The bronchial tree | Advanced respiratory system physiology | Health & Medicine | Khan Academy

The bronchial tree | Advanced respiratory system physiology | Health & Medicine | Khan Academy

November 8, 2019 52 By Kody Olson


So here’s a little person,
and I’ve drawn their face, and you can see in blue at the
bottom I’ve drawn their voice box, and I’m going to show you
exactly what happens when you draw a little molecule
like this of oxygen and to follow it
along it’s journey. So it’s going to be breathed
in either through the nose or through the mouth. And you know it’s going to kind
of end up in the same place or so we think, right? We said that basically kind
of the back of the throat is where it’s going
to end up, and this is my nose kind of going
in the back of the throat, and the mouth kind of
empties into the same spot. But already, there are going
to be some differences. So for example, you have in your
nose, these little yellow nose hairs, and the first
question, of course, people think of
with nose hairs is what the heck is their purpose? What do they do? And nose hairs are part
of our filter system, so we have this great filter
system and there’s nose hair, and their job is to
make sure that all of the kind of large
particles of dirt and dust are kind of picked up. So they’re good for getting
all the large particles out of the air so it’s cleaned up. Then you also have this
green slime, right? this kind of green mucus
that we all kind of make, and this mucus sometimes,
you think of it as snot, this snot or mucus
is good for small particles, because it’s really sticky, and
this small particles of dust and dirt are going
to glom onto it, and so that is our way of
kind of cleaning up the air so that when we breathe
in through our nose, the air is basically
clean or at least cleaner than it would be otherwise. And so of course, if you
compared nose air or the air that you breathe in through your
nose to air that you breathe in through your mouth,
the mouth air will be, of course
a little dirtier, because they didn’t have
that nice filter system. And kind of thinking
along the same route, if you think about picking your
nose, that would be basically kind of cleaning
the filter, right? So that’s kind of
a new way maybe of thinking about that habit. So air is going to end up going
to the back of the throat. So air is going to
kind of go in this way, and a little
molecule of oxygen is going to kind of end up
at the back of the throat. And another kind of
interesting difference is that already, that oxygen
molecule and the air around it is going to be slightly
different in other ways. It’s going to be cleaner if
it went through the nose, but either way, nose or
mouth, it’s going to be warmer and also more moist. So that’s another change. In comparison, on
the outside, the air is a little colder and drier. So these are some
key differences in terms of what’s
happening to the air. These are two major
differences, right? So now the air or little
molecule of oxygen has got a choice. It can either go kind of
down one of two paths. One, I’m going to draw is
going to be into the larynx. This is our larynx right here. And we also call our
larynx our voice box, so you might remember that
was the name I had mentioned previously, voice
box, or larynx, is kind of the more
medical word, I guess. And sitting over the
larynx is the epiglottis. And the epiglottis is
basically like a lid kind of protecting the
larynx from making sure that food and water
don’t go into it. Now, there’s another
tube I just alluded to, and it’s sitting right
here, and this purple tube, is our esophagus So the
esophagus is basically, it’s fantastic for things
like food and water. You want food and water
to go down the esophagus because it’s going to
lead to the stomach. So you want food and
water to go that way, but you don’t want food and
water to go into the larynx. And so you want to make sure
that the epiglottis, that lid, is working really well. And if you’re swallowing
food and water, this epiglottis
will literally just kind of close up and
protect your larynx. But in this case,
that’s not happening. We’re not actually
food and water, we’re a little
molecule of oxygen, so let’s follow that molecule
a little bit further down. Let’s see what happens to it. I’m going to drag up
the canvas a little bit. Let’s make a little
bit of space, and I want to just
stop it right there because I want to show you that
the air molecule, the oxygen molecule has already kind of
made an interesting crossroads. It’s actually kind of broken
an important boundary, and that’s this
boundary right here. And on the top of this boundary,
I’ve included the larynx and of course, all
the other stuff we just talked about–
the mouth and the nose– and this is considered our
upper respiratory tract. So anything above
this dashed line is our upper respiratory
tract, and then, of course, you can then guess that
anything below the line must then be our lower
respiratory tract. So this is an important
boundary because people will talk about the
upper and lower tract, and I want to make sure you
know what is on which side. So on the top of it, is
the larynx and everything above that, and below
it is the trachea. Let me label that here. The trachea is right here,
the wind pipe or the trachea, and everything below that,
which, of course, mainly includes things like
the lungs, but as we’ll see a few other structures
that we’re going to name. So I’m going to
keep moving down, but now you know that
important boundary exists. So now let me just make
a little bit more space you can see the entire lungs. You can see the
molecule is going to go through the
trachea, and actually, I have my left lung
incompletely drawn. Let me just finish
it off right there. So we have our right
and left lung, right? These are the two
lungs, and our air is going to just kind
of slowly pass down– our molecule of oxygen
is going to pass down, and it’s going to go
either into the right lung or the left lung. Now here, I want to make sure
I just take a quick pause and show you the
naming structure. And the important
word of the day is the bronchi, which
alludes to one, or– sorry, I screwed it up
already– the bronchi, which alludes to more than
one– sorry about that– and bronchus, which
alludes to one. So bronchi means more than
one and bronchus means one. So just keep track of
these letters, I and U-S. So if we say that,
for example, we are going into this
area right here. Let me just choose a new
color so it’s really clear. This will be our main. If we go into this
spot– let’s say our air molecule or our oxygen
molecule goes this way– then we would say it’s in
our left main– I’m just going to underline as I
go– left main bronchus. That’s what we’d call that. And then if it went further,
let’s say it went down here, then instead of calling it
main, I would call it the lobar. That’s the word here. So I’d say it’s my
left lobar bronchus. And then if I wanted to
go a little bit further, I could say well now this
is my segmental, segmental. So these are the words that we
use, and this final one would be then my left
segmental bronchus. And of course, if we want
to talk about two of them, let’s say I want to talk about
both this guy and this guy, then I would say those are
my right segmental bronchi, because now I have to use the
top word because it’s plural. So that’s the naming structure. And another kind of
important naming structure you’ll sometimes see is primary
bronchus, secondary bronchus, and segmental, they
call tertiary bronchus. So you’ll see
either one of those, but I’m going to
stick to main, lobar, and segmental
because I think it’s a little bit easier and more
intuitive to remember it that way. Now, there are a couple of
important, interesting things happening already. So right here, this notch
or this point right here, this is our carina. This is our carina. So at the carina, you have
your break between the right and left main bronchus. And what I want to
point out to you is that this is a little
bit more vertical. This right-sided one is a
little bit more vertical, and the left-sided one is
a little bit more lateral. This is a little bit
more flat, or lateral. So it’s kind of a
cool thing to know, which is that if something was
to slide down the throat, let’s say a penny or a
peanut or something was to slide down here,
it’s more likely to go down this way simply
because of gravity. So gravity is going to push
things towards the right main bronchus more than
the left main bronchus because the right main bronchus
is a little bit more vertical. This is kind of a fun
fact that you now know. And actually, I guess I
didn’t do this already, but we should
actually take a break and make sure we name
some of these things. Remember this is called
our cardiac notch, and remember that’s one clue
to kind of telling apart the left and right lung. And the other clue we
said was the lobes, so of course, the right
one has the upper lobe, the middle lobe,
and the lower lobe, and the left lung only
has the upper and lower. So that’s an important clue. I just want to make sure we
don’t forget our little tricks that we’ve learned for
telling apart the lungs. So I’m going to take
a little pause there, and now, I’m going to show
you in a sped up version all of the different branch points. So for example, here we have
just a couple of branch points, one, two, and getting into
this segmental bronchi would be the third branch point. But I’m going to speed
things along and show you how many more branch
points there actually are before we get to the
final part of our lung where the gas exchange
actually happens, so enjoy. [MUSIC – NIKOLAI
RIMSKY-KORSAKOV, “FLIGHT OF THE BUMBLEBEE”] Going back to the very
point where we left off, we start with kind
of a bronchi, and we said that there is a
naming structure for how to name the bronchi,
but that’s really just the first three branches. And then after the
first three branches, all of the orange stuff,
all those branches going from branch point 4 all the way
down to about branch point 20, those are the
conducting bronchioles. So that’s the name we give them. They’re no longer bronchi,
they’re bronchioles. And so if you see that word
just keep that in mind, that we’re a little bit
further along in the lungs. And then after the
conducting bronchioles, you get into a few
more branch points, and we call them the
respiratory bronchioles. And actually the
final I should mention this the final
conducting bronchiole, sometimes you’ll see this
called the terminal bronchiole. It’s that kind of a bad
name because terminal sounds like we’re done,
but actually we’re just done with the
conducting bronchioles, and we’re still
kind of going into the respiratory bronchioles. I guess if I’m
only point to one, I should just probably
make it singular. And then finally, we get
into the alveolar ducts and the alveolar
sac, which is kind of a few alveoli put together. And if it’s plural as
alveoli, then singular just talking about one little part
of that sac would be alveolus. So that’s where our little
molecule of oxygen ends up, and this is kind
of where it ends up before it’s going to
participate in gas exchange. Now, this entire area, going
from respiratory bronchioles on downwards, this is all
called the respiratory zone, and anything above that is
considered the conducting zone, so anything above that. And that really includes not
just the connecting bronchioles, but conducting bronchioles, and
then all the stuff above it. So all the bronchi and even
the larynx and the mouth and the throat,
that’s all considered part of the conducting zone. So basically, oxygen
is going to come in through the entire conducting
zone, everything we just talked about, and
it’s going to go down into the respiratory
zone, and finally our little molecule
of oxygen is going to be very happy to
finally have made it to the very end of
the bronchial tree and is ready for
gas exchange now.