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Let's say that this is you. You're enjoying a nice sunny day

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and you decided to take a nice long deep breath of air.

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And of course when I say air the part that you 
probably care the most about is just the oxygen,

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part of that air, that's the part that 
we as humans need to survive.

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So you take a deep breath. 
Let's say you take it through your mouth,

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you take a deep breath through your mouth.

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And then lets say you take one more deep breath, 
a second deep breath,

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and then you take that one through your nose.

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And you might think, "Well, these are two totally 
different ways of getting in air."

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That's certainly how it looks when 
you look at the mouth and nose.

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They don't look like they have much in common.

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But the truth is that actually if you follow the air,

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it almost follows an identical path.

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The air is gonna go into the back of the throat 
really regardless of how you took it in.

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So here we have air coming in from the nose,

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in here yet air coming in from the mouth 
and they meet up in the back of throat.

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And then they go down down down,
they go towards this thing that we call the Adam's apple.

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I'm gonna bring it up a little bit, you can see it more easily.

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But basically you bring up this, you see 
this Adam's apple right there.

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And actually you can go ahead and 
take a feel of you own Adam's apple.

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It's a pretty cool structure in the middle of your throat

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and everybody has it, that's the first thing I want to tell you,

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that everybody has it, not just men, women have it too.

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And the reason it's called an Adam's apple 
is because "Adam" is generally a boy's name.

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And so it's to remind us that usually men or boys 
have larger Adam's apples than girls.

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And if you're trying to find it, 
I also want to point that it's a notch here.

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And you if you can feel the notch with your fingers,

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in that case you have a nice clue as to where it is located.

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This is Adam's apple and what it does is, 
it helps you control your voice.

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And actually there's another name for Adam's apple.

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Another name for it, sometimes 
people call it the voice box. The voice box.

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And of course air is passing through the voice box 
in this kind of the entry way into the trachea.

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And so it actually allows me to make my voice 
very high or make my voice very low,

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depending on how you change 
the muscles around in that Adam's apple.

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So that's actually kind of a first cool thing I want to point out to you, that you can actually control your voice.

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I'm sure you knew this already but what you're using 
is the Adam's apple, your voice box.

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Now air keeps going, air is just gonna 
keeps making its journey down and

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specifically of course the part of air I said, 
you know, we care about is the oxygen.

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It's gonna keep making its journey 
down into the lung areas,

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now the lung areas, it's gone down the trachea and it goes into the two lungs, the right and left lungs.

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This is the left lung, I'm gonna put L for left 
and this is the right lung, I'll put R for right.

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And immediately you'll think, 
"Wait a second, aren't they switched?"

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Now I want you to remember that this is from the perspective of the person who owns the lungs.

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So that's why I put it in left where I put it, 
in right where I put it.

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Now we should probably go ahead and 
start labelling some of these.

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You can see that the lungs actually 
don't look identical, right?

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They look slightly different, for example, 
this one has three lobes.

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The right side has three lobes called 
the upper lobe, middle lobe and lower lobe.

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And the left one only has two lobes, 
that's the first kind of a big difference.

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And the other difference is that you actually have 
this thing in the middle that we call a cardiac notch.

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This thing right here, this is called the cardiac notch.

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And the reason we call it that is that 
it's a little spot that gets formed

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because the heart is literally kind of peeking out here.

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And as a result it's kind of makes a notch 
in the lung where it develops.

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So the heart takes a little space here, this is the heart.

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And as a result, it takes or makes that notch. 
So this is our heart space there.

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So on the other side you've got of course 
your two lobes, your upper and lower lobes.

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And these are exclusive, you see a lung 
that's kind of sitting by itself.

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And you want to figure out whether 
it's the left lung or the right lung,

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you can look for the lobes, the number of lobes, 
or you can look for that cardiac notch.

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Now around here, around these lungs, you've got ribs.

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You've got ribs here and between the ribs 
you've got rib muscles and of course on both sides.

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And below the lungs and below the heart, 
you've got a muscle, a big muscle.

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Actually it's gonna come through here, 
I'm just gonna kind of go through the word heart,

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and it basically becomes the floor.

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So the heart and the two lungs sit on this floor 
that made up of this muscle

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and this muscle is the diaphragm muscle. 
So this diaphragm muscle makes up the floor;

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the ribs make up the walls. So what do we have?

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We have basically a room, we have a giant room 
with walls and the floor.

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And this entire room we actually call the thorax.

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So within this room then you have 
your two lungs and your heart.

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So, so far so good, but I haven't done a very nice job 
of actually showing you where the air goes.

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I just kind of pointed that it goes to the two lungs, 
we don't have to get to see where it goes after that.

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So let me actually, I'm gonna erase a lot of these.

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I’m gonna reveal to you what it would look like. 
If you could slip on some X-ray glasses

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and look into your two lungs, 
this is kind of what it would look like.

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You've got all these interesting architecture and 
the easiest way to kind of think about this,

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probably the simplest way to think about this, 
is to imagine a tree,

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to imagine a tree, and that tree 
has been flipped upside down,

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so you've got all these branches of that tree 
and they are branching and branching.

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And if you flip this tree upside down, you start seeing that it looks a lot like what we have in our lungs.

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Our lungs basically look like a flipped up or 
a flipped upside down tree and we even call that,

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we even call this entire structure, 
we call it a bronchial tree.

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So when you look at the lungs and 
they look kind of messier and complicated.

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Just think of them as an upside down bronchial tree 
and all of a sudden

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it'll look much simpler with basically 
in the middle you've got this nice trunk,

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this is our trunk, and then it's kind of 
branching from there.

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So air goes down this main trunk, this trachea, 
and they kind of start splitting up.

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And each of this kind of colored regions, the green region and the purple region serve a different lobe.

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So this green region serves the lower lobe down here, 
the purple serves the upper lobe.

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And on this side, you've got an upper, 
a middle and a lower lobe.

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Now I know it looks a little bit strange because

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you’ve got some green branches in what should be 
the middle lobe like right here;

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you've got some orange branches in what 
looks like the upper lobe like right there.

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But what you have to remember, this is kind of tricky, 
just try to play it in you head,

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what you have to remember is that, what you have 
is basically a three dimensional lung.

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So you have to imagine that we are literally 
looking at the front side,

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but of course that middle lobe does go back.

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And if you went back then you'd make perfect sense
why the orange branches are where they are at.

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Now let me continue the air journey because 
I wanna make sure we finish it off.

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So let's say we take a little branch like that, we expand it.

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We keep zooming into it, zooming into it, zooming into it,

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until it's microscopic, you cant see it 
with your eyes any more;

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but you could see it under a microscope. 
It would look like this.

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It would basically in a microscope, 
it would look like a bunch of little sacs like these.

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And these sacs, we call these alveoli. Alveoli.

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And the air, it actually kind of runs into the alveoli.

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It has a dead end and then it comes back around.

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And then you breathe it out. So that's how breathing works.

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The air goes all the way from the mouth down 
to the alveoli, takes a U-turn and it goes back out.

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But before it does that, before it leaves-
Very close to the alveoli is blood.

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Let's say blood is coming this way and going that way, 
and what will happen is that,

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actually out of the or into the blood, let's do that first.

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We've got oxygen, oxygen will actually go into the blood, and out of the blood will be waste.

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So you'll have some carbon dioxide waste 
that your cells have been making.

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And that waste actually then 
gets thrown back into the alveoli.

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So now you can see how oxygen 
gets from the outside world,

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gets breathed into the lungs when you inhale,

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gets down into the alveoli, exchanges with the blood;

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and then you exhale and let all that carbon dioxide out.