Atherosclerosis | Circulatory System and Disease | NCLEX-RN | Khan Academy

Aug 18, 2023

Atherosclerosis | Circulatory System and Disease | NCLEX-RN | Khan Academy

Created by Vishal Punwani.

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Content

1.831 -> - [Voiceover] We know that atherosclerosis

4.067 -> is the main contributor to coronary artery disease,

8.109 -> and in the coronary arteries, atherosclerosis

11.34 -> will cause build-up of these fatty

14.713 -> cholesterol-filled plaques, like so.

18.085 -> You can see me drawing them in here,

19.975 -> and they're occurring all over the coronary arteries

22.819 -> so what they do is they sort of obstruct

25.329 -> blood flow down the length of the coronary arteries

29.391 -> and through all the branches of the coronary arteries

31.85 -> because they're just these big bulges of fat

34.451 -> that are in the way.

36.157 -> So how do they develop?

37.641 -> What exactly is this process of atherosclerosis?

41.237 -> Well, let me show you what this looks like

43.167 -> in a snapshot before we actually

46.133 -> look at the mechanisms.

47.738 -> I'll take this piece of coronary artery here,

49.862 -> let's say this piece right there,

52.016 -> and we'll blow that up.

53.911 -> If we look at that ...

54.791 -> When it's nice and healthy, it's going to look like this.

58.67 -> Here's our healthy blood vessel.

60.742 -> Nothing built up inside.

62.347 -> You can see blood is going to flow through this way.

67.224 -> This here is a cross-section of the artery.

70.154 -> So as far as we can tell, blood can flow

73.913 -> smoothly and nicely through this blood vessel,

76.107 -> no obstruction, everything looks good,

78.464 -> but when you start getting atherosclerosis happening,

81.633 -> things can get a little bit different.

83.663 -> When you start getting atherosclerosis happening,

86.612 -> your coronary artery might start to look

88.705 -> something like this.

90.9 -> Immediately, we can see that there's a pretty big difference

95.228 -> between the first vessel here, the nice clean one,

98.762 -> and the second vessel here, the atherosclerotic,

102.914 -> sort of fatty plaque vessel here.

105.681 -> All of this yellow stuff is some gross fatty plaque

109.266 -> that's been deposited into the vessel wall.

111.668 -> If we look at the cross-section here,

113.518 -> we can see that it's really doing a number

117.5 -> on the amount of blood that's able

119.166 -> to flow through this vessel.

123.107 -> If we're blood here in red,

125.545 -> we can't actually get through this vessel

128.899 -> quite as much as we could through here.

130.929 -> Look how much room we had in this one.

134.042 -> Because of all this build-up,

135.197 -> this is why we're going to get downstream symptoms.

139.344 -> How, exactly, does this happen?

140.866 -> Well, let's redraw our own arteries

143.893 -> so we can go through it step by step.

147.123 -> Here's our blood vessel there.

149.136 -> Now I'm drawing the three layers

151.939 -> of the wall of the blood vessels.

154.539 -> On the very inside of the blood vessel,

156.612 -> as part of this pink layer here,

158.827 -> we have a single layer of cells called the endothelium.

163.093 -> Let me just draw out the endothelium here.

166.567 -> Although it's just a single layer of cells thick,

169.35 -> the endothelium has a lot of really important roles.

173.028 -> One of its really important jobs is to act as a barrier.

176.543 -> It acts as a barrier between stuff that's in the blood

179.814 -> and the rest of the blood vessel wall

183.065 -> so stuff can't just pass through

185.035 -> and get into the rest of the blood vessel wall.

187.758 -> This barrier function will become

189.081 -> pretty relevant in a minute.

190.603 -> You'll just have to take my word for it for now.

193.57 -> Another really important job that the endothelium has

196.395 -> is to secrete proteins onto its surface

200.458 -> that prevent clotting.

202.063 -> That keeps blood flowing nice and smoothly.

204.642 -> Those are two of its major jobs.

206.735 -> It has a couple more, but those are the ones

208.726 -> that are relevant in atherosclerosis.

211.489 -> All right, so you remember that big

212.912 -> fatty vessel from before?

214.496 -> Well, how do we get from this,

215.817 -> our nice clean blood vessel,

217.564 -> how do we get from this to that?

219.474 -> Let's take a look.

220.612 -> The first thing that has to happen

221.912 -> is that there has to be some irritant present,

224.675 -> something in the blood that's going to predispose

226.748 -> this atherosclerosis to happen.

229.368 -> So, what are some irritants?

230.75 -> Things like too many lipids,

232.884 -> so, specifically, fats and cholesterol,

235.505 -> LDL cholesterol, the bad cholesterol.

238.511 -> Let's actually put some of this cholesterol

240.32 -> in the blood vessel so we can see it really clearly.

243.529 -> I'll just label it LDL, LDL-C, actually,

246.72 -> so you know this is cholestero, LDL-C.

250.194 -> Another irritant, probably the worst one,

252.531 -> is toxins from cigarette smoking.

255.842 -> So we'll put some toxins in the blood

257.995 -> from cigarette smoking.

260.168 -> We'll do them in gray here.

261.529 -> Another major one is just hypertension,

264.7 -> high blood pressure.

265.959 -> We'll try to show that pathologically high

268.092 -> blood pressure here by these arrows.

270.266 -> High blood pressure.

271.607 -> This means high blood pressure.

274.248 -> I'll actually write hypertension here,

276.016 -> because I just want to make it clear

277.702 -> that it's the chronic exposure to high blood pressure,

281.481 -> it's not just high blood pressure every once-in-a-while.

284.915 -> That's our first step, to have an irritant present.

287.861 -> Our second step is to actually have damage

290.38 -> to the endothelium by the irritant.

294.342 -> So our barrier, now, is broken down.

296.861 -> It's started to break down.

298.73 -> That's step two.

299.707 -> That's actual damage of the endothelium.

302.592 -> In step three, regardless of whatever damaged

305.72 -> the endothelium, I mean, if it was toxins

307.937 -> or if it was the cholesterol

310.151 -> or if it was the high blood pressure,

311.879 -> regardless of what actually damaged the endothelium,

314.784 -> what happens next is that the cholesterol

316.694 -> will jump in there and start to collect

318.664 -> under the damaged endothelium.

321.367 -> Let me actually clear away some of this

323.033 -> because we're going to focus on the cholesterol now.

325.328 -> This is cholesterol and it's going to

326.934 -> sort of settle in here.

329.026 -> It's going to think to itself, hey, that looks pretty comfy.

331.789 -> That looks like a cozy place to be,

334.044 -> so I'm going to just jump in there,

335.335 -> and, of course, these are coming from inside the blood.

337.651 -> They're not just sort of multiplying.

339.723 -> They're floating around in the blood

341.064 -> and then when they come across this damaged

342.69 -> endothelium, they're going to join their friends.

346.021 -> When they build up to this sort of flattened

348.479 -> extent here, they're known as a fatty streak.

352.463 -> One thing that happens to the cholesterol

354.128 -> when they get inside the wall of the blood vessel there

356.87 -> is that they start to get oxidized.

359.37 -> They sort of change a little bit.

361.544 -> When they change, when they get oxidized,

363.982 -> that sends a signal to the immune system,

366.075 -> to our body's immune system,

368.126 -> and that signal will bring around these cells

370.768 -> of the immune system called monocytes.

373.673 -> They'll sort of show up, almost like police.

376.823 -> Here's a monocyte here.

379.342 -> I'll draw it in white to remind you

380.644 -> that it's a white blood cell.

382.553 -> This monocyte doesn't really like

384.157 -> that the cholesterol is starting to collect

385.845 -> in the blood vessel wall, so the monocyte

387.916 -> will actually chase in after the cholesterol

389.643 -> to try to break up the little party that they're having.

392.569 -> I'll actually draw what happens next

394.215 -> down in this next bit of the blood vessel down here,

397.792 -> just so we can keep in mind all of the past events.

401.671 -> You may have noticed that I drew this white

403.378 -> blood cell to look like a Pac-Man sort of thing,

406.628 -> eating up this cholesterol because that's

408.599 -> essentially what it does.

410.387 -> Once it gets into the endothelium,

412.622 -> it converts into something called the macrophage,

415.934 -> macro meaning big and phage meaning to eat.

419.611 -> So it's really this big eater.

422.787 -> It's job here is to devour that LDL cholesterol

426.59 -> that's collected in the endothelium.

429.211 -> Unfortunately, things don't go as planned

431.609 -> for our macrophage, because what ends up happening

434.677 -> is it starts to gorge itself.

436.647 -> The macrophage eats so much cholesterol

439.106 -> that it just sort of becomes too full

441.564 -> of these yellow cholesterol drops

443.616 -> and it sort of dies off,

445.79 -> but it's full of cholesterol.

448.209 -> Someone a long time ago looked

451.046 -> down a microscope and thought that these

452.556 -> dead macrophages filled with cholesterol

455.034 -> looked like foam, like sea foam that you see at the beach,

458.488 -> so these dead macrophages filled with cholesterol

461.495 -> are now called foam cells.

464.461 -> Let's catch our list up.

466.676 -> Remember, these foam cells were actually

468.664 -> white blood cells, so when they die they release

471.59 -> these signals that sort of call in reinforcements.

476.059 -> I'm going to use that to remind you

477.543 -> that atherosclerosis is primarily

480.265 -> an inflammatory disease, it's an inflammatory condition.

484.288 -> When these foam cells release their cytokines,

487.457 -> their signals, they call in reinforcements,

490.261 -> and the whole process sort of proceeds

492.393 -> in this viscous cycle, as you'll see.

495.564 -> Don't forget that LDL is also still being deposited

498.431 -> into the wall from the blood stream.

500.727 -> As part of this inflammation, more and more

502.961 -> endothelial cells get damaged, so I'll move

505.887 -> our drawing down even further so we can look

508.975 -> at the next sort of development.

511.921 -> You can see this mountain of cholesterol

514.768 -> and foam cells, dead macrophages

516.942 -> that are filled with cholesterol.

518.913 -> You can see this mountain just keep on building,

521.635 -> and keep on building, and bulging out

523.951 -> into the middle of the blood vessel.

526.836 -> By now, things are just way out of control.

529.943 -> These guys in here,

531.342 -> this is the smooth muscle part of the artery, by the way,

533.923 -> so this is the smooth muscle layer,

536.706 -> these guys start to take notice,

538.189 -> these smooth muscle cells.

540.607 -> What ends up happening is that you get smooth

542.501 -> muscle cells that sort of migrate

544.37 -> out of the smooth muscle layer,

546.626 -> and they sort of migrate.

548.129 -> I hope you can see this.

549.389 -> I'll draw them a little bit thicker.

551.218 -> They start to migrate out of the smooth muscle layer

554.662 -> and into the fatty plaque here,

559.268 -> because they can sort of sense

560.597 -> that something's not quite right.

563.116 -> What they start to do is they really want the plaque

567.117 -> covered up, because they don't want the thrombogenic --

570.246 -> Remember thrombogenic means clot-forming.

572.665 -> They don't want the thrombogenic plaque

574.961 -> to be exposed to the blood,

577.053 -> so what they start to do is they start

578.577 -> to secrete a fibrous cap.

582.796 -> They sort of spit out this collagen and elastin

586.589 -> protein cap that covers up,

592.268 -> I'm drawing it in purple,

593.453 -> that covers up this plaque

595.709 -> and shields it from the blood stream.

598.086 -> That's called a fibrous cap.

601.336 -> They also do something else.

602.394 -> These smooth muscle also do something else.

605.529 -> You remember these foam cells that died in here.

608.262 -> When they release their signals after they die,

611.187 -> they induce the smooth muscle into depositing

614.032 -> calcium into the plaque.

617.242 -> I'll draw that in.

617.993 -> I'll draw in these little calcium crystals now,

620.899 -> so you can see, it's just starting to look

622.314 -> like a mess in here.

623.824 -> There's just all sorts of stuff going on.

625.615 -> Again, this is really not something

627.667 -> you want to have happening in your body.

630.897 -> Just by looking at this,

632.219 -> what can we say is happening to the blood vessel?

634.84 -> Well, we can see this huge bulge.

638.111 -> We can see that the plaque is obviously

641.402 -> bulging into the blood vessel,

643.392 -> and it's probably going to restrict

645.177 -> the flow of blood that can get through here.

647.965 -> That's one thing that atherosclerosis is doing.

650.335 -> It's occluding, it's blocking off, the arteries.

653.87 -> The second thing is look at this calcium.

656.735 -> If there's one thing that we know about calcium

658.848 -> is that it's really tough, it's really hard.

662.616 -> By the smooth muscle laying down calcium,

665.668 -> that's one of the ways that atherosclerosis

667.964 -> makes your arteries really hard,

669.997 -> and that's actually part of the name.

671.419 -> Atherosclerosis actually means

673.166 -> hardening of your arteries.

675.137 -> But I think in terms of coronary artery disease,

677.472 -> the biggest reason that atherosclerosis is bad

680.216 -> is because it can cause complete blockage of the artery,

685.01 -> and that blockage of the artery can happen

686.982 -> because sometimes this plaque, this fatty plaque,

690.375 -> it can rupture.

691.939 -> When it ruptures, all this thrombogenic plaque

695.169 -> material gets exposed to the blood.

697.363 -> When it gets exposed to the blood,

699.05 -> it starts to form this really big blood clot

701.569 -> in the middle of your artery,

702.97 -> in the middle of one of your coronary arteries.

705.165 -> Let's just draw that in here.

706.445 -> Let's just draw this big blood clot.

707.888 -> Pretend that this has been ruptured,

710.224 -> and this yellow thrombogenic material has been exposed,

713.007 -> and this big blood clot's going to form.

715.73 -> By the way, I'm originally from Jamaica

718.066 -> and blood clot is a bad word in Jamaica,

720.444 -> so I apologize to any of my Jamaicans

723.978 -> who are watching this.

725.665 -> So this big clot could form,

727.006 -> and it could totally block off the blood vessel.

729.729 -> When that happens, no blood can get through, right?

733.02 -> So this is really the biggest reason

734.932 -> that we don't want atherosclerosis

736.984 -> to be happening in our coronary arteries,

739.219 -> because you can see that we've blocked off

741.29 -> the blood flow, and if blood isn't allowed

743.567 -> to get passed this clot and get to the piece

746.94 -> of the heart that it's supposed to be serving

748.971 -> within about 20 minutes, then you get

751.287 -> irreversible damage and death of that piece of heart muscle.

755.188 -> For example, what we drew is this little piece

757.017 -> of artery here, in blue.

759.78 -> So if an atherosclerotic plaque and a clot

763.376 -> developed right there, as it has in our vessel here,

766.911 -> then that would be really, really, really bad,

769.369 -> because all the blood for this whole part of the heart

773.636 -> is coming from this upstream vessel.

776.826 -> So without getting blood flow through this vessel

779.101 -> for about 20 minutes, if this clot persists

782.068 -> for about 20 minutes, all of this heart muscle

785.42 -> would start to die off.

787.614 -> That would be a massive heart attack.

790.438 -> Actually, let me just clarify.

791.73 -> We say heart attack, but in medicine we refer

794.29 -> to a heart attack as a

796.138 -> myocardial infarct, or an MI.

800.14 -> Myocardial just refers to heart muscle,

803.066 -> cardia for heart, and myo for muscle,

806.113 -> so heart muscle.

807.273 -> And infarct means death of tissue

809.466 -> due to lack of oxygen from lack of blood.

812.738 -> So a myocardial infarct is death of heart muscle

816.355 -> due to lack of oxygen.

818.244 -> Here we've had a myocardial infarct

821.434 -> due to this big plaque that developed here.

Source: https://www.youtube.com/watch?v=g3kDdg8r6NY