How does lung volume change? | Respiratory system physiology | NCLEX-RN | Khan Academy
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How does lung volume change? | Respiratory system physiology | NCLEX-RN | Khan Academy


So we talked about
inhaling and exhaling. And I’d mentioned that the key
first step for both of them is this change in volume,
going up in volume or going down in volume. But I didn’t really talk about
how that happens exactly, so I thought I would
jump into that now. And let me begin by telling
you that in the middle of your chest, you have this
enormous kind of bone that goes down. And I’m drawing it
out of proportion just to make it very clear
where this bone is. But you can go ahead and
feel on your own body this bone, which we call
either the breastbone, or the more technical
name is the sternum. So I’ll write that down here. The sternum is this middle bone,
and all the ribs on both sides attach there. So you’ve got a total of 12
ribs and seven pairs of them. Actually, I should
say 12 pairs of ribs. I don’t want you to
think there are 12 total. We actually have 24 total
and seven pairs of the ribs. So 14 ribs actually attach
directly to this sternum bone. So in white, these are the ribs. And between the ribs,
you actually have muscle. So I’m going to draw in 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 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 are going to
start moving outwards when your brain says, hey, I
want to take a deep breath. So these muscles are
going to contract. The ribs, I should say,
are going to move outwards. So these go out. And you also have–
let me just make a little bit of space on
this canvas– another muscle that kind of rides
down here and has kind of 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 diaphragm muscle. So we’ve got our
diaphragm muscle. And this one when it contracts,
instead of going out, it’s going to go down. So it’s going to
kind of flatten out. And I can actually draw this. If you can now just stick
with me for a moment, I’m going to erase
this dome-like shape. And I’m going to draw what it
looks like as it contracts. So when it contracts, it’s
actually going to be more flat. And this flat diaphragm,
as you can see, is now further down
than it used to be. And as it goes down, all
of the structures that are inside this space–
so the two lungs. And of course, I didn’t
draw the heart here. But the heart would be kind
of in this cardiac notch. If you want, maybe I could
even draw that heart here. They’re all going to kind
of physically move down. So this is our
heart and our lungs. They’re physically going
to be kind of drawn downwards and out. They are going to also move out
as the intercostal muscles move out. So you have expansion
of these lungs. That’s basically the idea. And if you were to kind of
zoom in on this to kind of see exactly what this
expansion looks like, when I say you have
more volume in the lungs, really what I should be saying,
if I wanted to be more exact, is that all the alveoli–
if these are the alveoli, let’s say this is
another branch. And this is another
alveoli right here. All these alveoli, they
are actually expanding. And you have about
500 million alveoli. If you can just kind of fathom
how big a number that is. It’s an enormous
number of alveoli. And if I was actually
drawing them, I would be here drawing forever. It would take
forever to write out this many different alveoli. But basically what happens
is that when the ribs go out and the diaphragm moves down,
these alveoli are actually being pulled out. They’re actually
being pulled outwards, so they are actually going
to 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 were
to take an even closer look, you’d 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. And elastin is basically
kind of like a rubber band, so you can kind of think of
elastin as a rubber band. And when the muscles
move down and out and the alveoli
are pulled open– let me actually now scroll up,
because you can kind of go back to the idea of inhaling–
what is happening, then? Well, you have a couple
things happening. One, you have muscles– I’ll
just write muscles contracting. 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
are stretched open. So those rubber bands,
those elastin proteins, are literally physically
being stretched opened. And keep that in mind, because
what’s going to happen then is when the muscles
relax, which is what happens when you
exhale, what do you think is going to
happen to that elastin? Well, if it’s like
a rubber band, if that’s what I’m saying
it’s going to be like, then the alveoli
are going to 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. You’ll see it really clearly. If you’re physically kind of
using your muscles to help pull this stuff
open, then the moment that you stop pulling
open, the moment that you stop contracting
those muscles now that you have a nice big
volume, what’s going to happen? Well, all these
elastin molecules are going to snap back. Let me do it with
a different color. Let’s do this color. They’re going to
snap back like this. All that protein
is going to want to snap back into
the original size. And when they do, this
thing gets smaller. So my alveoli goes back
to its original size, which was much
smaller than this. Let me actually just quickly
show that and show you that even though contraction
is what opened up things, it’s the recoil
that brings things back down to their normal size. And let me erase this to make
it kind of a 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. 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 going to use. And to exhale, when
you reduce the volume, it’s going to be driven
by this elastic recoil. So that’s a type of
elastic potential energy. So this process 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 then 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, and we’ll
pick up in the next video.

About James Carlton

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26 thoughts on “How does lung volume change? | Respiratory system physiology | NCLEX-RN | Khan Academy

  1. Thank you for sharing this! Your videos are really very helpful. From chemistry, biology, etc., your videos helped me enter med school. And now, your making things simpler for me.

  2. Great teacher. I have COPD and no one so far has shown me the mechanics of breathing so I can make sense of it.

  3. On behalf of the Respiratory Therapy Students a BIG THANKYOU on posting such helpful material…..THANKYOU!!! Extremely gratefull <3

  4. once again, ur lectures prove to be nothing but flawless and very easy to follow. Thank you so much. I actually am understanding the concepts now instead of memorizing them. Liked and subscribed, needless to say.

  5. I want to thank you once again for breaking everything down. I understand and have solidified the information you have given me. I will be taking my test tomorrow (Monday 4/13/2015) on both the respiratory and cardiac system. I believe that I will get an A for watching your videos in correlation with reading the PowerPoints and book. I really appreciate you creating this and other videos to help the general mass. I am very grateful!!! Thank YOU!!!!!

  6. nothing about the intrapleural fluid and the parietal , visceral pleura, incomplete information and very basic,

  7. You do an outstanding job covering information that tends to be very difficult for even the brightest students to learn. I can't thank you enough!

  8. sir heart is not present under the xiphous process of sternum where u have made, it is present under the 3rd and 4th ribs

  9. I've looked through quiet a few videos on YouTube tonight trying to get a better understanding of the lungs and how breathing works. Currently I am a student at Charter College for Medical Assistant. I've had a hard time understanding some of the reading material provided, because although there is some illustrations, I feel like there isn't enough visuals to go with what is being read. This video COMPLETELY covered everything I was hoping to find! It was very straight forward and easy to understand. Thanks!

  10. Dr. Desai, you are going to be the reason I have an RRT license in a year and a half. I appreciate all of the work you put into these videos.

    Thank you so much.

  11. Guys please help me first he says there are 12 pairs of them so 24 in total but then he says they’re 7 pairs or 14 I don’t get it please help.😔

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