Lub Dub Ever wonder why the heart sounds the way that it does? Opening and closing of heart valves makes the heart rhythm come alive with its lub dub beats... Rishi is a pediatric infectious disease physician and works at Khan Academy.
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- If you gave a good long listen to your heart, you might notice that it makes sounds.
- Those sounds are usually described as lubdub, lubdub, lubdub.
- If you ever tried to figure out what that would spell out like, usually it's something like lubdub.
- This repeats over and over and over.
- To figure out where those sounds come from, what I did was, I took the diagram of the heart that we'v been using
- and exaggerated the valves, made them really clear to see in this picture.
- We'll use those valves to talk through where those sounds are coming from.
- Let's start by labeling our heart, at the top blood is coming into the right atrium,
- going to the right ventricle, it goes of to the lungs,
- comes back into the left atrium and then the left ventricle.
- These are the chambers of our heart.
- Keep your eye on the valves and we'll talk about them as the blood moves through.
- Let's start with blood coming from the right atrium, this way into the right ventricle.
- At the same moment blood is going from the right atrium to the right ventricle,
- blood is actually also going from the left atrium to the left ventricle.
- You might think 'How's that possible? How can blood be in two places at one time?'
- Remember that blood is constantly moving through the heart,
- so from a previous cycle you've got blood that's coming back from the lungs
- and that's what's dumping into the left ventricle.
- In the new cycle you have a bit of blood that's going from the right atrium to the right ventricle.
- You have simultaneously two chambers that are full of blood, the right and left ventricle.
- To get the blood into the ventricles, the valves had to open.
- Let's label all the valves. Here you have our tricuspid valve.
- Up here you have the pulmonary valve.
- On the other side you have the mitral valve, which separates the left atrium from the left ventricle.
- Here you've got the aortic valve.
- These are the four valves of the heart.
- As the blood is now in the ventricles, you can see that the tricuspid and the mitral valve are open.
- I've drawn the pulmonary valve as being open, but is that really the case?
- The answer is no, because what happens is that as blood is moving down from the atrium to the right ventricle,
- let's say that, and I'm gonna draw it in black, black arrows represent the wrong direction of flow,
- let's say some blood is trying to go that way, which is not the way it should be going,
- what happens is, these two valves, based on their shape, they're gonna jam up like this.
- They're not gonna let blood pass through.
- This is what happens, that valve closes down.
- The same thing happens on this side. Imagine you have some blood flowing back by accident.
- Then these valves are going to close down.
- The white arrows represent the correct flow of the blood and the black arrows the incorrect flow of the blood.
- These valves shut down like that.
- You can see how the pulmonary and aortic valve are closed when the tricuspid and mitral valve are open.
- What happens after this?
- The ventricles are full of blood and let's say they squeeze.
- They squeeze down and they jam all the blood into the arteries.
- This is going to close down. This arrow flips around.
- These arrows become white because the flow is gonna be in the direction we want it.
- It's gonna go this way and this way.
- And to allow that, I'll have to show you, these open up.
- They allow the blood to go the way we want it to go.
- Now, blood is gonna flow through those two valves.
- Similar to before, you could have some back flow here, right?
- You can have back flow here and you can have back flow here.
- You can imagine, let's say you have a little back flow that wants to go this way, which is the wrong direction,
- then these valves are gonna close up.
- They'll say 'No, you can't go that way.' They're gonna close up.
- They won't allow blood to go that way.
- This happens on both sides and the valves shut.
- The back flow of blood is not allowed because the valves keep shutting.
- When the valves snap shut, for example the tricuspid and the mitral valve snap shut,
- well, that makes a noise.
- When T and M snap shut, that will make a noise that we call lub.
- That's that first noise, that first heart sound.
- In fact sometimes people don't even call it lubdub, they say, well, it's the first heart sound.
- To make that even shorter, sometimes people call that S1.
- If you hear S1, you know they're talking about that same exact thing.
- This dub is called the second heart sound.
- No surprise, just as before, if that's S1, this is S2.
- You'll hear S1 when the tricuspid and the mitral valve shut. So far so good.
- But you also know that if that is what's making the noise,
- you can guess that at the same time the pulmonic and the aortic valve just opened.
- If the other valves snap shut, these just opened.
- You can kind of assume that, although the noise you're hearing is actually from here.
- What's happening with dub? Well, the opposite.
- What I mean by that is, let me show you what happens a moment later.
- After the ventricles are done squeezing, then we come to a moment when you might have a little bit of flow that way and that way.
- Just as I drew before and these valves snap shut as well.
- So now these snap shut.
- As these snap shut because they don't want to allow back flow, they make noise.
- So when you hear dub, you have noise coming from the pulmonic and the aortic valve snapping shut.
- That must mean that the other two valves just opened up.
- The tricuspid and mitral valve just opened. You can assume that, right?
- I didn't draw that in the picture, let me update my picture now to show that.
- These two have opened up and blood is coming into the ventricles.
- It's actually a nice little rhythm that you get going.
- Every time these valves go open and shut, you hear noise.
- You can figure out what's happening.
- We've returned to where we've started from.
- You basically have a full cycle and between these two, let's say from lub to dub,
- there's a little bit of space there, if you were to follow it over time.
- Over time this is what it might look like if this is a little timeline.
- You might hear lub here, our first heart sound, let's call it S1 here, S2 here, the second heart sound.
- You'll hear S1 again here and S2.
- What's happening between the two, this timeline here, is that blood is actually squeezing out
- because the aortic and pulmonic valves just opened, blood is squeezing out and going to the whole body.
- This is when blood is going to the body. Or as we call it 'Systole'.
- Between dub and the next lub, so in this area, at that point blood is refilling from the atria to the ventricles
- and we call that diastole.
- Now you can listen to your heart and figure out, well if you listen to the sound between lub and dub,
- the space in time between lub and dub, that's when you're having systole.
- When you're waiting for the sound to start up again, that space in time is diastole.
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