If you're seeing this message, it means we're having trouble loading external resources on our website.

如果你被网页过滤器挡住,请确保域名*.kastatic.org*.kasandbox.org 没有被阻止.



有没有考虑过心脏为什么有这种声音?心脏瓣膜一张一合,导致了最终我们听到的有规律的心跳节奏...里希(Dr. Rishi Desai)是一名儿科传染病医师,是可汗学院团队一员。 Rishi Desai 创建




if you take a good long listen to your heart you'll actually notice that it makes sounds and those sounds are usually described as lub-dub lub-dub lub-dub and if you actually try to figure out what that would spell out like usually it's something like l ub d ub and it just repeats over and over and over and sort of figure out where those sounds come from what I did is I took that diagram of the heart that we've been using and actually exaggerated the valves made them really really clear to see in this picture and we'll use those valves to kind of talk through where those sounds are coming from so let's start by labeling our heart so we've got at the top blood is coming into the right atrium and going to the right ventricle it goes off to the lungs comes back into the left atrium and then the left ventricle so these are the the chambers of our heart now keep your eye on the valves and we'll actually talk about them as the blood moves through so let's start with blood going from the right atrium this way into the right ventricle now at the same moment that Bloods actually going from the right atrium to the right ventricle blood is actually also going from the left atrium to the left ventricle and you might think well how is that possible how can blood be in two places at one time but now remember that blood is constantly moving through the heart so in a previous cycle you had surely had some blood that was coming back from the lungs and that's what's dumping into the left ventricle and in a new cycle you have a bit of blood that's going from the right atrium to the right ventricle so you have simultaneously two chambers that are full of blood the right and left ventricle now to get the blood into those ventricles the valves had to open and specifically let's label all the valves now so here you have here this is our tricuspid valve tricuspid and I'm going to label that as just a tee and then you have up here you have the pulmonary valve pulmonary valves and this will be just a pea and on the other side you've got the mitral valve which separates the left atrium from the left ventricle you've got the aortic valve they or take valve so these are the four valves of the heart and as the blood is now in the ventricles you can see that the tricuspid and the mitral valve are open so far so good now I've actually drawn the pulmonary valve as being open but it's not really the case and the answer is no because what happens is that as blood is moving down from the right atrium to the right ventricle let's say that I'm going to draw it in black black arrows represent the bad or the wrong direction of flow so let's say some blood is actually trying to go that way which is not the way it should be going what happens is that these two valves they based on their shape or actually knock they're gonna jam up they're gonna basically just jam up like this and they're not gonna let the blood pass through so this is what happens is that valve closes down and the same thing happens on this side let's imagine you have some backwards flow of blood by accident meaning that it's going in the wrong direction well then these valves are gonna close down so the white arrows represent the correct flow of blood and the black arrows represent the incorrect flow of blood so these valves shut down like that so now you can see how the valves the aortic and pulmonary valve are actually closed when the mitral and tricuspid valve are open so what happens after this and now our ventricles are full of blood right they're full of blood and let's say they squeeze they squeeze down and they jettison all the blood into those arteries well now you're gonna have this is actually going to close down let's say this arrow flips around these arrows become white because the direction of flow is going to be in the direction we want it it's gonna go this way and this way and to allow that of course I need to show you that these open up these open up and they allow the blood to go the way that we want it to go so now blood is going to flow through those two valves but similar to before you could have some backflow here right you can have backflow here and you can have backflow here so you can imagine now let's say you have a little bit of backflow that wants to go this way which is the wrong direction right well then these valves are gonna close up they're gonna say nope can't go that way they're gonna close right up and they're gonna not allow blood to go that way so this is gonna happen on both sides both ventricles and the valves shut and so basically the backflow of blood is not allowed because the valves keep shutting and when the valve snaps shut so for example right now the tricuspid valve and the mitral valve snapped shut well that makes a noise so when T and M snap shut that makes a noise that we call lub that's that first noise that first heart sound in fact sometimes people don't even call it lub dub they say well it's the first heart sound first heart sound and to make that even shorter sometimes people call that s1 so if you hear s-1 you know they're talking about that same exact thing and this dub is called the second heart sound second heart sound and no surprise just as before if that's s1 this is s2 so you'll hear s1 when the tricuspid and mitral valve snaps shut so far so good but you also know that if that's what's making noise you can kind of guess and it was a very smart guess that at the same time the pulmonic valve and the aortic valve just opened just opened so if the other valves snap shut these just opened right you can kind of assume that although the noise you're hearing is actually from here so what's happening with dub well the opposite and what I mean by that is let me now show you what happens a moment later well after after the ventricles are done squeezing after they're done squeezing then we get to a point where you might have a little bit of flow that way in that way just as I drew before and these valves snap shut as well so now these snap shut and as these snap shut because they don't want to allow backflow right they're gonna snap shut like that they make noise and so when you have dub you actually have noise coming from the pulmonic an aortic valve snapping shut snap shut and that must mean that then the other two valves just opened up the tricuspid and mitral just open you can assume that right and I didn't draw that in the picture let me update my picture now to show that so now these two have opened up these two are opened up and blood is coming in to the ventricles again so it's actually a nice little rhythm that you get going and every time these valves go open and shut listy you hear noise so you can kind of figure out what's happening based on and these actually oh let me erase that and then you have white arrows going this way and we've returned to where we started from so you basically have a full cycle and between these two so let's say from lub to dub so there's a little bit of space there like if you were to follow it over time over time this is what it might look like if this is a little time line you might hear love here or the first heart sound I'll just call it s1 and you might hear s2 here the second heart sound and then you'll hear s1 again over here and s2 and what's happening between the two so between these two this time lag here is that blood is actually squeezing out because the pulmonary and aortic valves just opened is squeezing out and going out to the hole so this is when blood is going to the body and sometimes we call that systole systole and between dub and the next lub so in this area right here well at that point blood is kind of refilling from the atrium into the ventricles and we call that diastole diastole so now you can actually listen to your heart and you can actually figure out well if you're listening to the sound between love and dub or the space and time between love and dub that's when you're having systole and if you're listening to or waiting for the sound to start up again so you just heard dub and you're waiting for love again then that that space and time is diastole