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

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

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

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

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

you take a deep breath through your mouth.

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

and then you take that one through your nose.

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

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

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

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

it almost follows an identical path.

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

So here we have air coming in from the nose,

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

because the heart is literally kind of peeking out here.

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

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

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

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

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

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

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

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

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

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

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

and it basically becomes the floor.

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

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

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

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

And this entire room we actually call the thorax.

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Now I know it looks a little bit strange because

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

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

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

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

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

but of course that middle lobe does go back.

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

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

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

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

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

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

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

And these sacs, we call these alveoli. Alveoli.

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

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

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

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

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

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

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

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

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

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

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

gets breathed into the lungs when you inhale,

gets down into the alveoli, exchanges with the blood;

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