So we've talked a lot
about the lymphatic system. And in this video, I
wanted to talk more about lymph, which is the fluid
that's in the lymphatic system. So we know that lymph comes
from blood vessels originally. It's the fluid that's kind of
squeezed out of blood vessels. And so here let's say
this is a capillary. I'm drawing the endothelial
cells around the capillary. So lymph is what comes out
of here, what's squeezed out through the little holes
between the capillaries. And just so we have our
terminology straight, really, lymph is only
called lymph once it gets into the lymphatic vessels. So once this fluid
get into here, now we can actually
call it lymph. But before it does, it's more
called extracellular fluid, because it's outside the
cells that are out here. But really, the
composition is the same. And so this is just
a semantics thing. So in this video,
let's try to figure out exactly what lymph is made of. And so to do that,
let's start with blood, because lymph originally
comes from there. So in blood, we obviously
have red blood cells. So let's draw a couple
of those in here. These are red blood cells. And in reality, we should
draw more than a couple, because we know that blood is
actually consisting of about 40 or maybe even 45% red
blood cells, 45% by volume. And that's in the
average person. If you're anemic, it'll be less. So blood has about 40%. We're drawing much
less than that here. But it's kind of hard to
draw them all packed in, so let's leave it like that. And so other than
that, of course we have water, which
we'll draw white. This is water. And we also have proteins. We have proteins. And we'll draw those
of varying sizes, because proteins
really do vary by size. And we have many different
kinds of proteins in the blood that do many
different kinds of things. And that's all that
we'll draw here. Even though there are also
glucose molecules and fats and other things in the blood,
we can ignore those for now. So what gets out here? What manages to squeeze through? Well, we know that
the red blood cells don't manage to squeeze through. So certainly, by the time we
get to extracellular fluid, we'll have 0% red blood cells. And so lymph will have
no red blood cells. But other than that, let
me ask you a question. Do you think that
lymph has more protein or less protein than blood? And let's just say
by concentration. So it's actually
a tough question, because if all the protein came
out freely of these vessels, then lymph would actually have a
higher concentration of protein than blood, because
blood had these red blood cells that were taking up space. And so the protein
was, so to speak, diluted by this huge
amount of red blood cells. And out here, it won't be
diluted by red blood cells. But actually, there's less
protein out here in the lymph. And that's because
water gets out so much more easily from
these capillaries than protein that you end up with
fairly dilute fluid here. So proteins have a kind
of tough time getting out. And certainly some
of them do get out. And so we'll draw those here. But it's much less
than are in blood. And so we end up
with about a half to a third the amount of protein
in lymph compared to blood. So lymph has about a half
to a third versus blood. Let's draw that like that. Another thing we
can ask ourselves is what kinds of proteins are
going to be in this lymph? Since we said that
there were so many different kinds of
proteins in the blood, which ones are going
to get into the lymph? And actually, it's going to be
the smaller ones, generally. The smaller ones are going to
have an easier time getting through these holes. And so we can say, for
example, that the ratio of a small protein like
albumin, over a large protein like an immunoglobulin-- and
I'm just going to write Ig. These are antibodies. And they're generally
bigger than albumin. So the ratio of albumin
to immunoglobulin is going to be bigger in lymph
than it will be in blood. And the reason for
that is what we just said, that smaller proteins have
an easier time getting through than large proteins. So even if you have less albumin
overall in lymph compared to blood, you'll have
a greater albumin over immunoglobulin ratio. And let's actually
pause here a moment before we move on from talking
about protein in the lymph, because it's actually very
important that there's less protein in the lymph
than there is in blood. Because if you watched
one of the earlier videos, you remember that we said that
actually the way that fluid gets squeezed out
of the capillaries is not so straightforward. Because what happens is, first,
some of it gets squeezed out. But then some of it
gets taken back up. And the reason why some
of it gets taken back up is because, as you travel
down the capillary, the hydrostatic pressure
that pushes this fluid out goes down. So there's less
pressure pushing it out. But there's still some
pressure pushing it out. So why is some of
this fluid going back into the blood vessel? And the reason is that
there's a higher concentration of things like proteins in here. And that higher concentration
makes the blood more-- and this is going to be a scary
word-- but more osmotically active. And so there's a higher osmotic
pressure pulling fluid back in, exactly because you have
more protein in the blood than you do out
here in the lymph. And so it's very
important that you do have more protein
in the blood. And now I'd like to ask
you a question, which is, how much lymph do you
think is produced per day? So the amount of
lymph that's produced is the amount
that's squeezed out of these blood vessels minus
the amount that's taken back up. And so how much do think that
adds up to in an entire day? So how much lymph do we produce? And let me give you
a moment to guess. So how many liters? So come up with a number,
the number of liters of lymph that we produce per day. And the answer is 3. So we make about 3
liters of lymph per day. And that's all filtered out
through these capillaries. That's a word people
like to use, filtered. And actually, it turns out
that the amount that actually comes out first is
about 20 liters. And I'm going to draw it
small because these are really small details that you
don't need to know. But about 20 liters
is squeezed out. And then about 17
liters comes back in. And so that leaves a
difference of about 3 liters that comes out per day. So this is per day. The final thing that we
should really mention is that lymph has a different
composition depending on where you are in the body. So let's quickly
look at a human body so we can talk about
how lymph might differ from place to place. So here is a human. And the one thing
we talked about was how, in the small
intestine over here, your lymphatic vessels, which
there are called lacteals, are taking up a lot of
fats, a lot of chylomicrons. And so as you might
guess, the composition of lymph coming
from there is going to be much higher in
those chylomicrons, which are collections of fats. So there you're going
to have more fats. Whereas, when you go
to the liver-- and this is not something necessarily
that you know or should know, but it's interesting fact. The liver produces
a ton of proteins that end up going
into your blood. And one of the ways that
they get them into the blood is to put them into lymph. And so your lymph
coming from the liver has a much higher
concentration of protein than your lymph
coming from elsewhere. And it actually can get to
as much as 10 times as much. You can have 10
times as much protein in the lymph coming from the
liver compared to other places. And so this number here that
we gave, one half to a third, is really just an average of all
the lymph all over your body, because the protein
content can vary widely from place to place. As we know, eventually
all the lymph vessels, including the lacteals coming
from your small intestine, they all join up. And they come up your body. And also the ones
coming from the liver will merge and join and come up
and travel up through the body. And eventually they'll be
put back into circulation. And that will be here
in the veins up here, which I'll draw in
blue, even though it's getting a little
confusing there. I'm drawing them in blue
because we generally draw veins in blue. And those merge and
go to the heart. So all these
different lymph fluids with different
compositions come together and go back into circulation.