Now, let's get into the cells. I don't know what you thought about in microbiology,
in cellular biology, but I promise you, this is gonna be worth your investment of time.
So we've got three types of alveolar cells.
First there's pneumocytes, there's a Type I and a Type II, yes, fairly disappointing, don't you think?
Like could you not have come-up with a funner name than Type I or Type II?
Alright, I'm not trying to be critical but these people could never work in a lipstick factory
cuz it just wouldn't fly, but pneumocytes are Type I and Type II
and these are found right in the alveolar wall.
Now, these maybe new to you now but they're going to be old friends
by the time we finish with this video series.
So Type I, Type II, look how they appear different.
Type I look like the ballet dancers, right, they're long, they're graceful.
Then look at the Type II? More like my speed, kinda cuboidal, short and thick,
there you go, that's what you got going.
For now, I want you to visually picture how they look different.
You can see if you're designing a wall that we're gonna have a lot more Type I's that are in there.
Okay, so these are in the alveolar wall, that's where we find them,
the other one are the macrophages, they look kinda of -- kind of ominous but they're phagocytic cells.
Okay, these are immune cells and they move around in the lumens of the alveoli
and in the connective tissue between them.
Yeah, that's right, we have connective tissue in your lungs, I think that is so cool.
We usually think of connective tissue as joints and muscles,
but, no-no, you got it in your lungs, too.
So these macrophages, they're phagocytic, that means they can absorb things.
But they're part of your immune system, and where are they found?
Well, they're moving around in the lumens of the alveoli and in the connective tissue in between them.
So those are the three type of cells, pneumocytes and macrophages.
We've got two types of pneumocytes so they're, I know,Type I, Type II.
Which one were the more elegant? Right, Type I.
Which one are more like me? Type II, you got it.
So those are the two types of pneumocytes plus we have macrophages,
these are the phagocytic cells that are part of your immune system.
So if you're at dinner tonight and someone says,
"Hey, does anyone know the three types of alveolar cells?"
You say, "Well, yes, I do. There's two types of pneumocytes, Type I and Type II,
and there's also macrophages which happened to be phagocytic cells."
If it comes up, you email me and let me know.
Now, let's look at the alveolar wall. Is this not amazing?
Now, you've seen the picture on the left, right?
You know that that's the alveolus, you see the air comes in, oxygen comes in at the top,
it's gonna hit the bottom of the alveoli where the capillaries are all wrapped around,
that's where the exchange is going to happen.
But look what we gave you over on the right-hand side.
See, we're showing you one alveolus.
If you've got 600 million of these guys in your body,
you gotta know they are packed in tight, close together.
So that's why we gave you this cut-away picture.
So this, you're kinda looking at the side, if we sliced it, that's the picture on the left.
Look over here on the right, see how close those capillaries are?
See how close and tight together those alveoli are?
That's why we wanted you to have that graphic and by the way that is a gorgeous picture.
This is the one, of the ones I have on my wall because I just love what it shows.
Now, see what you've already learned.
You see that up, yeah, there's the capillaries, right, you can compare it to the picture on the left,
okay, that make sense. Do you see the macrophages?
Yeah, see them right in there? Cool. Do you see the alveolar wall?
Yeah, the picture on the right, you see where the alveolar wall is
and then compare that to the picture on the left.
See, when you do this kind of exercises with your brain, you don't ever want to waste a picture.
First of all, somebody spent a lot of time creating it for you,
whether it's in a textbook or you see one of the pictures I have for you here in the video,
so this means we intentionally chose specific items we wanted
to help you with better understanding of your patient's body systems.
So stop, pause, take a look at them and make sure they make sense to you.
Look at them from different angles, compare one picture to another picture,
I promise you, it will super charge your studying and understanding physiology.
Now, I wanna talk about surfactant, it's essential.
So I wanna spend some time with you explaining how it works.
So what have you heard about surfactant?
When I say that, what has been taught to you before,
what did you learn from your physiology courses?
What do you already know about it?
Okay, just right some quick notes to yourself in the margin.
Okay, so back to Type I and Type II.
Type I or squamous alveolar cells, right, they're squamous,
they're extremely thin, they cover about 95% of the alveolar surface.
Now, these are the ones that are involved in gas exchange.
Remember, they're the lovely ones, they're the elegant ones,
they are the thin and beautiful ones, there you go, right there,
Type I's, they're the guy that do the oxygen and CO2 exchange.
Now, the Type II are great alveolar, right, they're granular, they're roughly cuboidal,
they cover only about 5% of the alveolar surface.
Now, these are the guys that, they secrete pulmonary surfactant.
Hey, without this you wouldn't make it.
So these might not be the most attractive when you compare them with the Type I's
but they're super important to your survival.
Okay, take a look at this graphic.
Now, most of this you have seen before,
but I wanna check your powers of observation, your assessment.
What is different about this picture than when you've seen it before?
Have you found it yet? Right, it's the surfactant layer. Everything else is the same.
You've got the alveolus, you've got the single-cell wall,
we've got the capillary, we've even got the airway up there with the big sack of them,
all of that you've seen, but what's different here is what's critically important, it's the surfactant layer.
Now, remember, surfactant is produced by the alveolar Type II cells, right?
Those Type II cuboidal cells, they're the ones that produce surfactant.
Now, it's made up of lipids and proteins, that's really important
because as some of it is special properties, we'll get to more of that in a little while.
But surfactant maintains the structural integrity of the alveoli.
So see we've got it kinda of all the way around there, it's what helps keep the walls open
so it doesn't collapse, because I'm telling you, maintaining structural integrity
may seem like an odd word choice but the opposite of structural integrity is collapse of the alveoli,
and a collapsed alveoli is one that cannot exchange CO2 and O2, so it's of no use to its owner.
Now, surfactant decreases the surface tension and increases lung compliance.
Check, I know you've heard that before.
You've heard in your physiology courses, you know it.
Yep, decreases the surface tension, increase lung compliance, blah, blah, blah.
Yeah, but I wanna take you a couple steps deeper cuz I want you to understand,
what does surface tension have to do with an alveoli?
What does lung compliance have to do with surface tension
and what role does surfactant play in that?
Tell me, this is gonna be really fun, so stick with us.