hey y'all its Dr. Brown back here again. This time we're gonna be talking about
blood vessels, and specifically the walls of blood vessels. So although we have, you
know, both arteries and veins. Arteries come in various types. You have
elastic arteries, and you have muscular arteries, you have small arteries and
arterioles which are even smaller, and like veins you have little bitty venules
and larger veins. There are three fundamental layers that can be found in
the wall of a blood vessel, and it's modifications to those three layers that
impart function to those different types of blood vessels. So if you know what the
three layers are, and what goes into making them then you can recognize how
those layers are modified, and how those modifications will enable say an elastic
artery near the heart to function differently than for instance a venule
draining one of the peripheral tissues. So let's jump right in and look at these.
So we have a cartoon on the left and an actual micrograph on the right, and you
can see in the cartoon that the three main layers of an artery, in this case,
have been labeled, and, and while we're using an artery as our example that's
because these arteries have all the things that you could see, and all the
other things we're gonna look at the different types of arteries as well as
veins are gonna have some or all of these, but this has everything in it so
that's why we're using it as an example. So the innermost layer of a blood vessel
is referred to as the tunica intima; it's also sometimes called the tunica interna.
We'll see both of those depending on your textbook, and this is going to be
the one closest to the lumen. If we look at our micrograph over here the
lumen of any hollow thing is the hollow space in the middle of it, and the tunica
intima is going to be comprised of up to three different structures two of which
are labeled in our cartoon. So the endothelium is the layer of endothelial
cells, remember those are just epithelial cells that point inward, and these are
going to be closest to the lumen, so it's going to resemble a squamous epithelium,
a simple squamous epithelium very closely.
Underneath that, and not labeled in the cartoon, so we'll just have to label it
here, is a sub endothelial layer, and it's really just a basal lamina. So it's a
loose connective tissue. So you've got some areolar tissue under here. You can
see they've even...the people who drew this cartoon is a guy named Michael blah?
I think his first name is blouson. You can see the type one collagen fibers, and
the elastin fibers, and stuff that he's rendered in there. And then finally an
internal elastic membrane, or your textbook uses the term internal elastic
lamina. Remember lamina just means layer. So some blood vessels are gonna have all
three of these. They're going to be various thicknesses. Some of your simplest...
..blood vessels, the capillaries, just have an endothelium and the subendothelial
layer that's it. The middle layer of the blood vessel
here is called the tunica media, and it's primarily comprised of smooth muscle;
however, ...change my pen color down here...there can be, and especially in your
larger arteries closer to the heart where where there's a lot of force being
exerted on them, in between the layers of smooth muscle you can also find little
elastic lamina inside the tunica media. So the tunica media is always going to
have smooth muscle, but it can also contain these elastic lamina, these
layers of elastic tissue that help provide support to the tunica media. The
tunica media can but doesn't always end in an external elastic membrane. You see
these especially in the elastic arteries of the lungs. And then finally the
outermost layer is the tunica externa, also called the tunica adventitia, and
the tunica externa or tunica adventitia is largely connective tissue it's going
to help anchor the blood vessel in the tissues through which it's running, but
it can also contain, not shown in this picture,
little bitty arteries and veins of its own. So in some blood vessels these
tissues, in the tunica intima and tunica media, can
get blood and nutrients from the...sorry...can get oxygen and nutrients from the blood
flowing through the blood vessel, but in your larger blood vessels, larger
arteries or in your veins where this blood may not be accessible, or it may
not contain a lot of oxygen and nutrients. Then you got to have your own
blood supply to the outer portion of the blood vessel to supply oxygen and
nutrients to the more peripheral zones. And these blood vessels found in the
tunica externa are collectively referred to as the vasa vasorum, which i know is a
very harry potter sounding word, but it simply means the vessel of the vessels.
So it's the blood vessel for a blood vessel so let's look at these things
over here in the micrograph on the right. So we can see i've labeled the lumen
here, the tunica intima is here. So in between the two blue lines I just drew.
So you can see here the kind of darker colored border that's the internal
elastic lamina. So everything to the outside of the blue line I'm drawing is
tunica intima or tunica interna. The tunica media is gonna be all this
business here. So that's the tunica media, and you can
see the pink staining or red staining smooth muscle. You can see that there
are some elastic laminae in this particular artery. And then finally label
number six out here this is the Tunica externa or tunica
adventitia. So let's look at this on one more time on an unlabeled micrograph and
see if we can distinguish these layers. So let's switch back to the red pen I
think, that'll show up better against this purple. The lumen here you can
actually see these are the red blood cells. Here. Here. Those are all a bunch of
erythrocytes there. The Tunica intima, Tunica interna, runs from the internal
elastic lamina, which in this micrograph is stained dark purple, all the way out
to here. So that's the Tunica intima. The tunica
media goes from just underneath the internal elastic lamina to the external
elastic lamina. This is a lung artery; that's why it's got the
the external elastic lamina or external elastic membrane. And then finally, out
here we can see the Tunica externa or tunica adventitia. So Tunica interna here,
tunica media here, and then Tunica externa here. Hopefully that helps. You
can identify these three we're going to have some more opportunities to practice
throughout our module on circulatory systems, but that's it for now.
Study hard. See you later.