I'm actually just going
to take a step back, clear out some of this stuff. You've understood
the first half of how this process of
atherosclerosis happens. And we're going to finish
off the second half. So all of the action
is still going to happen in the tunica intima. So that much is going
to stay the same. And so far, we talked
about macrophages. And we talked about how
they form foam cells and they eat up all
the fat and they form this kind of lake of fat.
And so let me leave it there. So that's where the
picture's at so far. And now let's talk about
what happens after that. So the next step,
step five, basically what happens is the
smooth muscle cells– smooth muscle cells, we
haven't talked about them so far– they shimmy,
or they dance over. Let's write dance
over to tunica intima. So really, again, everything is
happening in the tunica intima, right? You can see that. That's where all the action is. And so when I say
they dance over, I'm being a little bit silly.
But basically, what happens
is that these cells, these red, smooth muscle cells–
these are the smooth muscle cells– they are going
to start migrating. They're going to start
migrating or moving. And they're going to start
migrating into this space. Maybe that one
will go over there. Maybe this one will go over
here, perhaps this one. And the way they
start migrating is that there's a lot
of action going on. The macrophages are there. They've got the LDL
in that lake of fat. And a lot of chemicals are
being released by these cells. And so they sense that
something's happening. So they kind of move over there. And what they begin to
do is make a fibrous cap. That's step six. So they make a fibrous cap. Actually, let me write who
makes it, so it's very clear. Smooth muscle cells,
S-M-C, smooth muscle cells make a fibrous cap. And what a fibrous
cap is is think about when you
were really young. And you were playing. And you didn't really pay
attention and fell a lot. You might have come
home with skinned knees.
And I certainly did. And my mom used to
always remark on that. And those skinned knees
turn into scabs, right? And so these smooth muscle
cells, these fibrous caps, basically think of
it as a scab, a scab that forms over
this lake of fat. So I've been drawing for
you this yellow lake of fat. And now these
smooth muscle cells, they come in and
say, well, we've got to make a cap
over this thing. Let me erase again and draw for
you what that might look like. So let's say that this
lake is getting bigger. This lake, over time, has
gotten really quite big. And you've got more fat in
here from all that LDL that keeps depositing,
because, going backwards, the endothelial cells
are not working well. And so you've got
this kind of weird set of endothelium
kind of around it. And the smooth muscle
cells come over, and they decide they're going to
help with making a fibrous cap.
So let me do that
in a new color. Let's do it in red. I guess that would
come up nicely. So they basically
make this cap here. And this cap mixes in to this
layer and settles in right there, right? And you've got some
endothelium over it, but sometimes you don't. And so this layer of endothelium
is pretty well disrupted, I would say. You've got this nice,
thick fibrous cap. And what's in that cap is things
like collagen, or elastin. So proteins are in this cap. So you've got a fibrous cap. And it's made of
collagen and elastin. So these are the
proteins that we know help with keeping all of
the cells in our body in place.
And so you can always point
to your bones, or your nose, and you can find
these proteins there. So it makes this fibrous cap. And so now, really, what
you have is fat with a cap. So that's kind of
how I think of this. This is fat with a cap. And it sounds simple. And in a way, that's a very
reasonable way to think of it. You've got the lake of fat. And over it, you've
got this fibrous cap. And what that does
is two things. You've already seen
that this is kind of starting to bulge into
the blood vessel, right? I'm going to go to that little
diagram in the corner again.
So you had a beautiful
blood vessel, nice and kind of circular. And then, now,
you've got this fat that's sitting in here,
this giant lake, right? And over it, I put a cap. So now you've got a cap here. So what has happened
to this blood vessel? Well, you had a certain
radius on that blood vessel. And that radius
has gotten smaller. So in terms of big key
ideas, key changes, your blood vessel has
actually gotten smaller. So one is smaller radius. And you can see that
in the picture, right? Smaller radius. And we know that radius
is related to resistance. So that means
increased resistance. Increased resistance
here to blood flow. And of course, I'm talking
about the distance from here over to here is smaller, now
that you've got something pooching out into the lumen. And the other change–
and this is actually quite interesting– is
that the wall itself is actually tougher. It's more stiff. And so right here, one
of the other things– actually, I didn't
talk about it much, but maybe I should say very
quickly right now– maybe even a step seven is that the smooth
muscle cells make– or let's say here– lay down calcium.
So when I say lay down,
what does that mean exactly? Are they like bricklayers? But when I say lay down
calcium, what I mean is that these cells
are actually going to start pretending in a way
that they are making bone. And actually, the
dead foam cells create this little
micro-environment where these smooth muscles start
thinking, oh, my gosh, maybe I should lay down some calcium,
put some calcium here. So they'll put a little
calcium nugget right here. I'll put another calcium
nugget right there. And I'll put another calcium
nugget there and there. And all of a sudden,
if you start looking, you start thinking,
oh, wow, this is actually very calcified. And this is actually looking
a little bit like bone. This is what happens with bone.
So they start calcifying
this entire area. And if you calcify this area,
if you start putting down these little
crystals of calcium, then what's going to happen is
that your arteries literally become crispy, crunchy, which
sounds kind of disgusting. I guess it is. But they're
essentially more stiff. And that's really
the key point, is that you get more stiffness,
or lower compliance. And that goes back to the
crunchiness of the vessel, or the inability to
be kind of flexible.
So lower compliance,
less flexible. Just as a little reminder
of what that means. So those are the big
changes that you see. And the lower radius
increases resistance. And the lower compliance
means that it's harder for these large
and middle-sized arteries to expand like a balloon every
time the blood pulses through. So both those things are
going to cause increase in your blood pressure..
