Hello, bio people. Today we're going to be
moving on to the topics of ventilation
in both humans and goldfish. Before we
dive in to deeply, I want to make sure
we're all on the same page; that we all
know that respiration and ventilation
are not the same thing.
Respiration is the physical gas exchange
in and out of the cell where oxygen
ultimately becomes co2 through cellular
respiration. So, almost all cells in your
body are undergoing restoration right
now.
Ventilation is the movement of air in
and out of an organism, so when you take
a deep breath and pull air in and then
exhale and expel the air that's
ventilation not respiration. A good way to
remember this is that a ventilator is a
machine that they tend to use on
patients who can't breathe on their own.
It physically pushes air in and out of
their lungs, so if you hear a reference
to somebody who is being kept alive by
machines or if they're thinking about
pulling the plug on someone
this is usually what they're referring
to. To start off, we're going to look at
the set of mammalian lungs. While some
creatures have slightly different setups,
for instance whales have a trachea that
exits out of the top of their head, the
overall layout is pretty much the same.
Oxygen first enters through an area
called the trachea, also known as the
windpipe. You can feel your own if you
look up at the ceiling and then rub the
area of your neck just under your chin.
The oxygen-rich air then flows through
the area called the bronchi. Each lung
has one bronchus that connects it to the
trachea. It then flows through smaller
tubes called bronchioles, the air
terminates in parts of the lungs called
the alveoli. Alveoli are made up of a
series of very small bubbles with lots
and lots of blood vessels surrounding
them. Each alveolus has a huge amount of
surface area and lots of blood vessels
surrounding it where oxygen can diffuse
into the blood and carbon dioxide can
diffuse out. The carbon dioxide that used
to be dissolved in the blood is now
inside the alveolar air sac where it can
be blown up the bronchioles, out the
bronchi, and then out of the trachea and
eventually out of the animals mouth, nose
or blowhole.
All right, now we're going to move on to
goldfish ventilation and we're going to
see how that's different from human
ventilation. When the fish's mouth is
open, the operculum slits are flush
against the sides of the fish's body,
meaning that the operculuae are closed. In
fish, water flows through the mouth into
the buccal cavity and then over the
gills and out underneath a flap called the
operculum. This flap right here is the
operculum; it's a protective covering
that covers the gills to prevent damage.
You can tell if a fish is ventilating by
the fact that it's operculum is
flapping. We're now going to slice our
fish open this way in order to look at
what happens inside its body when it
ventilates. Right now, what we're looking at is
a cross-section of the fish where the
plane is parallel to the floor. On the
left side of the screen you can see its
mouth and then on the top and bottom of
your screen you can see its operculum.
It has an operculum on both sides of its
body; one on the left and one on the
right, which protects the gill slits
which are right here. When the fish opens
its mouth, water flows into the area
called the buccal cavity. The fish needs
to push the water over its gills and
then out of the operculum in order to
extract the oxygen and remove the carbon
dioxide from its tissues. To do this, the
fish first closes its mouth. When it does
this, the water is pushed out of the
operculum openings over the gills and
back into the water. As the water moves
over the gills on its way out of the
operculum, the oxygen is extracted and
moved into the fish's blood stream and
carbon dioxide is removed. We'll take a
closer look at this in one second. We're
now going to zoom in on these structures
here on either side of the fish which
are known collectively as the gills. In
this picture we can clearly see the
structures we call gills and we can also
see the fish's operculum opened right
here. Notice that there appeared to be
many layers of gills on this side of the
fish. This supportive structure right
here is called a gill arch and attached
to it are many fibers
that collectively extract the
gases from the water. The red structures
attached to the gill arches are called
gill filaments. If we look even more
closely at each gill filament, we will
notice that there are tiny hairs on them
called lamellae. The nature of the
lamellae makes the gill filaments a little bit
fluffy and greatly increases their
surface area just like the cluster of
bubbles in the alveoli of the lungs
increase the lung surface area. The more
surface area you have, the easier it is to do
gas exchange. We're now going to look
even more closely at the lamellae in
order to see how gas exchange occurs in
fish. In order to understand how lamellae work, we
need to understand the concept called
counter-current exchange. Here I've drawn
two sections; one that represents the
water and one that represents one of the
tiny hairs on the gill filaments called
the lamellae. Now notice that the membrane
of the lamellae is very very thin.
This means that there is going to be a
very short diffusion distance just like
there was in the lungs. The goal of the
lamellae is to get oxygen to diffuse out
of the water and into the fish. To do
this, we have the water flowing in a
different direction from the blood flow.
Inside the gills in order to keep the
fish alive, diffusion of the oxygen must
be occurring at all times; if it stops
the fish will suffocate. The blood that
initially enters the gills from the back
of the gills has relatively little
oxygen in it. For the sake of argument
let's say it has about sixty percent
oxygen. In order for the fish to survive
we need a hundred percent oxygen in its
blood,
otherwise the fish's tissues will not
get enough. The water that comes in
through the fish's mouth is full of
oxygen;
it's a hundred percent saturated. As it
moves farther through the fish, it's
going to lose oxygen which will diffuse
into the lamellae. The blood that comes
into the lamellae from the fish is going
to start off with very little oxygen but
will gradually pick up more and more as
it moves past the end of the gill
filaments. When the blood begins to return
to the rest of the fish,
it has a very high oxygen concentration.
The concentration of oxygen in the water
runs in reverse; when the water initially
entered the fish's mouth, it starts off
with a hundred percent saturation and
then gradually decreases as the oxygen
is sucked into the blood inside of the
fish. When it finally exits the fish, it's
going to have less oxygen than when it
began. Remember that things like to flow
down concentration gradients from areas
where there is more of it to areas where
there is less. Because there is always
more oxygen in the water compared to the
bloodstream, the oxygen is always going
to flow into the lamellaei rather than
flowing the other way. No matter whether
you're in this area of the lamellae or
whether you're in this area, the amount
of oxygen is always greater in the water
than it is inside the blood vessels.
Because of this, diffusion occurs
constantly rather than coming to a halt.
In order to really understand this, we're
actually going to flip them around and
see what would happen if we had con
current exchange when both the water and
the blood flow in the same
direction. Now let's look at what would
happen if both the water and the blood
flowing in the same direction. Again
since oxygen likes to diffuse down the
concentration gradient, it would flow
really nicely on this part of the blood
vessel right here where the
concentration gradient is very big.
However, it would slow down towards the
middle and end of the blood vessels
because the concentration gradient gets
a lot smaller.
Eventually it would come to a complete
stop when the concentration of oxygen in
the blood and in the water are the same.
When diffusion is no longer taking place,
it causes lack of oxygen to happen to
all of the fishes tissues and the fish
will die. So in order to make sure that
diffusion is constantly happening, we use
a counter-current exchange system where
the blood and the water flow in opposite
directions. One more key thing, surface
area is key in biology; the more surface
area you have easier is to do gas
exchange. This is why gills tend to be
very fluffy. That's it! Don't forget to subscribe!