Lipid and protein transport in the lymphatic system Video Lecture - Class 12

We've already talked
about two purposes
of the lymphatic system.
The first was to bring the
fluid that was squeezed out
of the capillaries
back into the blood,
and the second was to help
out the immune system.
But there's one more.
There's a third.
And that's what we're going
to talk about in this video.
So let's look at a piece
of the small intestine.
Now, obviously the small
intestine carries bits of food
that your body wants to
absorb and use for energy.
So one of the most important
elements of that food
is little glucose
molecules, which
are absorbed and are used as
the primary source of energy
for the body.
So actually, since
it'll be helpful for us,
let's at least make
this two dimensional.
So let's look at some cells
here of the small intestine.
So these are cells lining
the small intestine.
And the way that glucose is
actually absorbed by your body
is that it's pumped
into these cells
here, in the cells
lining the intestine.
And then it's
pumped out of them.
And then once it's
here in this space,
it's able to diffuse into
capillaries which are nearby.
So it'll diffuse
into the capillaries,
and once it's there can go and
spread out over the whole body
and feed various cells.
But glucose is
not the only thing
which needs to be absorbed
in your small intestine,
and actually another
compound is fat.
So fatty acids which
are floating around
in your small intestine
need to be absorbed as well.
And the structure of these
things, to remind you,
looks something like this.
You've got this
carboxylic acid group
attached to a long
chain of carbons.
Now, like glucose,
these guys are taken up
by these cells in the intestine.
But when they're put
out by those cells,
they no longer look like this.
By the time they're
put out, they're
packaged into these actually
rather large spherical objects
which have a weird name.
It's chylomicron.
So they're packaged into
these spherical things called
chylomicrons, and
these chylomicrons
are useful for holding a
lot of these fats together.
But they have a
problem, which is
that chylomicrons,
as you might guess,
are too big to diffuse
into the capillaries.
So they can't do that.
But you don't want to
have chylomicrons just
accumulating here
in your intestine.
You want to spread them out to
the body where they're needed,
and so that's where our good
friend the lymphatic system
comes in.
So we have these
lymphatic vessels nearby
that are much easier to
enter than the capillaries,
and the chylomicrons able to
diffuse into these vessels
and be transported through
the lymphatic system
and eventually emptied
into the blood circulation
so that they can spread
throughout the body.
Because this is such
an important processes,
these lymphatic vessels
in your small intestine
are given a special name.
And that name is lacteal.
So the lymphatic vessels
in your small intestine
are known as lacteals,
and those are
the ones that take up your fats
in the form of chylomicrons.
So here we have our
third important function
of the lymphatic system, which
is to transport things which
didn't originally
come from the blood,
to transport them
into the blood.
And we can sort of
generalize it a little bit
and say that maybe a
little further away
from the small intestine
somewhere else you
have some cells that
are hanging out.
And actually, there
are some other things
which your body might want to
put into lymphatic circulation.
So you may have some
cells here or elsewhere
in the body that are
producing maybe some proteins
like hormones or maybe
some waste products.
And in some cases
those proteins might
have trouble getting
into the capillaries,
and these waste products
also might have trouble.
But you want these things
to get into the blood
because, for example,
for hormones, you
want them to be able to
travel throughout the body
and have their
effects on the tissues
that they're supposed to effect.
And for waste
products, you want them
to be able to get into
the blood and eventually
get to the liver where
they might be broken down
or to the kidney where
they can be excreted.
So in those cases, you
have this secondary system
of getting these things
into blood circulation
through the lymphatic vessels.
So these are
proteins and wastes.
And the reason
that we're talking
about these at the same
time as chylomicrons
is because these are all
things that don't actually
come from the blood, but we
want to put them in the blood.
And we can't do it
directly, so we put them
into lymphatic
circulation first.
So, now that we've learned
about the third purpose
of the lymphatic system,
it might be a good time
to review all three
purposes at once.
So why don't you pause
the video and see
if you can remind
yourself of all three.
Otherwise, I'll go ahead
and describe them here.
So the first purpose of
the lymphatic system--
let's draw another
lymphatic vessel here.
The first purpose was to
collect all the fluid which
was forced out of
the capillaries
by the high pressure that's
present in the blood,
to gather all that
fluid and bring it back
into blood circulation
via the lymphatic vessels
so that you don't have too
much fluid accumulating here
in the tissue.
So that's the first purpose.
This is just fluid with maybe
some small plasma proteins,
but not with any red blood
cells or anything like that.
The second purpose had to
do mostly with infection.
So if you have some
bacteria infecting
some tissue in your body, the
lymphatic system basically
offers a way to
bring those bacteria
to the attention of
your immune system.
And they do that by basically
taking them up and bringing
them to the nearest lymph node.
So that's a lymph node, and
that is where your B cells and T
cells are hanging out.
So that's the second
purpose right there,
the second purpose of
your lymphatic system.
And the third
purpose, of course,
is what we discussed today.
It's transporting other
things, such as chylomicrons
or other proteins or
wastes, transporting them
into the blood when they
have trouble simply getting
into capillaries the normal way.