- [Instructor] When you go to the doctors
for a routine checkup,
they usually start by feeling your neck
or sometimes behind of your ears.
Why do they do that?
What are they checking for?
And you may have heard of this
disease called elephantiasis,
where the limbs of the body
like, say, one of the
legs starts swelling up.
What causes this swelling?
To answer these questions, we need to look
at the lymphatic system of our body.
So what is this lymph?
Let's find out.
To figure out what lymph is,
let's start with something
that we already know,
the circulatory system.
It consists of your heart,
which doesn't look like this.
I'm pretty sure you know about this.
But since we are not
focusing on the heart,
let's just keep it this way.
Anyways, this heart pumps
this oxygen-rich blood
through this artery all the
way into the blood capillaries.
This is where the cells of our body
starts removing the oxygen from the blood
and starts throwing carbon
dioxide back into the blood.
And now the blood is deoxygenated
because it no longer has oxygen,
it has a lot of carbon dioxide.
And that's why it's shown in blue.
It goes all the way up through
this vein into the heart.
And then from there, goes
to purify in the lungs,
and then it gets purified,
comes back to the heart,
and the cycle repeats.
That's something we
have seen before, right?
But now let's talk about something
that we haven't seen before.
The first thing is remember that the blood
inside the arteries,
the vessels that take the
blood away from the heart,
so this one and this one.
They are under pressure, right?
Because as the heart squeezes,
the blood is under pressure,
which means the blood is pushing
on the walls of these arteries.
And another thing to focus on
is that if you were to zoom
into these capillaries,
so if you were to look at
one of those capillaries,
then we see that the
walls of the capillaries
have holes in them.
So now think about it.
The blood over here is under pressure,
that means the blood is
pushing on the walls,
and the capillary of that walls,
and the wall of that
capillary has holes in them.
What's going to happen?
Well, if you thought
that due to the pressure
the blood starts oozing
out of these holes,
then you are absolutely right.
Now we will not call this blood
because blood contains plasma,
which contains proteins
and then it has RBCs,
and WBCs and everything, right?
Now what oozes out is just the plasma.
RBCs can't ooze out because
the holes are too small
for RBCs to go out.
So RBCs don't ooze out.
The plasma comes out with
a little bit of proteins.
So some small proteins, not big ones,
but some small proteins also ooze out
along with this plasma.
Let me just clean this up a little bit.
Okay, so this plasma that oozes out
and then fills up this
space between the cells,
this is what we call the lymph.
All right?
And it's pronounced as lymph,
with an F over there.
So how is lymph different than blood?
Well, lymph does not
have RBC in it, right?
And as it is our lymph,
it's pretty much colorless.
In fact, the word lymph
comes from the Latin
which means water like, water like.
And why is it called water like?
Because it is pretty much colorless.
And this means wherever these
capillaries are present,
the plasma will ooze
out to form the lymph.
And capillaries are
found all over our body.
So you will find this lymph
pretty much everywhere
inside your body.
Okay, so what's the big deal?
Why should we care too much about this?
Well, first of all, this means
that every time blood goes
through the capillaries,
it will start losing some of its plasma.
That's bad because that means the blood
will start getting thicker and thicker
because it starts losing plasma.
And eventually, it becomes
more and more difficult
to circulate it because it's so thick.
And that means our cells
will not get any oxygen.
And I'm pretty sure you
know what would that mean.
The cells would start dying.
Secondly, as this lymph
starts getting accumulated
within our tissues, it
starts pushing on the cells.
And the tissues will
start getting puffed up.
And that causes swellings.
And that means our organs
will start swelling up.
And that's one of the reasons why
in elephantiasis our limbs swell up.
This is because of the accumulation
of the lymph over there.
Now before we talk about
how our bodies tackle this,
I'll tell you what I
should think about this.
I should think that this
is such a bad design.
If we don't want the plasma to leak out,
then why are there holes
present in the capillaries?
What a bad design, right?
Well, guess what?
The holes are necessary.
Because, you see, cells
aren't only exchanging gases
like carbon dioxide and oxygen,
which can easily pass through the walls
but they're also exchanging
other stuff like nutrients.
For example, glucose.
Also the cells need glucose.
They get that from the blood itself.
Then the cells produce
some waste products,
like some nitrogen as waste sometimes,
and that needs to be
put back into the blood.
And for that, we need space.
They can't go through the wall
as they are big, big molecules.
They can only go through the holes.
And so capillaries need that
holes to exchange the stuff.
And so since holes are
absolutely necessary,
there's nothing we can do
about this plasma leaking out.
And so the big question
is what does your body do about this?
Well, thankfully, your body
has a separate set of vessels,
which are called lymph vessels,
which clear out this
lymph from your tissues.
So just like how we have blood vessels
and blood capillaries, these
are called lymph vessels.
So the thick ones are called lymph vessels
and the thin ones are
called lymph capillaries.
So over here if I were to show
you those lymph capillaries,
this lymph fluid enters
into these capillaries
and it clears the lymph
out from your tissues.
Now one difference
between blood capillaries
and lymph capillaries
you can immediately see
is that blood capillaries
connect two blood vessels, right?
They're open-ended.
But as you can see, the lymph capillaries,
they are closed at one end.
Can you see that?
They're closed.
And so I was really curious
when I was studying this.
How does the lymph just enter
into this lymph capillary?
It's pretty awesome.
Let me show you how.
Let me get rid of this leg.
And let me zoom in to
one of those capillaries.
The cells of this lymph
capillaries, as you can see,
have little bit of overlapping structures.
That's very important.
So now when they are
surrounded by these lymph fluid
in the tissue, it's the
same lymph fluid over here,
the fluid starts pressing on the walls.
So it starts pressing on the walls.
And now look carefully what happens
when the fluid starts
pressing on the walls.
These walls open up.
Look at the junction carefully.
The walls open up like this.
Cool, right? Let me
show you one more time.
The walls open up like this.
And now the fluid enters the capillary.
And now if you're wondering
why doesn't the fluid
just flow back out
through the same opening,
then once the fluid gets inside,
it'll start pushing from inside, right?
And as it pushes from inside,
look at what happens to these walls,
they will start closing now.
Look carefully.
They will now close.
So it's like a one way door.
It only allows the fluid in
but doesn't allow it to go out.
That's how these capillaries
clear out the lymph from your tissues.
So now the next question would
be where do these vessels
take that fluid eventually?
Where do they put it?
Can you guess this?
Can you guess where
they should put it back?
Well, since lymph is basically plasma
leaking out from the blood,
it makes sense to put it back
into the bloodstream, right?
And so these lymph
vessels eventually connect
to one of the blood vessels
to recycle it back into
our circulatory system.
But a question for you would be
do you think we should
connect these lymph vessels
to an artery?
Or a vein?
Can you pause the video
and think about which one
would you connect it to?
All right, let's see.
If we were to connect this to an artery,
then we would have hard time
trying to force that lymph
into the circulatory system,
because the arteries, inside the artery
the blood is under a very
heavy pressure, right?
In fact, the pressure of the blood
would actually force the lymph out,
back out of these capillaries.
It might even shatter the
walls of the lymph capillaries.
This is gonna be very bad.
So we want to reenter it somewhere
where the pressure is very low.
And that is somewhere in the veins.
And so the lymph vessels
eventually connect
to a vein, somewhere close to the heart,
that's where the pressure is the lowest,
and then it reenters into
our circulatory system.
And this is how the lymph vessels ensure
that we get back the lost
blood from the capillaries.
And so let's write this down.
One of the most important
jobs of the lymph vessels
is to clear that lymph out.
So I'm just going to write clear lymph.
So it takes the lymphs from the tissues
and puts it back into the veins.
And so we are done, right?
Because your blood is regaining
the lost plasma from
the capillaries, right?
Well, not yet.
Not quite.
And the reason is what if
your vessels, lymph vessels,
start picking up something unwanted.
Like, say, for example, your tissues
are infected by some
pathogens like some bacteria.
Then when the lymph
enters into these vessels,
even the bacteria might
start entering over there.
And then these bacteria might
enter into your bloodstream.
You don't want any bacteria
in your circulatory system.
That's gonna be pretty bad.
So what to do?
Don't worry, your lymph
vessels are awesome.
They have security points all over them.
These are called lymph nodes.
Let me just write that down.
Lymph nodes.
And they have a lot of WBCs over there.
WBCs are like police.
So when the lymph enters into these nodes,
if there are any unwanted
stuff like bacteria,
the WBCs are going to kill it.
This will make sure that no unwanted stuff
enters your bloodstream.
It's pretty cool, right?
And so you see these lymph vessels
also help in killing unwanted
stuff from your body.
So they also help in immunity.
So they help in immunity.
That's pretty cool.
And guess what?
If any of your lymph vessels
pick up a lot of bacteria,
then a lot of the WBCs will
gather in that lymph node
and that node will now swell.
Which means swollen nodes
are an early indication of infections.
And that's what the
doctors are checking for
when they are feeling your neck.
It turns out there are lot of these nodes
near your neck and your ears.
And so they touch that and see
if any of those are swollen.
If they're swollen,
good chance there's an
infection somewhere.
Now before we wind up,
another important job
that the lymph vessels have
is to transport fat into your bloodstream.
So I'm just going to write
transport fat, for short,
into your bloodstream.
And what I mean by this
is imagine you have your small intestine
somewhere over here.
All your food gets digested
and then they come over
the small intestine.
And most of the nutrients
can directly enter
into the capillaries through these holes.
And that's how the nutrients
enter your bloodstream.
And then they are
circulated to all the cells.
But the digested fats, which
come out of your intestine,
are just too big to enter
into these capillaries.
So they can't directly
enter the bloodstream.
So they are again picked
up by the lymph vessels
or the lymph capillaries,
then they go through the lymphatic system
and then they reach the bloodstream.
And so that's how the fat
enters your bloodstream,
through the lymphatic system.
So what did we learn in this video?
We talked about the awesome
lymphatic system of our body,
which consists of the
lymph, the lymph nodes,
and the lymph vessels.
The lymph is basically the plasma
that leaks out of your
capillaries due to blood pressure.
This lymph is picked up
by these lymph vessels,
which recycle it back into
our circulatory system
through the veins.
And the lymph nodes act like security
to make sure that no pathogens
enter our bloodstream.
And finally, the lymph vessels
found near the small intestine
help in transporting these digested fat
into our bloodstream as well.
