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

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Stored elastic energy in large and middle sized arteries

See how arteries behave like sling shots, shooting blood (not rocks) onwards! Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.

Want to join the conversation?

  • orange juice squid orange style avatar for user seenachitresh07
    In this topic "stored elastic energy in large and middle sized arteries, i have a doubt that how the volume of artery increase with pressure because pressure is inversely proportional to volume,if my question sounds funny,please excuse.thank u
    (5 votes)
    Default Khan Academy avatar avatar for user
    • leaf green style avatar for user Joanne
      Your question is great. You have looked at it as though you are considering a piston in a canister. The canister or bottle does not have elastic fibers and muscle. Instead, in your body you have an intermittent pump,the heart, attached to pipes that expand like balloons. The heart contracts, a bolus of blood leaves it and moves to the aorta which expands to accept this larger volume of blood. The heart relaxes to fill again
      with the blood and now the stored elastic fiber energy in the aorta pushes that first volume of blood on down the artery. ( You feel a pulse in your wrist due to the contraction of the heart.) If you took a balloon and pumped air in it, it would expand and store the energy. Take the pump off and the air would squirt out of the balloon. That is like your aorta with its elastic fibers, pushing the blood. Furthermore the muscle can dilate and constrict changing the size of the pipes. Awesome stuff.
      (8 votes)
  • piceratops seedling style avatar for user seosol21
    So my understanding or my summary is, there are great pressure energy in systole which creates movement energy and elastic energy. And bood vessel will store this elastic energy and use in diastole phase where has little pressure energy. This elastic energy in diasotel will be converted into movement energy..right??
    (5 votes)
    Default Khan Academy avatar avatar for user
  • piceratops tree style avatar for user Sid Krishnan
    At , when he was talking about the elasticity of the artery during systole, was the drawing proportional to the actual change in size of the aorta? If not, does anybody know what the actual change is during systole?
    (3 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user NadeemAG98
    How to calculate the elastic potential energy stored in a given artery stretch during a pulsation ?
    (3 votes)
    Default Khan Academy avatar avatar for user

Video transcript

So let's say you're looking at the heart during systole. I'm going to write systole here. And the heart, of course, is going to pump blood out, and it's going to go into the aorta. So this is the aorta, and I'm not drawing it very accurately because we know that the aorta is not long and stretched out like that. It's got a lot of branches and definitely doesn't go off to the left like that. But just humor me for a second because I want to show you something really cool. Now, as the blood goes out into the aorta in systole, we know that the shape of the aorta does not stay like that at all, right? I mean, it's actually going to balloon out. And I'm actually going to even show you the old shape with a dashed line, just so you remember it. And then I'll show you the new shape just so that we can stay kind of consistent with the changes that I'm talking about. The new shape is going to look like this. It's going to be like a big balloon. And we know that this happens because we talked about the idea of compliance. You recall we talked about how if you have a certain amount of pressure and you actually want to look at the volume over pressure, that for an artery, like the aorta is an artery, you actually have changes like this. So basically as the pressure goes up, the volume goes up. And so we know that the arteries, specifically the aorta, is going to balloon out a little bit like that. Now here's what I want to show you and here's what I want to ask you, really, is to think for a moment about energy, OK? So think about energy and think about where the energy is. We know the heart is putting a lot of energy into each pump, right? We know this. So where is it going, exactly? Well, obviously a lot of it is going into movement, so there's a lot of movement energy. And we also know that there is a certain pressure energy. So if I was to actually just check the pressure in here, if I was to check the pressure, I know that there would be some pressure at that spot. So there's definitely pressure energy and movement energy. But see if you can think about where the third type of energy is. And I'll give you a clue, that there's blood actually rushing into this space, right? The reason that it's ballooning out like it is is because blood is pushing it out. And so if blood is pushing it out it's a little bit like a balloon. And a balloon has an elastic energy, and so do the aorta and other arteries. They have an elastic energy. So think about the walls of this balloon, if you want to think it is a balloon, as having elastic energy . Now, when I say elastic energy, one thing you might think of to help you kind of make this more concrete is this. Think about something you may have played with as a kid. I certainly used to play with these things, and I would chase-- actually scare parrots that were chewing on my peanuts away from the peanut tree by flicking stones at them. So I would load up on a slingshot with lots of elastic energy, and they wouldn't know what I was doing, obviously. But they would soon figure it out, because what I would do is I would aim my slingshot, and I would let go. I would let this snap back. And when it snaps back, you lose all that elastic energy, but your little rock is way over here. It's actually flown over here, and that's a great example of movement energy. So really what you're doing when you let go, in that one second that you let go of a slingshot, is you're converting all that elastic energy that you built up by pulling back into movement energy. And the same thing is happening here. So in diastole, you have a very similar situation. You have, again, your heart. And your heart is now refilling or getting a chance to kind of relax for just a moment. And that aorta begins to kind of collapse back down to its original shape. It doesn't actually take the exact original shape. And that's because there is some pressure still here, pushing it out. There is still some pressure. But we know that in diastole the pressure is lower, so of course, the volume is going to be lower. It's going to be more like it's-- it's going to be more collapsed, you could say. But this balloon has really done the same thing as my slingshot. The elastic energy of the walls has pushed back right here, pushed back all of this blood on both sides. And all the blood is moving up here as movement energy. So you have here movement energy again, same as before. But this time it's coming from conversion of this elastic energy, just like the slingshot. So your elastic energy gets converted to movement energy. And of course, there is still a little bit of potential energy as well. So you still have your potential-- pressure energy. Sorry, I said potential, I meant pressure energy. So you still have three energy sources but the big key is that you've really converted a lot of this elastic energy into movement energy when you go from systole over to diastole. So that's the beauty of your aortic and arterial walls.