The lungs and pulmonary system | Health & Medicine | Khan Academy


I’ve done a bunch of videos
already on respiration. I think even before those
videos, you had a sense that we need oxygen and that
we release CO2. And if you watched the videos on
respiration, you know that we need the oxygen in order to
metabolize our food, in order to turn our food into ATPs
that can then drive other types of cellular functions–
or anything that we have to do; move, or breathe, or think,
or everything that we have to do. And that through the process of
respiration, we break down those sugars and we release
carbon dioxide. So in this video, what I want to
do is take a big step back and think about how we actually
get our oxygen into our body and how we release it
back out into the atmosphere. Another way to think about it is
how we ventilate ourselves. How do we get the oxygen in, and
how do we get the carbon dioxide out? And I think any of us could at
least start off this video. It starts off in either
our nose or our mouth. I always have a clogged sinus
so I often have to deal with my mouth. I sleep with my mouth often. But it always starts in our
nose or our mouths. Let me draw someone with
a nose and a mouth. So let’s say that this
is my person. Maybe his mouth will be open
so that he can breathe. His eyes aren’t important,
but just so you know it’s a person. So this is my test subject
or the person I’m going to use to diagram. That’s his ear. Maybe he has a bit of a– let’s
give him some hair. All of that is irrelevant,
but this is our guy. This is the guy that’s going to
show us how we take air in and how we take air
out of the body. So let’s go inside
of this guy. I can draw his outside
first. Let me see how well I can do this. So this is outside the guy. That doesn’t look right. Let’s say the guy looks
something like this and he’s got– this is his shoulders. That’s our guy. All right. So in our mouth, we have our
oral cavity right there, which is just the space that
our mouth creates. We have our oral cavity. I could draw our tongue and all
of that and maybe I will. Maybe I’ll draw the tongue. But you have this space inside
of the mouth– call that the oral cavity. Oral for mouth, cavity for
space, or hole, or opening. And then also you have your
nostrils and they open up into a nasal cavity. So that’s another big space
just like this. And we know that they connect at
the back of our nose or the back of our mouth. And this passage right here
where they connect is called the pharynx. When your air goes through your
nose– they say breathing through your nose is better,
probably because it gets filtered by your nose hairs and
it gets warmed up and and what not, but you can breathe
through either side. The air goes in through either
your nasal cavity or your oral cavity and then comes back
through your pharynx and then the pharynx splits
into two pipes. One for– well, one, air can
go down either one, but the other one is for food. So your pharynx gets split. In the back you have your
esophagus– and we’ll talk more about the esophagus
in a future video. In the back you have your
esophagus and in the front– let me draw a little dividing
line there. In the front, maybe this– let
me make it connect like that. I was using yellow. I’m going to use yellow to
continue and I’m going to use green for the air. So it divides just like that. So behind your air pipe, you
have your esophagus. Let me make that
another color. And then right here
is your larynx. And I’m going to concern
ourselves with the larynx. Esophagus is where your
food goes down. We know that we eat food
with our mouth as well. So this is where we
want our food to go– down the esophagus. But the focus of this video
is our ventilation. What do we do with our air? So I’m going to focus as the air
goes through our larynx. And the larynx is also
our voicebox. So as you hear me talking right
now, there are these little things right about here
that are vibrating at just the right frequencies and I’m able
to shape the sound with my mouth to make this video. So that’s also your voicebox,
but I won’t focus on that right now. It’s called a voicebox because
of this whole anatomical structure that looks something
like that. But then after the air passes
through the larynx– this is on the way in– it goes to the
trachea, which is essentially just the pipe for air. The esophagus is the
pipe for food. Let me write this down. And then from the trachea– and
the trachea is actually a reasonably rigid structure. It has cartilage around
it and it makes sense that it has cartilage. You don’t want– you can imagine
a hose– if it bent a lot, you wouldn’t be able to get
a lot of water through it, or a lot of air through it. So you don’t want this
thing to bend a lot. So that’s why it needs to have
some rigidity– so that’s why it has cartilage around it. And then it splits into two
tubes– and I think you know where these two tubes
are going to. And I’m not drawing this
in super detail. I just want you to get the idea
of them, but these two tubes are the bronchi– or
each one is a bronchus. And they also have cartilage,
so they’re fairly rigid, but the bronchi keep splitting. They keep splitting into smaller
and smaller tubes just like that and at some point,
they stop having cartilage. They stop being reasonably
rigid, but they keep splitting off. So I’ll just draw them as
these little lines. At some point they become
such thin things. They just keep splitting off. So the air just keeps splitting
off and spread and goes down the different paths. And when the bronchi no longer
have cartilage around them, they’re no longer rigid. The first of those are called–
or actually all the tubes after that point are
called bronchioles. These are bronchioles. So for example, that we could
call a bronchiole. And there’s nothing
fancy here. It’s just a pipe that
just gets thinner and thinner and thinner. We’ve labeled the different
parts of the pipes different things, but the idea is, let’s
take it through our mouth or our nose and we just keep
dividing and keep dividing this main division into two
different paths that takes us into each of our lungs. Let me draw this guy’s
lungs here. And these bronchi– or the
bronchi split into the lungs– the bronchioles are in the
lungs and eventually the bronchioles terminate. And this is where it
gets interesting. They keep dividing smaller and
smaller, thinner and thinner and thinner, into these little
air sacs, just like that. At the end of every super small
bronchiole are these little air sacs– super small
air sacs– and I’m going to talk about these air
sacs in a second. And these are called alveoli. So I’ve used a lot of
fancy words, but the general idea is simple. Air comes in through a pipe. The pipe gets thinner and
thinner and thinner and they end up at these little
air sacs. And you’re saying, well,
how does that get the oxygen into my system? Well, the key here is that these
air sacs are super small and have very, very, very
thin walls– or I guess thin membranes. So let me zoom in. So if I were to zoom in on one
of these alveoli– and just to give you an idea, these are
super duper duper small. I’ve drawn them fairly large
here, but each alveoli– let me draw a little bit bigger. Let me draw these air sacs. So you have these air
sacs like this. And then you have a
bronchiole that’s terminating in that air sac. Maybe a bronchiole is
terminating in another air sac just like that– another set
of air sacs just like that. Each of these are only 200 to
300 microns in diameter. So that distance right there–
let me switch colors– that distance right there is
200 to 300 microns. And in case you don’t know what
a micron is, a micron is a millionth of a meter–
or you can view it as a thousandth of a millimeter. So this is 200 thousandths
of a millimeter. Or you can think of them as–
and this is actually a very easy way to visualize it– this
is about one fifth of a millimeter. So if I actually try to draw it
on the screen– if you made this full screen, a millimeter
is about that far. Maybe a little farther
than that. Maybe about that far. So imagine a fifth of that and
that’s what we’re talking about the diameter of
one of these things. And just to put it in the
whole scheme relative to cells, the average
cell in the human body is about 10 microns. So this is only about 20 or 30
cells in diameter or relative to the average cell
in the human body. So these have a super
thin membrane. If you view them as balloons,
the balloon is very thin– pretty much one cell thick and
they’re connected to the bloodflow– or actually, a
better way to think about is that our circulatory system
passes right next to each of these things. So you have blood vessels that
come from the heart and they want to be oxygenated. In general, the blood vessels
that don’t have oxygen– and I’m going to do this in a lot
more detail when I make the videos about the heart and our
circulation system– the blood vessels that don’t have oxygen–
de-oxygenated blood is a little bit darker. It looks a little
bit purplish. So I’ll draw it as blue. So these are vessels that are
coming from the heart. So this blood right here has no
oxygen in it or it’s been de-oxygenated or it has very
little oxygen in it. And the word for the blood
vessels that comes from the heart are arteries. Let me write that down. I’ll review that again when
we cover it in the heart. So arteries are blood vessels
from the heart. And you’ve probably
heard of arteries. Vessels that go to the heart
are called veins. This is really important to keep
in mind because later on, you’re going to see that
arteries don’t always carry oxygen or they’re always not
de-oxygenated and veins always aren’t one way or the other. We’re going to go into a lot
more detail when we actually cover the heart and the
circulatory system, but just remember, arteries go away. Veins go to the heart. So here, these are arteries
going away from the heart to the lungs, to the alveoli
because they want the blood that’s traveling in them
to get oxygen. So what’s going to happen is
that the air is flowing through the bronchioles and
circulating around the alveoli, filling the alveoli–
and as they fill the alveoli, the little molecules of oxygen
are allowed to cross the membrane of the alveoli
and essentially be absorbed into the blood. I’ll do a lot more on that when
we talk about hemoglobin and red blood cells, but you
just have to realize that there’s just a lot
of capillaries. Capillaries are just super small
blood vessels that allow air to pass– essentially oxygen
and carbon dioxide molecules to pass
between them. These have a lot of capillaries
on them that allow the exchange of gases. So the oxygen can go into this
blood and so once the oxygen– so this is the vessel that’s
coming from the heart and then it’s just a tube. So then once it gets the oxygen,
it’s going to go back to the heart. And so essentially this is the
point where this vessel, this pipe, part of our circulatory
system, goes from being an artery– because it’s coming
from the heart– to a vein because it’s going back
to the heart. And there’s a special word for
these arteries and veins. They’re called pulmonary
arteries and veins. So going away from the heart to
the lungs, to the alveoli, these are the pulmonary
arteries. And going back to the heart
are the pulmonary veins. Now you’re saying, Sal, what
does pulmonary mean? Well, pulmo comes from the
Latin for the lungs. It literally means the arteries
that are of the lungs or that go to the lungs
and the veins that come from the lungs. So anytime people talk about
pulmonary anything, they’re talking about our lungs– or
maybe something related to how we breathe. So it’s a good word to know. So anyway, you have your oxygen
coming in through your mouth or your nose, through the
pharynx– it could fill your stomach. We can blow up our stomach
like a balloon, but that doesn’t help us actually get
oxygen to our blood stream. But the oxygen will come through
our larynx, into our trachea, through the bronchi,
eventually in bronchioles, ending up in alveoli and being
able to be absorbed into what where the arteries, but then
we’re going to go back and then essentially oxygenate
the blood. The red blood cells become red
once the hemoglobin becomes very red or scarlet once it
actually has the oxygen and then we go back. But at the same time, this
isn’t just about getting oxygen into our arteries
or onto the hemoglobin. It’s also about releasing
carbon dioxide. So these blue arteries coming
from the lungs are also going to release carbon dioxide
into the alveoli. And these will be exhaled. So we have oxygen coming in. Other things will be coming in,
but the O2 is what gets absorbed in the alveoli. And then when we breathe out,
we’re going to have carbon dioxide that was in our blood,
but then it gets absorbed into the alveoli and they
get squeezed out. I’m going to tell you in a
second how it gets squeezed. It’s actually that squeezing out
that actually– when the air goes back out, it can
vibrate my vocal cords and it’ll allow me to talk, but I’m
not going to go into too much detail about that. So the last thing to consider
about this whole pulmonary system or about our lungs is,
how does it force the air in and how does it force
the air out? And the way it’s done is really
kind of like a– you could imagine it’s kind of a
pump or a balloon– is that we have this huge layer
of flat muscles. Let me pick a good color here. Right below the lungs–
and this is called a thoracic diaphragm. And so when it’s relaxed, it
kind of has this arch shape, and so the lungs are kind
of squeezed in. They don’t have a
lot of volume. But when I essentially breathe
in, what’s happening is this thoracic diaphragm is contracted
and when it’s contracted, it gets shorter, but
more importantly, it opens up the space where
my lungs are. So my lungs can fill
up that space. So what it does is, it
essentially– it’s like pulling a balloon larger,
making the volume of my lungs larger. And when you make the volume of
something larger– so the lungs will become larger as
my thoracic diaphragm is contracted and it kind of arches
down, creates more space– and as the volume of
something becomes larger, the pressure inside of
them goes down. If you remember from physics,
the pressure times volume is a constant. So when we breathe in, our brain
is essentially telling our diaphragm to contract. We have more space
around our lungs. Our lungs expand to
fill the space. We have less pressure here than
we have outside– or you can view it as negative
pressure. So air always wants to go from
high pressure to low pressure and so air is going to
flow into our lungs. And hopefully there’ll be some
oxygen there that can then essentially go into our alveoli
and end up in our arteries and then go back in the
veins as oxygen attached to hemoglobin. I’ll talk more about
that in detail. And then when we stop
contracting the diaphragm, it goes back to this
arched position. It contracts. It’s kind of like
a rubber band. It contracts back the lungs and
it essentially expels the air back and now that air’s
going to have a lot more carbon dioxide. And just to get a sense of– I
can look at my lungs– I can’t look at them, but they
don’t seem too large. How do I get enough oxygen in
them– and the key is, is that because of this branching
process and the alveoli, the inside surface area of the lungs
are actually much larger than you can imagine– or
actually than I could have imagined had someone
not told me. So it actually turns out– I
looked it up– the internal surface area of your alveoli–
so the total surface area where the oxygen can be absorbed
in or the carbon dioxide can be absorbed out from
the blood– it’s actually 75 square meters. That’s meters, not feet. If you think about it, that’s
like a– imagine some type of a tarp or a field. That’s almost nine
by nine meters. That’s almost 27 by
27 square feet. That’s the size of some
people’s backyards. That’s how much surface air you
have inside of your lungs. It’s all folded up. That’s how it gets jammed into
what look like relatively small lungs. But that’s what gives us enough
surface area for enough of the air, enough of the
oxygen, to cross the alveoli membrane into our blood system
and enough of the carbon dioxide to go back in. And just to have a sense of how
many alveoli we had– I told you that they’re very
small– we actually have 300 million in each lung. In each lung, we have
300 million alveoli. So anyway, hopefully that gives
you a decent sense of how we at least get oxygen
into our blood system and carbon dioxide out of it. In the next video, I’ll talk
more about our actual circulatory system and how we
get the oxygen from the lungs to the rest of the body and
how do we get the carbon dioxide from the rest of the
body into the lungs?

100 thoughts on “The lungs and pulmonary system | Health & Medicine | Khan Academy

  1. I really enjoy learning from your videos. I wish I could have more teachers that can keep my focus and make learning fun like you do. Thanks =)

  2. Wow, I have been reading this chapter in my paramedic book about the pulmonary system and didn't get it at all, watched this video and it all makes perfect sense now. This dude is awesome.

  3. I'm a nursing student at Conestoga College and just want to say thank you so much for your awesome videos, I just subscribed to your channel and can't wait to watch the videos that make everything so much easier to understand cuz of your fantastic animations. Thanks for all the time and hard work you put into these videos

  4. I am also a nursing student and not only did you help me get an A in microbiology and get into the program, but now you're helping me through the program! You are an amazing teacher and immensely talented. Just as Albert Einstein said "if you can't explain it simply, you don't understand it well enough." You explain everything so simply and I thank you so so much! You are great, Sal!

  5. You're an idiot go back to in time and they'll probably like you more in the dark ages lol As for in the year 2013 we don't like you

  6. Being a british person, its painful to see you spell oesophagus as "esophagus". I do hate the spelling and pronunciation differences between England and America, it adds too much confusion.

  7. I'm studying here as a medical student in sweden, coming from the states i have to learn everything in swedish, but omg, u have described everything in such a way that i can explain it in my own words in swedish! U are awesome! thanx for the wonderful lecture!

  8. i'm studying in medical school in the UK and i hate how the English spell esophagus with an O ! along with their other absurd spelling tactics,and I always get shit from my doctors for my american spelling and pronunciation.they even deducted my mark for it!

  9. I'm a third year Microbiology student and Khan Academy has not only helped me pass but achieve my aim of coming first in every class for the past two years. Not only that, I'm a teacher's pet because I'm always the first to understand any new concept and am able to help my fellow classmates(they don't know my secret of course, feel guilty about it…sometimes). Anyway, thank you Mr.Khan and the entire Khan faculty.

  10. Thanks for posting. Taking online classes is not easy – it all depends on the ability to read and understand the text books, which many times are so confusing.

  11. Thank you so much professor khan!!!!Before each exam for my anatomy, I watch one of your video.Thanks again!!! From Seydou New Jersey, usa

  12. Why is the alveoli looks like grapes when it use purple color to draw out😂😂 And this helps me a lot with my exam coming in January TYSM Khan Academy

  13. While watching these videos I was also thinking about my brain how did it know to do all these stuffs. It's really fascinating and I think I will have sleepless night now.

  14. I am so grateful for this page. I am studying for my NASM CPT exam, and even though they provide good resources for us to learn with, I like to push my understanding further. its awesome that this person takes the time to make these videos. I commend you and sincerely thank you!

  15. THANK YOU SO MUCH! My teacher did such a poor job teaching me, and your videos really helped me understand! This is really going to help me get through biology.😊

  16. Thank you so much! I would get an A+ in your class. My teacher sucks and am stuck with B. However, I think am gonna do better in tomorrow's exam!

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