Under Part 2 here then.
Let's talk about
And again, I will say and I
will repeat over and over again,
it is not just the
lining of blood vessels.
It's actually a very
important cell type
that regulates a lot of
things in the circulation.
Back to our artery and vein,
so we have endothelium centrally
associated with the intima.
It lines the blood vessels,
we have to have an intact endothelium
otherwise, we will have problems
with thrombosis and blood clots.
Okay, so what does the
endothelium do and again,
all the little details
on the right hand side,
don't get too bogged down.
If you want to see
what that is all about.
There is a separate talk
on coagulation that I did
in one other part of
the Lecturio lectures,
so don't sweat that too much.
The main take home here is
that bullet on the left.
Endothelium maintains blood in a fluid
state, so it regulates coagulation,
and it makes a number of factors
that makes that possible.
It makes a number of factors that
locally regulate smooth muscle tone,
we've talked about
that regulates smooth
muscle tone in the arteries,
relaxed or contracted.
But there are things that are
made locally by endothelial cells
that also affect the underlying
smooth muscle cells of the media.
So nitric oxide and
prostaglandin I2 or prostacyclin,
that's the other name
for it are vasorelaxants.
include angiotensin II
that is made as a result of the
endothelium acting on angiotensin,
to make the the final
peptide that's active.
They are going to be
involved with platelets
that are going to be
making thromboxane A2
and superoxide anion, the O2-
is also going to be a very
As already indicated,
endothelial cells are important for
metabolizing a variety of hormones.
So again, all the details on the right
hand side we'll cover in a separate talk,
don't get too
bogged down on this,
except to see that
that has been acted on by
renin released by the kidney,
when it says, "We don't have
enough blood pressure dudes,
we need to increase
our blood pressure".
Renin acts on that precursor
angiotensinogen to angiotensin I.
And then there's a converting
enzyme made by endothelial cells,
that converts that to
the active ingredient,
the angiotensin II that acts on a
receptor to cause vasoconstriction.
Endothelial cells are really
important for regulating inflammation.
At those postcapillary venules,
the endothelium interacts
such as lymphocytes, and monocytes
to bring them into
sites of inflammation.
So it is a very delicate
dance that is performed
between the inflammatory
cells and the endothelium.
This is just showing you
more of that schematic.
Again, this was a separate talk in
other places in the Lecturio lexicon,
so you can look this
up in greater detail.
But basically leukocytes
are coming along.
And they don't just kind of happen
to glom onto endothelial cells.
There are in fact a number of molecules,
such as E-selectin and P-selectin
that bind to glycoproteins on the
inflammatory cells that allow them to roll
and then the endothelial
cells make integrin ligands.
They're going to be the
integrin super family of ligands
such as intercellular
that will allow the
binding to integrins
that have been activated on the
surface of the inflammatory cells.
And you see that
And then, within the inflammatory
cells crawl across the endothelium
that involves a interaction with
various molecules such as PECAM,
cell adhesion molecule,
otherwise known as CD31.
At CD31 on the endothelial
cells interacts with CD31
on the inflammatory cells
allowing them to crawl across.
So you can see inflammatory cell
recruitment very definitely.
An integrally involves the interaction
of endothelial cells and inflammation.
Endothelial cells have to transport
fluids, metabolites and larger molecules.
On the right hand side,
you can see that from left to right,
you can see that there's diffusion,
there's paracellular transport,
there's carrier-mediated transport,
there's receptor-mediated transcytosis,
there's absorptive transcytosis,
there is active efflux.
So there are a variety of ways that things
can get from one side of the endothelium,
which is where the fluid is where
all those metabolites are back out.
And conversely, things that are
being synthesized or metabolized,
or waste products in
the extravascular space
have to be transported back out into the
circulation to be taken someplace else.
What's being shown here is actually
the interaction between endothelium
and astrocytes within
the blood brain barrier,
which is a relatively
And yet, we have to transport
a whole bunch of stuff.
So at the brain can function that's a
very highly metabolically active tissue.
And as we already talked about,
endothelial cells will also
influence smooth muscle cell growth,
and in fact,
it's a major mediator.
Endothelial cells, major mediator of the
process that's going to be atherosclerosis.
there are lots and lots of details,
I refer you to another talk
that I've done elsewhere,
talking about how
Endothelial cells are the
source of new endothelial cells.
So if we've had damage and we
have to have neovascularization,
angiogenesis that has to come
from existing endothelial cells,
so they have to be able to
be kicked into the cell cycle
and have to grow, proliferate,
migrate and formed new tubes.
So these guys are really much
more than just lining cells.
I think I've beaten that
course very effectively.