Hi. It's Mr. Andersen. Welcome to my podcast on the Respiratory System. The
function of the respiratory system is basically to take in oxygen and then get rid of carbon
dioxide. And right here in Montana at around 5,000 feet that's no big deal. But if I were
to climb Mount Everest, the higher I go the less oxygen there's going to be. And that's
a real limit to our ability to climb very high. And so it wasn't until 1953 that Sir
Edmund Hillary and Tenzing Norgay finally climbed Mount Everest for the first time.
And you can see Tenzing Norgay right up on top. The first photo ever taken from the top
of Mount Everest. And it wasn't until 1953, but if you can't see on his back there's a
huge canister that contains oxygen. And that leads into his mouth because they had to take
oxygen with them. And so it wasn't until I think 1971 that somebody was able to climb
all the way up Everest without using oxygen. And they do that by going up to a base camp,
move up higher, move down, move higher, move down, move higher, move down. And so their
body is starting to accommodate to that change in the elevation. And even that you're pretty
much dying at the top because of that lack of oxygen. And so basically animals have figured
this out a number of different ways. If you're a worm, your respiratory surface is actually
going to be your skin. You're absorbing oxygen and getting rid of carbon dioxide through
your skin. So their skin has to be moist. And they have to have a large surface area.
If you're an insect you use things called spiracles. So basically there are holes on
the side of an insect that go to tubes. That go to more tubes and more tubes and more tubes
and more tubes. And an insect actually has tubes that almost go all the way down to the
level of cells. And so you have to have a huge surface area is one thing you need. And
then it has to be moist in another thing you need. And so the two big things I want to
talk about are gills. So gills is a way that fish have solved this problem. And then lungs.
And that's the way we've solved it. And so what's the difference between fish and us?
Well fish live in an area that's really, really moist. So they don't have to worry about that.
And so their gills just sit right out in the water. But they also live in an area where
there's not much oxygen at all. And so they have to have a very efficient way of exchanging
oxygen. Us, well we have to fold our lungs inside our body so we can keep them moist.
But there's so much oxygen in the air relative to the amount that's in the water that we
don't have to be as efficient. So how efficient do the gills actually have to be in fish?
They can reclaim something like 80% of the oxygen that's in the water. So they're really,
really efficient. We're not even close to that. And the way they do that is they use
something called countercurrent gas exchange. And so basically as the blood flows through
the gills, the blood is going to flow like this. So all the blood is going to flow in
this direction. And then it's going to flow out the other direction. So in the gills it's
going in that direction. Then it comes out in the other direction. But the water is going
to flow in this direction. And so what you have is the blood flowing in this direction.
And then you have the water flowing counter to that. And so as they go like that, it pulls
water in over their gills. But the blood is moving in opposition to that. Engineers use
countercurrent exchange quite a bit. But basically what is it doing? Well if you think about
this, this is going to be the dirtiest of blood down here. And then it's going to get
cleaner and cleaner. In other words it's going to get more and more oxygen. But what it's
doing is as it gets more and more oxygen, it's meeting water that's more and more fresh.
In other words it has more of the oxygen present. And so by putting blood in the opposite direction
they're really efficient at getting that oxygen outside of the water. Now us, we don't have
that problem. We do have a problem with moisture. And so we actually have to fold our gills
inside our body. They're not gills, but we fold our lungs inside our body. And so we
have a trachea that leads down into bronchus and then bronchioles, all the way down into
the alveoli. One thing that's important to note is that it goes in and then that's it.
In other words it's one way flow. When we breathe in, it goes in. And then that's the
end of it. And so if you take things in, like if you smoke, all the material that comes
in is going to go into your lungs. And then there's no out. And so if you breathe a lot
of coal dust, it's going to go in and then it gets stuck in there. Or asbestos goes in
and gets stuck. And so the lining of the trachea, the lining of our respiratory system have
these cilia on them. And so basically what happens is those little hairs are going to
move material out of your body so you can cough it up and eventually swallow it. Another
cool thing about this is that it really looks, let's even go to this level, it almost looks
like a tree upside down. And so basically what's happening is that we are increasing
the surface area by having the trachea go to the bronchus and then the bronchioles.
And then they just keep branching and branching and branching. Again why are they doing that?
They're doing that to increase the surface area. And so your lungs are small. But I remember
once reading that they have the surface area of a tennis court. And so by having that large
surface area we can absorb even more oxygen. But the functional units of the lungs are
the alveoli. So if we get way to the end of these tiny bronchioles we eventually have
these little sacs. They're called alveoli. They're covered in a single layer of cells
called simple squamous cells. And they have a tendency to just kind of fold in. Imagine
a tiny balloon, that small. It would just kind of fold in on itself. And so they have
to have these chemicals called surfactants on the inside that kind of lubricate it so
it doesn't close up. That's one of the reasons why premature babies have to be in a ventilator
because they haven't really developed that surfactant yet. But wrapped around all of
the alveoli we have these capillaries. And so basically what's happening is that we're
taking oxygen from the alveoli and we are passing that off on to these capillaries.
And then we are getting rid of carbon dioxide. That's the function of the alveoli. Now how
does breathing occur? Breathing occurs using the diaphragm muscle. You've dealt with the
diaphragm if you've ever had the hiccups. Because that's just a spasm in the diaphragm
muscle. But basically what happens is we have the diaphragm muscle here. And then as that
contracts and pulls down then we have air moving in. So it's like you had a jar with
a balloon on the inside of it with rubber on this side. And if I were to pull right
here. If I were to pull that down, basically it's going to inflate the balloon because
air is going to move in through here. So I decrease the pressure. And then as I relax
the diaphragm it's going to go like that. And as I contract the diaphragm it's going
to move up like that. It's very important that then, just like this jar, that this is
very intact here. We have to make sure that this whole thoracic cavity is intact so we
can create that pressure. Okay. So let's get to the level of that oxygen exchange. So how
do we get oxygen in? Well basically if you were to look here in the capillaries, let's
imagine that this out here is the space in the alveoli. So now we have air coming in.
So we have air out here. Basically what's going to happen is these red blood cells,
as they move through the capillaries, that oxygen that's inside the alveoli is going
to move in. And so these red blood cells are almost in direct contact with the capillaries.
Now where is the oxygen going to be stored? We have a chemical called hemoglobin. Hemoglobin
is a protein and that's stalk full inside all of our red blood cells. That's why it's
red. So basically inside the hemoglobin we have these iron molecules. One there, one
there, one there, one there. And that iron is going to bond to the oxygen that's found
inside the air. And so why is it red? It's because it literally is rusting. The oxygen
is attaching to the iron and it's giving us that red color. And so that's where the oxygen
is going to bind. It's going to bind to that heme group or the iron inside the hemoglobin.
What about the carbon dioxide? Well the carbon dioxide is not really contained within the
red blood cell itself. Basically what it's doing is it's being converted to bicarbonate.
So we're converting that carbon dioxide with water to this bicarbonate. And a lot of that
bicarbonate will actually be right here inside the plasma of the blood. Some of it will be
in the blood cell, but most of it's in the plasma. When we get here to the alveoli we've
got enzymes that control all of this. Then that's going to release as carbon dioxide.
So carbon dioxide goes back into the alveoli. And we breathe that out. We take in more oxygen
over and over and over again. And so that's the respiratory system. It doesn't work if
we don't have a circulatory system, but we'll get to that in the next podcast. And I hope
that was helpful.