How does lung volume change? Learn about how muscle contraction and lung recoil actually help the lungs change their volume with every breath! Rishi is a pediatric infectious disease physician and works at Khan Academy.
How does lung volume change?
- So we talked about inhaling and exhaling.
- And I mentioned that the key first step for both of them is kind of
- the change in volume: going up in volume and going down in volume.
- But I didn't really talk about how that happens exactly.
- So, I'll kind of jump into that now.
- And let me begin by telling you that in the middle of your chess,
- you have this enormous kind of bone that goes down.
- I'm drawing it out of proportion just to make it very clear
- where the bone is being.
- Go ahead and feel on your own body this bone which we called
- either the breast bone or the more technical name is sternum.
- Write that down here.
- The sternum is this middle bone and
- all the ribs on both sides attached there.
- So, you've got a total of 14 ribs and 7 pairs of them.
- Actually, I should say 14 pairs of ribs.
- I don't want you to think there're 14 in total.
- There are actually 14 in total and 7 pairs of the ribs.
- So 14 ribs actually attached directly to this bone, the sternum bone.
- So in white, these are the ribs.
- And between the ribs, you actually have muscles.
- So I'm gonna draw some of these muscles between the ribs.
- And these muscles are all going to have their own nerve
- that allows them to contract.
- So, these muscles are controlled by your body or your brain.
- And their name, let me just jot down here on the side, is "intercostal muscle".
- And "inter" just means "between". So, this is the name of the muscle.
- And "costal" refers to the ribs.
- So, when you see that word "costal",
- you'll know we're talking about the ribs.
- So what's between the ribs is these muscles: intercostal muscles.
- And they're gonna start moving outwards
- when your brain says, "hey I want to take a deep breath!"
- So, these muscles are going to contract
- and the ribs are gonna move outwards.
- So these go out. And you also have...
- Let me just make a little bit of space on this xxx.
- You also have another muscle that kind of right down here.
- And it has kind of a an upside down U shape to it.
- So I'm drawing it kind of like a dome. You can think of it as a dome.
- And this dome is the floor. If you remember,
- we talked about the floor of the thorax.
- So this is of course, our diaphram muscle.
- So, you've got a diaphragm muscle.
- And this one when it contracts, it's gonna go...
- instead of going out, it's gonna go down.
- So it's gonna kind of flatten out.
- And I can actually draw this if you just stick with me for a moment.
- I'm gonna erase this dome-like shape.
- And I'm gonna draw it when it looks like as it's contract.
- So when it contracts, this is actually going to be more flat.
- And this flat diaphragm, as you can see, is now
- further down that it used to be.
- And as it goes down, all of the structures
- that are inside the space, so the two lungs,
- and of course, I didn't draw the heart here,
- but the heart would be this kind of this cardiac notch.
- If you want me to, I can even draw that heart here.
- This is our heart here.
- They're all going to kind of physically moved down.
- So this is our heart and our lungs.
- They are physically gonna be kind of drawn downwards and out.
- They're gonna also move out as the intercostal muscles move out.
- So you have expansion of these lungs, that's basically the idea.
- And if you kind of zoom in on this,
- to kind of see exactly what this expansion looks like,
- when I say, you know, you have more volume, the lungs,
- really what I should be saying, if I want to be more exact,
- is that all the alveoli, if these are the alveoli,
- let's say this is another branch,
- this is another alveolar right here;
- all these alveoli, they are actually expanding.
- And you have about 500 million alveoli.
- You can just kind of fathom how big a number that it is.
- It's an enormous number of alveoli.
- If I was actually drawing them here... drawing forever, right?
- It'll take forever to kind of write out this many different alveoli.
- But basically what happens is that, when the ribs go out,
- the diaphragm moves down.
- These alveoli are actually being pulled out. They are actually pulled outwards.
- So they are actually gonna be getting larger in size.
- They literally look like they've grown in size.
- And, this is what they look like.
- And actually, if you take even a closer look,
- you'll see that these alveoli have around them, a bunch of protein.
- The cells around them have a bunch of protein.
- And this protein is called "elastin".
- And you can guess what elastin might do.
- It has kind of a similar sound to the word "elastic".
- Elastin is basically kind of like a rubber band.
- So you kind of thinking of elastin as a rubber band.
- And, when the muscles move down and out,
- and the alveoli pulled open,
- let me actually kind of scroll up,
- because you can kind of go back to the idea of inhaling.
- What is happening? Well, we have a couple things happening.
- One, you have muscles contracting. Muscles contract.
- And when I say "muscles", you know I'm talking about
- all those intercostal muscles in your diaphragm.
- And as a result of the muscles contracting,
- you have now the alveoli, alveoli are streched open.
- So those rubber bands are elastin, protein,
- are literally physically being stretched open.
- So the alveoli are stretched open.
- And keep that in mind, because what's gonna happen then is,
- when the muscles relax, which is what happens when you exhale,
- when the muscles relax,
- what do you think is going to happen to that elastin?
- Well, it's like a rubber band,
- if that's what I'm saying, it's gonna be like,
- then the alveoli are going to recoil. They are gonna recoil.
- And that's actually the driving force for why the volume goes back down.
- So if you have a bunch of rubber bands that you're stretching out...
- Let me actually bring up the picture so you'll see really clearly.
- If you're physically kind of using your muscles to help pull this stuff open,
- then the moment that you start pulling open, the moment that you,
- you know, stop contracting those muscles,
- now you have a nice big volume.
- What's gonna happen?
- All these elastin molecules are gonna snap back.
- We'll do it with a different color.
- I'll do it with this color.
- They are gonna snap back like this.
- All that protein are gonna snap back into kind of the original size.
- And when they do, this thing gets smaller.
- So my alveoli kind of goes back to its original size,
- which is much smaller than this.
- Let me actually show you that
- even though contraction is what opens up things
- it's the recoil that kind of brings things back down to their normal size.
- Let me erase this to make it kind of neater drawing.
- So you can see it now, inhaling, the way that we actually increase the volume,
- is by pulling things open through contraction.
- And this actually requires energy, right?
- Remember, you can't contract a muscle without spending chemical energy.
- So this takes chemical energy.
- And we usually think of this molecule ATP
- as the specific type of chemical energy we're gonna use.
- And to exhale, when you reduce the volume,
- it's gonna be driven by this elastic recoil.
- So that's a type of elastic potential energy.
- So, this process of kind of inhaling and exhaling
- is really a little different from each other.
- On the one hand, you're using ATP;
- you're actually burning through these molecules.
- And when you exhale,
- you're actually not using chemical energy anymore.
- You're just using that elastic potential energy,
- kind of the same sort of energy that you can imagine
- you would have if you snap a rubber band.
- So, let's stop there. We'll pick up the next video.
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