About this video
The video uses a diseased artery with atheromatous plaque to show how blood can still move through a narrowed channel. Pressure readings along the vessel show a drop from about 90 to 70 at the narrowing, then a rise to about 80 downstream. Bernoulli's equation explains this: blood speeds up through the narrow point, so its kinetic energy rises and its pressure falls, while total energy stays the same.
You'll be able to
- describe the three terms in Bernoulli's equation: pressure energy, kinetic energy and potential energy.
- explain why pressure can drop where a vessel narrows.
- predict how velocity changes when blood moves through a narrower channel.
Key words
- Atheromatous plaque
- Fatty material and cell debris that builds up inside an artery and narrows its channel.
- Bernoulli's equation
- A relationship stating that the sum of pressure, kinetic and potential energy per unit volume stays constant along a flow.
- Kinetic energy
- The energy of movement, depending on fluid density and velocity squared.
- Density
- The mass per unit volume of a fluid, here the density of blood.
- Velocity
- How fast the blood is moving through a section of vessel.
Transcript
OK, so we left off talking about arteriolosclerosis, and specifically hyaline arteriolosclerosis, which is where you see pink, glassy material in the tunica media. And we talked about the two major ways or diseases where you see it getting there. So there's another term now I want to introduce, and that's called hyperplastic arteriolosclerosis.
It's kind of a mouthful. And here I think of it as what would happen if the process of hyaline arteriolosclerosis kept going. What would happen? So just keep imagining this vessel. And let's say that the situation continues. And now you've got years and years of protein buildup in that space, in the tunica media space.
Well what would happen next? Well you can start by imagining the same vessel, like that. This is the external layer, the tunica externa. And then right on the inside of that is the tunica media. And this tunica media, we know-- I drew a little bulge there by accident-- but we know this tunica media is full of smooth muscle cells.
And when these smooth muscle cells are around protein-- and they're not supposed to be around serum proteins, right? When they're around protein for a long time and they keep getting exposed to it, they react. And what they do when they react is they start multiplying.
So you get more and more of these smooth muscle cells. More and more of them. In fact, so many of them that it completely fills up the space. So the smooth muscle cells keep dominating all the space. Right? And they keep crowding out all the other layers. So in response to the proteins-- I haven't even drawn in the proteins yet, but let me show you some proteins that made their way into this space.
In response to these proteins, these serum proteins that went across the basement membrane, either because they got pushed out because of hypertension or maybe they got there because the base membrane became leaky. Either way, these proteins are now here. And the smooth muscle cells start dividing over time.
They start dividing a lot. And as a result, what happens is that you get kind of this inner layer of-- this is now the basement membrane and let me show that here. And this basement membrane has on the other side of it the endothelial cells. So we've got the same layers as before.
But the main difference, the main thing I want you to see, is that the tunica media is thick. It is thick. And it's thick specifically because of all of the smooth muscle cells dividing. Now I've drawn in the endothelial cells and I've drawn in a little, tiny lumen, a small lumen.
Now compare that to what it used to look like-- enormous lumen now has become very tiny. And so because it's so tiny it makes it really hard for blood flow through there. And under a microscope the way that people describe this if they see this is they say, well this looks like an onion.
So they call this onion skinning. And meaning that the onion has many layers to it. Right? And this actually looks like the many, many layers of an onion. That proliferated smooth muscle layer, the tunica media, is now very thick. And that's why it gets that name, the thick tunica media.
And the other issue is that usually you see this in cases of high blood pressure. So we talked about the fact that if your process of hypertension goes on a long time or if diabetes goes on a long time you might get this. The classic situation where you see this is malignant hypertension.
That's usually the one where you'll hear about this the most. And malignant hypertension, just to remind you, is when you have a rapid rise in blood pressure. And it can go as high as, let's say, 240 over 120, so really, really high. And usually these people have symptoms.
So generally speaking, people with the malignant hypertension have some sort of symptoms. So-- oh, extra hump on my m. So if you have malignant hypertension and you look in the blood vessels of these folks, there is a good chance you might see a very thick tunica media.
And we would call that hyperplastic arteriolosclerosis.
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