The ventricles are in systole. Which one do you think that one represents? Well, again, because both sets of valves are closed, that means that no blood is moving through the heart, which means it must be an isovolumetric stage. The ventricle is in systole, we get the cysto squeeze so it is contracting. So that means that I can put c next to isovolumetric contraction. And we've answered that one. Now, we only have one more option here, but let's just make sure it matches up. We have D the A V valves are closed, the semi lunar valves are open and the ventricles are in Sicily. All right. Well, if the A V valves are closed, the in valves are closed, the semi lunar valves are open the outdoors, the out valves are open and the vent ventricle, sorry, we have the systole squeeze. They're squeezing and pushing blood, pushing those semi lunar valves open. That happens during ventricular ejection, ventricular ejection, you're pushing the blood out of the heart. So that's gonna be option D that I've answered the question. We practice problems after this. See you later.
7
Problem
Problem
What event immediately follows the closure of the atrioventricular valves and coincides with the onset of ventricular systole?
A
Isovolumetric contraction.
B
Atrial systole.
C
Ventricular ejection.
D
Isovolumetric relaxation.
8
Problem
Problem
During which following phase (or phases) of the cardiac cycle is the blood volume in the ventricles constant?
A
Isovolumetric contraction.
B
Isovolumetric relaxation.
C
Ventricular ejection.
D
A & B are correct.
9
Problem
Problem
If the pressure in the ventricles is higher than in the atria, which of the following statements must be true?
I. The atrioventricular valves are closed.
II. The semilunar valves are open.
III. The ventricles are in systole.
A
I only.
B
I and II.
C
I and III.
D
II and III.
10
Problem
Problem
True or False: if false, choose the answer that best corrects the statement.
Ventricular filling is defined as the period that the atria are in systole.
A
True.
B
False; ventricular filling is defined as the period that the semilunar valves are open.
C
False; ventricular filling is defined as the period when the AV valves are open, and the SL valves are closed.
D
False; ventricular filling is defined as the period when the pressure in the ventricles is greater than in the atria.
11
concept
Sounds in the Cardiac Cycle
Video duration:
7m
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You're almost certainly very familiar with this sound, that sound of the heartbeat, very familiar dldld. It is the heart. Now, we wanna talk about what causes those sounds in some detail here and we're doing it now because it directly relates to the cardiac cycle and how pressure changes in the ventricle affect specifically the valves. So we're gonna start out by saying that the heartbeat sounds are created when valves close and that's important. Some people have a misconception that it's the blood going through the heart that you hear or it's the valves opening and closing that you hear really when you listen to a heartbeat, you're really listening to those valves closing. Now, to understand why that is, I really like that analogy of a door. These valves are very much the doors to the ventricle. Well, as I walk through a door, if I open the door, it doesn't make a lot of noise as I walk through it. Not much noise there as I slam it behind me, that makes a lot of noise. The same thing with these valves as blood pushes them open, that's pretty quiet as blood flows through them. That's typically quiet, but as the change in pressure causes these valves to slam shut that you can hear. All right. So that means there's gonna be two basic heart sounds because there's two times in the cardiac cycle when valves close. Now to remind us of this, we have these stages of a cardiac cycle uh written out here sort of in this circle. And for each one, we have an image of the heart to remind you what's going on during that stage. So the first heart sound, let's start talking about ventricular filling. Remember in ventricular filling, the pressure in the ventricle is gonna be lower than the pressure in the atria. That means that that atrioventricular valve that a V valve is open and blood is moving from the atria into the ventricle. Well, as we go from ventricular filling over to isovolumetric contraction over here. Well, that involves the ventricle starting to contract, they're gonna go into cysto that cyst squeeze. Now that is a really rapid and fast change in pressure where the pressure in the ventricle shoots up. So if the pressure in the ventricle shoots up, that's gonna cause that a V valve to slam shut. So that first heart sound, what we often call the lub and that lub dub we're gonna say here is the ATRIO ventricular atrioventricular valves that mitral valve and the tricuspid valve. It's when those valves close and the atrioventricular valves when, especially when compared to the semi lunar valves, they're kind of bigger heavier valves. And this pressure change that happens here from the time you're going in uh ventricular filling when the, um, when the ventricles in diastole and then it goes into systole, that's a really fast and dramatic change in pressure. So you wanna think about this, these are kind of big, heavy doors that you're slamming shut with a lot of force. So that means that this sound is gonna be louder and a little longer lasting than the heart than the second heart sound. All right, with that in mind, when we go from isovolumetric contraction to ventricular ejection here. Well, that does involve valves, but here the pressure in the ventricle is gonna raise enough that it's gonna push open those semi lunar valves. Well, remember as you push open a valve, you don't really hear anything as you get into ventricular ejection. That means that blood is flowing out of the heart through those semi lunar valves again, going through a door doesn't make a lot of sound. But then as you go from ventricular ejection and you go over to isovolumetric relaxation. Well, that's gonna involve the closing of those semi lunar valves. So that second sound, what we often call the dub and that love dub. This is going to be the semi lunar valves closing and these semi lunar valves close when the pressure in the ventricles drops down below the pressure in the arteries. Now, that change in pressure in the ventricles as it goes from systole into diastole. It's not as fast and as dramatic, it just sort of starts relaxing. And so it's not as big a pressure change or it's rapid a pressure change. And those valves again, they're kind of smaller. So that's why that dub is usually heard as sort of a softer, shorter sound than the first heart sound that love. All right. Just to finish out our cardiac cycle. Here we go from isovolumetric relaxation to ventricular filling to go from one to the other there. Well, now the pressure in the ventricle just falls enough that it falls below the pressure in the atrium. That means that that uh a V valve gets pushed open again, you can't really hear a valve open and then during ventricular filling, blood is flowing from the atrium into the ventricle, you can't really hear that again. So now I'm gonna play these heart sounds again. And as you listen to it, really, you think we are hearing the atrioventricular valve close, then the semi lunar valve, that's the lub followed by the dub. Love, love, love. All right. Of course, people don't listen to a heart though to hear a perfectly healthy heart. It's always nice when you do. But the reason your doctor takes out a stethoscope and listens is to see if there's something wrong. So let's talk about the basic things you can hear when you're listening to a heart. So the regularity and the timing of those heart sounds can really help indicate different heart valve pathologies. Now, just to be clear, a doctor is listening to more than just for the valves. But if we're listening the valves closing, that's the main sound. If there's a problem with those heart sounds, it usually indicates something that is wrong with the valves. Now, when there is something wrong, we usually call that a murmur and a murmur is just a sound created by a turbulent flow of blood. Now, typically again, we said that the blood going through, you can't really hear it because it's, you know, going through in the direction it's supposed to go no problems, but sometimes you'll hear something like a lab. The Bush, la de la de Bush. Well, that whoosh at the end might indicate something like those semi lunar valves aren't closing all the way you get a turbulent flow of blood as some flow, blood flows backwards through the semi lunar valves. Similarly, you might hear something like a labutta, labutta, labutta, that Bush after the love. Well, that would indicate something wrong with the A V valves. Now, it is important to note heart murmurs can be serious, but often they are harmless and it takes someone who is trained listening to the heart and even other tests, sometimes to know the difference we call a harmless heart murmur, an innocent murmur and it can be caused by lots of things, even just becoming dehydrated, can temporarily cause your blood flow to be more turbulent and can cause a heart murmur. It's especially true though in Children, no Children can have very serious heart valve problems. I don't want to give you the idea that they can't. But because children's hearts are smaller, they're not as tough, they're not as robust. There tends to be just more vibration and turbulence going on. So oftentimes Children will have, uh, minor heart murmurs that we call innocent murmurs that eventually they grow out of. All right, those are the heart sounds. We're gonna one more time go through all of this cardiac cycle trying to tie together everything that we've learned about it. We'll do that coming up. It's gonna be fun. I'll see you there.
12
example
Cardiac Cycle Example 3
Video duration:
3m
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Here, it says that heart sounds are made at the transition from one stage of the cardiac cycle to the next, we wanna identify which heart sound would be heard at the start of each phase of the cardiac cycle. And if there is no distinct heart sound at the beginning of the phase, we can write none. All right. So we have our four phases here. And for each phase, we see a diagram of the heart sort of reminding us what's going on there. So let's go through them one by one. Remember these phases start with either the opening or the closing of the valve. And so let's think which ones would be able to hear. So we'll start with ventricular filling. Do you think you could hear the start of ventricular filling in? Why? Well, ventricular filling is really sort of defined as these A V valves being open? When those A V valves are open, blood from the atria can flow through the A V valves and fill up the ventricles. The ventricles are in diastole in that time they are relaxed. Well, the opening of those A V valves is what starts ventricular filling can you hear the opening of a valve? No, you can't. So there's gonna be no heart sound or I'm gonna write none that you can hear at the start of ventricular filling. All right, that brings us to isovolumetric contraction. Will you be able to hear the start of that phase? And if so why? Well, isovolumetric contraction contraction, this means that the ventricle goes into cyst, that cysto squeeze the pressure shoots up and that pressure shooting up is what causes these A V valves to snap shut. When they snapshot, you can hear that. That's that first heart sound. We can write that first heart sound as S one or we can write it's the l of the heart if we're being a little less technical. All right now isovolumetric, remember it's snapped these A V valves shut, but the pressure hasn't risen enough to push these semi lunar valves open yet. So the blood can't go anywhere because all the doors, all the valves to the ventricles are closed. All right. That brings us to ventricular ejection. What starts that? And will you be able to hear it well, in ventricular ejection, your heart, your ventricle is still in systole and it is now squeezing enough, the pressure goes enough that it pushes open these semi lunar valves and blood is ejected or pushed out of the heart. So, could you hear that? No, you cannot hear the opening of a valve. So you can't hear that. So we're gonna write none. All right. That brings us to isovolumetric relaxation. Here you go. Relaxation behind my head there. All right. Isovolumetric relaxation. Can you hear that? And if so why? Well, relaxation, that means that the heart is going into diastole, the ventricles are relaxing. That's gonna lower pressure as that pressure lowers. Well, you're gonna have some back pressure uh from the arteries here and that's gonna snap the semi lunar valves, clothes, the snapping of those semi lunar valves clothes. That's gonna be heart sound. We're gonna call that our second heart sound or what we can sometimes just write as S two or if we want to be a little less technical about it, we can call it the dub in that love dub of the heart. All right. Remember isovolumetric. That's because now all four valves are closed, all four valves are closed but relaxation. It's still in diastole. But because the valves are closed, there's no change in volume in that ventricle. Ok. Again, remember the heart sounds are the valves closing and that's uh those valves opening and closing are the beginning and the ends of these phases. So those heart sounds should line up with the starts of both of those isovolumetric phases. All right, more practice problems to follow. You should give them a try.
13
Problem
Problem
Using a stethoscope, you listen to the heart of a patient in their early forties. You hear a clear 1st heart sound (lub), but the second heart sound is muffled and followed by a whooshing noise. What structure could be dysfunctional in this patient?
A
Mitral valve.
B
Right atrioventricular valve.
C
Aortic valve.
D
Both A & B could be the cause.
14
concept
Cardiac Cycle: Putting It All Together
Video duration:
13m
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We now want to spend some time trying to tie together all these different concepts that we've talked about that relate to the cardiac cycle. And we're gonna do it by making one big graph here. Now, I'm gonna fill in this graph step by step as we go. If you're following along in your student PDF, you'll see it's already filled in for you a graph like this. You are very likely to see either because your professor is gonna teach from it or almost certainly it's in your textbook, a graph like this is great because it shows all the different things we've talked about and how they relate to each other. But I also understand it can be kind of confusing and a little bit overwhelming the first time you see it. So that's why we're gonna try and put it together piece by piece. So I'm gonna start at the very top and we're gonna start with this electrocardiogram or the ECG. So we're gonna draw in our ECG here and you should be familiar with this shape. Now, we're drawing it on a slightly different scale here. So it might look a little bit more stretched out, but we can still see all the parts we're familiar with. We see here the P wave, the P wave. Remember that's that Atria depolarizing. We see that QR S complex, the QR S complex, that's the ventricles depolarizing. And also the atria rep polarizing. We see the T wave, remember the T wave is the ventricles rep polarizing. And then if we follow it all the way down, we see the P wave starting again for the next heart contraction. All right, remember those depolarizations. That's those contractile cells in the heart go, that's the action potentials in those contractile cells. And that's the stimulation for them to contract. So we can relate this ecg to our cysto and diastole of the heart. Remember, cysto squeeze, that's when the heart is contracting and diastole drops, the pressure drops when the heart relaxes. So we can do that for both the atria and the ventricles. So let's start by looking at the atria, we can draw this in and we can see that the systole occurs. Well, it starts at that P wave, that's when the atria depolarize and it ends basically at that QR S complex when the atria rep polarize and the rest of the time it's in diastole, the ventricles. Well, you can predict what's gonna happen there. The ventricles go into systole during that QR Ss complex when the ventricles depolarize and they go back into diastole around that T wave when the ventricles rep polarize. Now, before we go on, I'm just gonna put some sort of gray bars here on the end where we wanna look at one cardiac cycle. And so we have a little bit more than one cardiac cycle drawn here for one cardiac cycle. We just wanna focus on the white part and outside of that, that's sort of just drawn in so we can see the beginnings and ends leading in and out. Now, here, we're defining this cardiac cycle as starting with cysto of the atria or the P wave of that atria and ending when the atria goes into cysto again. Now, I just wanna note that's different than how we broke it up when we talked about the events of the cardiac cycle. Now we're gonna look at that and compare that later on here. But just remember this is a cycle. It's kind of like a circle. There is no strict, strict beginning and end. So it's all right if we start or end in a different place because really, hopefully your heart doesn't start and end beating. Hopefully, it just keeps on going from one heartbeat to the next. All right, the next graph we're gonna draw here, this is pressure and you can see here it goes from zero up to 120 millimeters of mercury. Now, when we draw this in, we're just gonna be looking at the left side of the heart, we're gonna be looking at the left atrium, the left ventricle and the aorta, if you wanna think what's happening in the right side of the heart, the shapes of the curves will basically be the same, but the values are gonna be different because it's a lower pressure system. Ok. So first remember it's the systole and the diastole of the ventricles that really drives this process. And that's when I drew in Sicily and diastole up there. I made that sort of a bolder color that's gonna be what's really driving things. So let's look at this left ventricle first. Well, we can follow it along. We say over there, there's a little bump and that happens when the atria uh goes into cyst, that's the blood being pushed into that ventricle. You get a little raise in pressure, but really the main thing that's happening here, right? When the ventricle goes into systole, you get this major change in pressure, the pressure stays really high basically, until it goes into diastole again and diastole, the pressure drops. All right, we can compare that to the pressure in the aorta. Now, remember the aorta is part of that systemic circulation. It's a high pressure system. So the pressure here is always going to be high. It starts out sort of level, going down a little bit and then it gets that push from the cysto of the ventricles that blood gets pushed into the aorta. And you can see the pressure rises, it basically follows that shape of the curve of the ventricle, um, until the ventricle goes back into diastole and then it sort of levels out. Again. You can see there is one sort of funny blip up there. We'll talk about that in a second. What makes that happen. But we can also compare that to the pressure change in the atrium. So you can see here the atrium it's low pressure the entire time. You can see one little blip when the uh atria go into systole. So that's it just sort of squeezing down, pushing the blood into the ventricle. You can see another little bump when the uh ventricles actually contract. That's just because the ventricles are so massive that it sort of distorts the atrium and there's gonna be a little bit of ray and pressure there because everything is just started going crazy in the heart at that point and then it just basically stays low the rest of the time. All right. Now, we said what's really important and what's driving the movement of blood and the opening and closing of valves is the relative pressure in these different places. So what's gonna be really important on a graph like this is looking for when these pressure plots cross and they're gonna cross in four places and when they cross, we're gonna be seeing valves open and close. So let's go through these one by one. We say here when the pressure plots cross Well, at number one, you see right here, well, here we see the ventricle was at a low pressure and then it goes into cystically. So we have this massive increase in pressure and the pressure increases in the ventricle and it crosses that pressure line of the atrium, it goes higher than the atrium. That means that, that a V valve, well, that gets pushed closed, the A V valve closes at that point. Well, now we can follow this along. We have that pressure in the ventricle, it's increasing, increasing. And then we see the next time it crosses a line is here at two here. Now, the pressure in the ventricle is greater than in the aorta. So now that pressure is pushing hard enough that it actually pushes blood into the aorta. That means that that semi lunar valve is going to open. All right, we keep following along and these two curves basically follow each other. The ventricular pressure is just a little bit higher until three. Here we see as the ventricle goes back into diastole, we can see that the pressure lines cross one more time. Well, now the pressure in the ventricle has fallen below the pressure in the aorta. That means that the blood in the aorta is gonna sort of start to flow backwards just a little bit until that semi lunar valve closes. So at three, we see that semi lunar valve close and that's why you get this sort of funny little blip in pressure here in the aorta goes up just a little bit and then it goes back down. It's that blood sort of starting to flow backwards. The valve closes, it sort of hits that closed valve causes a real quick spike in pressure before it sort of equalizes out again. Ok. We can follow this ventricular pressure some more. Well, now the ventricle is in diastole, the diastole drop, we see this pressure dropping until down here at four. It crosses that pressure plot of the atrium again. So now the pressure in the ventricle is lower than the pressure in the atrium. That means that the blood in the atrium can push through that a V valve that a atrial ventricular valve, the A V valve opens and blood can start filling up the ventricle again. All right, just a quick note on some of these pressures, you'll notice uh the pressure in the aorta might be familiar to you. We have the lowest pressure it gets is 80 the highest pressure it gets is 120. Well, if you ever had your blood pressure taken, you probably had values that were similar to 1 20/80. That's a normal healthy blood pressure. The 120 that's your systolic blood pressure. That's the pressure in the aorta when the ventricle is in systole, the 80. Well, that's the lowest the pressure gets. That's the pressure that happens in the aorta when the ventricle is in diastole. That's your diastolic blood pressure. All right. Now, we've tied those things together. Let's think about heart sounds. Right. Remember heart sounds are when the valves close and we have the valves opening and closing. I sort of think of them as doors opening and closing. You can hear a door slam shut much better than you can hear a door open. So we hear the heart sounds when those doors shut. So we can look at our heart sounds. There's two places when the door is shut, when these valves shut, they shut at one and three in our, in our plot there. So at one, that's when that A V valve gets slammed shut. And you can see how dramatically the pressure changes there. Right? The pressure in that ventricle is low, low, low and then all of a sudden bam it shoots way up. So that valve gets slammed shut and it's a pretty big and heavy valve. So if you slam a big and heavy door, you get a relatively loud sound. That's that lub of the heart. Now, at three, we can see the pressure change isn't quite as dramatic and the valve, well, a semi lunar valve is smaller and lighter than those A B valves. So when you shut a smaller, lighter door with less force, you get a slightly smaller sound and that's that dub that second heart sound. All right. Well, the next thing we wanna look at is how much blood is in the ventricles. So here we're gonna graph ventricular volume, how much blood is in there. And this goes from zero up to 150 mL. So we're gonna draw that in. And the basic thing that you wanna see is that when the blood or I'm sorry, when the ventricle is in cysto right here. Well, that volume is going down, it's pushing blood out of the heart when the heart is in diastole here and over at the beginning of the graph, well, blood is coming into the ventricle. That curve is rising, right. So we can relate that to our stages of the cardiac cycle, our events of the cardiac cycle. So remember we had four of them. The first one, we called ventricular filling and ventricular filling is whenever blood is flowing into that ventricle. And that's gonna happen whenever the pressure in the ventricle is lower than the pre pressure in the atrium. So we've highlighted all those portions here in blue and they're labeled A. So starting here going around and then also at the beginning of the cardiac cycle. All right. Well, then we had that isovolumetric contraction, isovolumetric, the volume doesn't change but the heart is contracting. So you see the ventricle goes into systole at B but between uh one and two there, all the valves are closed. So that's our section B, the pressure is rising, but the blood can't go anywhere because the pressure has not gotten high enough to push that semi lunar valve open and push the blood into the aorta isovolumetric, the same volume while the heart is contracting. All right, we follow this along. We next have ventricular ejection and ventricular ejection. We can see here is when the heart is pushing blood out of the heart, we see the volume falling and that is really most of the time that the heart is in Sicily. So the heart is cyst, it's pushed all the blood out. And then our final stage here is gonna be isovolumetric relaxation, isovolume, volumetric relaxation. You can see here, we have labeled it as d this is the time when the heart is in diastole, that pressure is dropping but all the valves are closed, it's dropped enough that that semi lunar valve closes, but it hasn't fallen enough that the A V valve opens again. All right, I know that was a lot and I know this is confusing but if you can tie all those things together, if you understand how that ECG relates to these changes in volume, you're doing pretty good. That just wanna say good job. Everybody see you in the next video.
Video duration:
3m
Play a video:
Our example says on the graph below identify the following areas. And we have four things that we need to look for on this graph before we look for in low, let's just orient ourselves to the graph here. This is that pressure graph that we looked at previously. On the y axis, we have pressure in millimeters of mercury and on the X axis, we have time, there's three lines on this graph here in black. We see this as the pressure changes in the aorta. The red line is the left ventricle and the purple line represents the pressure changes in the left atrium. All right. Now we've seen that let's see what it wants us to do. It says a circle the area or areas of the plot where the atrial ventricular valves will be open. All right. So take a look at the graph. When do you think those A V valves will be open? Well, remember the A V valves will be open whenever the pressure in the ventricle is lower than the pressure in the atrium that allows blood from the atrium to push that A V valve open and flow into the ventricle Now, on this graph, that means that the, it's gonna be the times when the red line is lower than the purple line. So I see that here and I see that here. Now you'll see that on the graph here, those areas have that sort of bluish background that represents that this is the period of the cardiac cycle that we call ventricular filling. All right. So I've done A, I'm gonna cross that out. Next. We have B put a box around the area or areas where the semi lunar valves will be open. All right. Again, take a look on this graph. Where do you think the semi lunar valves will be open? Well, the semi lunar valves are gonna be open whenever the pressure in the ventricle is greater than the pressure in the artery. That means that the blood is gonna be pushing out of the ventricle and will push that semi lunar valve open. So, in this graph, it's when this red line representing the pressure in the left ventricle is greater than the pressure in this black line representing the aorta. And that's this area right there. On this graph, it has that sort of beige background representing the stage of the cardiac cycle. We call it ventricular ejection when blood is being pushed out of the heart. All right, I'm done. B I'll cross that out next. It says c place a star where you would hear the first heart sound, the love of a heartbeat. All right. So where would you put that star? Well, the L right, that's the first heart sound. Remember the heart sounds come from the valves closing. And we said that whenever the lines cross on this graph that represents a valve, either opening or closing. So where would that first heart sound come? That's when the A V valve closes and that's when that pressure in the ventricle shoots up and crosses that line. That's the pressure in the atrium. So that happens right here. All right. Next, we have place an X where you would hear the second heart sound, the dub of a heartbeat. All right. So where would you put that? X? Well, I would put that X. Well, again where these lines cross and here where the valve is going to close is where the pressure in the ventricle falls down again, below the pressure in the artery or the pressure in the aorta that happens right here. So I will put my X right here on the graph and with that, we've marked up the graph how we were asked again, remember always think what is the relative pressure in these two different places? And that's gonna tell you what's happening in the heart. We'll practice it some more. I'll see you there.
16
Problem
Problem
During which phase or phases of the cardiac cycle does the ventricular pressure change the least?
A
Ventricular filling.
B
Isometric contraction.
C
Isometric relaxation.
D
Both B & C are correct.
17
Problem
Problem
During which phase of the cardiac cycle do you hear the second heart sound?
A
Ventricular filling.
B
Isometric contraction.
C
Isovolumetric relaxation.
D
Ventricular ejection.
18
Problem
Problem
You are listening to the heart through a stethoscope. When you hear the first heart sound, which of the following options correctly matches the structure to the pressure change that would be most responsible for producing that sound?