Post stroke inflammation | Circulatory System and Disease | NCLEX-RN | Khan Academy
Post stroke inflammation | Circulatory System and Disease | NCLEX-RN | Khan Academy
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Content
1.594 -> - [Voiceover] Let me take
you back to that time period,
3.522 -> about four to six hours
after an infarction
6.278 -> when the blood-brain barrier
7.814 -> was just starting to break down,
10.394 -> because I want to talk about
something that's happening
12.398 -> in the ischemic area of the
brain here around that time.
15.64 -> And that something is inflammation.
18.738 -> There's an inflammatory
reaction to the stroke
21.298 -> going on here as well.
23.127 -> And just as a little reminder,
24.691 -> an inflammatory response is sort of
26.495 -> a protective biological
response of tissues.
30.237 -> It happens whenever really anything
32.067 -> sort of irritates your tissues.
34.507 -> So, you know, right now we're
talking about something big,
36.607 -> like inflammation after a stroke.
38.782 -> But, you know, you'd even get
some inflammation happening
40.968 -> when, oh, I don't know, say you get
43 -> a little scratch from your kitty.
44.93 -> So you might notice that even
if the skin isn't broken,
47.652 -> you'd see some swelling and redness
49.684 -> over the scratched area.
52.082 -> And that's some inflammation happening.
54.27 -> And you even get an
inflammatory response happening
56.86 -> when you eat food because, technically,
58.679 -> food is a foreign object
and a potential irritant.
61.686 -> But anyway, I want to focus
63.027 -> on this inflammation for a little bit.
65.469 -> Let's actually follow what happens
66.701 -> with this inflammation from the start,
68.725 -> from the initial ischemia.
70.679 -> And we'll do this in steps.
72.33 -> So step one, ischemia happens,
74.806 -> and it leads to brain cell death, right.
78.171 -> And step two, we haven't
actually seen this step before.
80.788 -> But while the neurons are dying,
83.136 -> they release these little chemical signals
85.411 -> called damage associated
molecular patterns or DAMPS.
89.779 -> So as their name might suggest,
92.199 -> they're these tiny little signals
94.206 -> that let other cells in the area know
97.009 -> that something bad is going on.
99.041 -> And these DAMPS then trigger
an inflammatory response.
103.105 -> So what they do is they activate
104.872 -> these inflammatory cells
called macrophages.
107.466 -> And the macrophages come along.
109.269 -> And, A, they cause more
inflammation to happen.
112.469 -> So they release little signals
114.237 -> to call in all sorts of reinforcements.
116.752 -> And, B, the macrophages
actually directly activate
120.165 -> certain immune cells and get them
122.136 -> involved in the inflammatory response.
124.229 -> And I'm drawing those in in purple now.
126.75 -> So it's this huge sort
of inflammatory response
129.181 -> that's just getting bigger and bigger.
131.424 -> So right now you might be wondering
133.182 -> what the point of this inflammation is.
135.762 -> Well, think about it this way.
137.347 -> All of the brain cells
that were initially dying
139.521 -> and the inflammatory cells
140.862 -> that were first on the scene, right,
142.548 -> they all released little signals
144.316 -> that called in for reinforcements,
146.408 -> i.e., more inflammatory cells.
148.533 -> But once enough backup gets there,
150.727 -> a whole bunch of them sort of switch roles
152.575 -> to being anti-inflammatory cells.
154.892 -> So you can see me turning
156.103 -> these purple inflammatory cells now
157.992 -> into green anti-inflammatory cells.
160.337 -> And the switch to what's called
162.775 -> an anti-inflammatory phenotype
165.402 -> is because, well, a couple of reasons.
167.476 -> First, they don't need any more
reinforcements in the area.
170.593 -> So they stop making sort
of the inflammation worse
172.981 -> by calling in more reinforcements.
175.115 -> And, second, the anti-inflammatory cells
177.35 -> end up acting as the cleanup crew.
179.544 -> So there needed to be a
reasonable number of cells there
182.49 -> to get the cleanup job done,
184.156 -> which actually happens through a process
185.903 -> called liquefactive necrosis.
188.647 -> Before I explain what that is,
190.152 -> let me just update our little step list
192.101 -> over here in the corner.
193.29 -> So step three, the
inflammatory cells come in.
198.438 -> And then step four,
they sort of switch over
200.742 -> to an anti-inflammatory role.
203.93 -> And now step five,
liquefactive necrosis begins.
208.533 -> But let me explain this
liquefactive necrosis thing.
212.644 -> So what it is, first,
neutrophils in the area
215.645 -> will start to release digestive
enzymes called hydrolases.
219.577 -> And these hydrolases, they'll
break down dead cells.
223.034 -> And by doing that, what they
end up creating is this cavity
227.003 -> surrounded by normal, nice, solid tissue,
230.332 -> but this cavity full of sort of soft,
232.94 -> liquified, necrotic cell debris.
236.469 -> And actually I'm gonna zoom out here
238.054 -> because we wanna find out
what happens with this cavity.
241.099 -> And I think it's conceptually a lot easier
243.613 -> to zoom out and look at it
from a macroscopic view.
247.244 -> So let's zoom out a bit.
249.271 -> So here is our guy who's been helping us
251.55 -> learn about strokes this whole time.
253.93 -> And here is the clot.
256.071 -> And here is the ischemic area
in the brain, in this brain.
259.865 -> And just so that we're up to speed here,
261.86 -> so we see the ischemia,
263.687 -> and we know that resulted
in brain cell death.
265.983 -> We know the DAMPS got released.
267.812 -> Then the inflammatory cells
came and did their thing.
270.318 -> And then the liquefactive necrosis began.
273.698 -> And now we want to know
what ends up happening
275.924 -> with our necrotic cavity that
we developed after our stroke.
279.561 -> Well, it can go one of two ways usually.
282.04 -> So if it's a small stroke
283.889 -> and a small subsequent area of necrosis,
287.285 -> it can be walled off.
289.315 -> It can be sort of contained
by a fibrous capsule
292.566 -> and then sort of removed by macrophages.
295.447 -> And notice that when macrophages
297.966 -> remove the junk in this cavity here,
300.77 -> you actually lose some
volume to your brain
303.492 -> since the area doesn't regenerate.
306.821 -> So that's what happens if it's
just a small necrotic area.
310.558 -> But if you have a larger necrotic area,
312.687 -> so let's say if you had a large stroke,
315.951 -> then the area of necrosis
gets sort of walled off again.
320.217 -> It gets quarantined again, if you will,
322.524 -> from the rest of the brain.
324.388 -> And it will become a cyst,
326.441 -> which is a cavity that's separated
328.372 -> from the surrounding tissue.
330.363 -> And then the cyst sort of gets cleaned up
332.943 -> by immune system cells
334.751 -> and just becomes a large cavity,
336.871 -> actually just a hole in the brain
339.959 -> that, A, unfortunately is permanent,
343.393 -> and, B, doesn't sort of regenerate back
346.4 -> into functional brain.
348.411 -> So there's literally a hole that ends up
351.743 -> staying in your brain.
353.916 -> So just for completeness of sake,
355.949 -> step six, cavity formation.
Source: https://www.youtube.com/watch?v=GdfP-loRfm0