Role of phagocytes in innate or nonspecific immunity | NCLEX-RN | Khan Academy — Transcript

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1. 0:00The whole point of the immune system is to keep out shady
2. 0:08things from your body-- or, if they get in, to kill them.
3. 0:10So those shady things would include shady proteins that
4. 0:15can do damage to your body, viruses, bacteria, even
5. 0:23eukaryotic parasites, and then even fungi.
6. 0:31So all sorts of things that if they were to enter your body,
7. 0:34they would cause some form of disease.
8. 0:37These are collectively called pathogens.
9. 0:41So the whole point of the immune system is, on a first
10. 0:44line of defense, keep these things out-- and then if they
11. 0:47were to get into your body, to kill and eliminate them from
12. 0:51our system so that we don't get sick and so
13. 0:53that we don't die.
14. 0:54So I already just mentioned that there's kind of two lines
15. 0:57of defense and even with those, there's kind of
16. 0:59subclassifications.
17. 1:01The first line of defense-- I'll just call that the first
18. 1:03line-- which is essentially just to keep things out-- keep
19. 1:10all of these pathogens out.
20. 1:12And there's some obvious ones.
21. 1:14There's our skin.
22. 1:15Our skin keeps pathogens out and actually even the oils on
23. 1:19our skin are a little bit more acidic and it's hard for some
24. 1:22types of bacteria to thrive in that type of environment.
25. 1:27You have your mucus membranes and in the mucus, there's
26. 1:35there's some chemicals that maybe make it a little bit
27. 1:37more difficult for bacteria to survive.
28. 1:40And then you even have acidic environments like
29. 1:43your stomach acid.
30. 1:48You might not view your stomach as the outside of you,
31. 1:52but it fundamentally is.
32. 1:53Your whole digestive tract, which I'll make videos on in
33. 1:55the near future, is really on the outside of you.
34. 1:58You can simply model really most vertebrate bodies as kind
35. 2:04of a doughnut our digestive tract is the
36. 2:07inside of the doughnut.
37. 2:08So stomach acid is on the outside of our real bodies and
38. 2:14you can imagine, that's a hard environment for a lot of these
39. 2:16pathogens to survive in.
40. 2:18So that's the first line of defense, but we know that
41. 2:20that's not good enough, that sometimes these things can get
42. 2:24into our bodies, and there we have to start thinking about
43. 2:27the second line of defense.
44. 2:30What do we do once things are actually in our body?
45. 2:44And here, in both the first and second line, I'm talking
46. 2:48about non-specific immunity-- and this is going to make a
47. 2:51lot of sense when we start talking about specific
48. 2:54immunities.
49. 2:54So both of these are non-specific.
50. 3:00And when I say non-specific-- or you can also call them
51. 3:03innate-- it means that they just generally respond to
52. 3:09things that appear bad.
53. 3:11They don't remember the bad things that came before.
54. 3:13They don't respond to a particular type of virus or a
55. 3:16particular-- well, they do respond to every type of virus
56. 3:20or every type of bacteria, but they don't say, this is virus
57. 3:23type A, B, C, or this is bacteria type A, B, C.
58. 3:26They just say, this is a virus.
59. 3:27Let me get rid of it, or let me not let it in.
60. 3:30This is a bacteria.
61. 3:31Let me get rid of it or let me not let it in.
62. 3:33It doesn't know what type of bacteria it's dealing with.
63. 3:36So this is all the non-specific or
64. 3:39innate immune system.
65. 3:41And we'll go into a lot of detail on the specific immune
66. 3:44system because you can imagine, it becomes very
67. 3:45complicated or interesting when you start thinking about
68. 3:48your body somehow remembering a virus that it's seen before
69. 3:51and being able to respond better to that virus or that
70. 3:53bacteria or that protein the second time it sees it.
71. 3:57So we're dealing with non-specific in this case.
72. 3:59And the the second line of your non-specific immunity,
73. 4:04there are two things.
74. 4:04One is an inflammatory response.
75. 4:16And I'm going to do a whole video on this, but in general,
76. 4:20we've all experienced inflammatory responses.
77. 4:23When you see blood flowing to a certain part of an area and
78. 4:26you see there's pus and there's-- and I'm going to go
79. 4:28into a lot more detail on what an inflammatory response
80. 4:30actually is, but that's one of your-- and what it really is
81. 4:33doing is bringing blood and bringing cells that can fight
82. 4:37whatever type of infection you have. It's bringing them to
83. 4:41the site where maybe you got a cut or maybe where a lot of
84. 4:45the bacteria or whatever the pathogen is.
85. 4:47So inflammatory response is all about bringing fluid and
86. 4:50fighters to the fight.
87. 4:55I'm going to do a whole video on that.
88. 5:07But the byproduct is, that part of your tissue or that
89. 5:10part of you body gets inflamed-- a lot of fluid
90. 5:12there, a lot of byproducts of the battle that goes on there.
91. 5:16We'll do a whole video on that.
92. 5:18And the other second line of defense is, and it's actually
93. 5:20part of the inflammatory response-- are phagocytosis or
94. 5:24phagocytes.
95. 5:28And really, what I want to do over the rest of this video is
96. 5:31talk in a little bit more detail about phagocytes
97. 5:34because once we understand what phagocytes do, that's a
98. 5:37pretty good building block for going into the specific immune
99. 5:42system-- and actually, it'll help lead into the discussion
100. 5:45on the inflammatory response as well because phagocytes are
101. 5:47really part of the inflammatory response.
102. 5:51So phagocytes are just a class of cell
103. 5:54that can eat up pathogens.
104. 5:56They can eat up other things really, but when we talk about
105. 5:59the immune system, we're talking about pathogens.
106. 6:00So let's say that this is a phagocyte right here.
107. 6:04This is a phagocyte right there.
108. 6:07It has some kind of a nucleus, whatever.
109. 6:09I don't have to focus on the inside of the phagocyte.
110. 6:12It's a traditional eukaryotic cell, but what I want to do is
111. 6:16see what happens when a phagocyte encounters a foreign
112. 6:20particle or a foreign bacteria.
113. 6:22So let me say this is a foreign bacteria right here.
114. 6:26So the phagocyte, we've already said, is non-specific.
115. 6:29What it does is, it has receptors that respond to just
116. 6:32things that it knows are bad.
117. 6:34You could imagine these are super sensors.
118. 6:43Maybe these are super sensors for bacteria.
119. 6:45The bacteria have proteins on their surface that maybe look
120. 6:48something like that.
121. 6:48Obviously they don't look exactly like that.
122. 6:50I'm just drawing them as kind of a Y and a triangle so you
123. 6:53can see that they fit.
124. 6:54But once these two guys connect-- let me draw the
125. 6:59situation where they have connected.
126. 7:02So this is the bacteria.
127. 7:03This is the pathogen.
128. 7:04And it's really the same idea with a virus or any
129. 7:06other type of thing.
130. 7:07And we'll actually see in future videos that these guys
131. 7:10can actually be tagged by other molecules, which makes
132. 7:13these phagocytes want to attack them even more.
133. 7:17Once they're bonded-- that's my bacteria,
134. 7:20the invading pathogen.
135. 7:21And now it is bonded.
136. 7:25It has triggered the receptor on this phagocyte.
137. 7:28This phagocyte will start to engulf-- it'll wrap around
138. 7:34this pathogen.
139. 7:44And these two ends are eventually going to meet.
140. 8:00But then once these two meet, what's it going to look like?
141. 8:03Then all of a sudden, that bacteria is going to be
142. 8:09completely engulfed.
143. 8:10It's going to be inside of the cell.
144. 8:11So now the cell-- once these two ends meet and these
145. 8:15membranes merge, then this guy is going to be in his own
146. 8:19little membrane bubble-- or you can almost imagine, it's
147. 8:21in its own little vesicle.
148. 8:23So this is the pathogen, the bacteria in this case-- but
149. 8:28phagocytosis-- the process is completely identical in terms
150. 8:31of how it engulfs things.
151. 8:33If it was a virus or some type of other foreign protein or
152. 8:37any type of really foreign molecule-- actually, sometimes
153. 8:42it doesn't even occur to foreign stuff.
154. 8:43It can occur to dying molecules that are not
155. 8:47foreign, that just need to be cleared out.
156. 8:49But we'll just focus on the immune system, on foreign
157. 8:51things right now.
158. 8:54So this membrane right here will completely merge and go
159. 8:58around this guy like this.
160. 9:01And of course, you had your receptors and who knows if
161. 9:03they're still there.
162. 9:04By the time-- let's just draw them there so you see that
163. 9:07that part is that part.
164. 9:08But once it's fully engulfed, this thing is called a
165. 9:11phagosome, on which is really just a vesicle that contains
166. 9:20that foreign particle that you want to get rid of.
167. 9:22And then other fluid or vesicles that contain things
168. 9:33that can eat up this phagosome-- so let's say that
169. 9:38this is some vesicle that contains things-- lysozymes
170. 9:43and it contains really reactive species of oxygen.
171. 9:50And if this comes in contact with, really, almost any
172. 9:52biological compound, it's going to do some damage.
173. 9:55But once the pathogen is completely merged inside the
174. 10:00cell, this little package will merge over here and it will
175. 10:06dump its contents into this phagosome, into this vesicle
176. 10:11containing the pathogen, and then break it up.
177. 10:15It's essentially digesting it.
178. 10:18So obviously the first role is, it just got it out of the
179. 10:21way and it killed it.
180. 10:22And then the second role-- and I'm just going to give a
181. 10:24little tidbit right here.
182. 10:26We're going to do it in a lot more detail in future videos.
183. 10:28It breaks it up.
184. 10:38So now the thing is all broken up.
185. 10:45So that thing is broken up into constituent proteins and
186. 10:48another molecules.
187. 10:50And then what the phagocyte does-- it'll actually take
188. 10:57some subset of these molecules, some
189. 11:02subset of the proteins.
190. 11:02It'll break them out.
191. 11:04Proteins are just sequences of amino acids.
192. 11:06Normally when people say proteins, they're talking
193. 11:08about long sequences of amino acids.
194. 11:10When people talk about short sequences of amino acids or a
195. 11:13protein that's broken up a lot, they refer to it as a
196. 11:16peptide chain.
197. 11:17A peptide chain is a shorter chain of amino acids.
198. 11:20So this guy will take some special peptide chains, some
199. 11:22special pieces from the thing it just killed, attach them to
200. 11:28some other proteins.
201. 11:29So it'll take maybe a little piece of this bacteria right
202. 11:37now, attach it to other protein, which is called a
203. 11:45major histocompatibility complex-- and if we're talking
204. 11:48about phagocytes, this will be a major histocompatibility
205. 11:52complex type II.
206. 11:59It sounds very-- a strange word, but we're going to see
207. 12:01this a lot.
208. 12:17So they abbreviate it MHC.
209. 12:20This is a protein and it bonds with this peptide that was
210. 12:24kind of chunked off or digested off of this invading
211. 12:27pathogen and then this phagocyte will then present it
212. 12:32onto its membrane.
213. 12:33So this combination-- the complex of the MHC-- in this
214. 12:37case, it's going to be an MHC II protein.
215. 12:44We're going to talk about Type I in the future.
216. 12:46It's going to take this complex and then present it on
217. 12:49its surface.
218. 13:01And the reason why I'm going through all this pain of
219. 13:05explaining this process-- you're like, hey, we already
220. 13:06got rid of the thing and killed it.
221. 13:08Why is Sal worried about what we do with the peptides?
222. 13:11This is crucial to our immune system because we'll see other
223. 13:14specific parts of our immune system.
224. 13:16Remember, so far everything is non-specific.
225. 13:19This guy just said, this is an invader.
226. 13:21It doesn't know the type of an invader.
227. 13:22It just says, hey, let me bond to this thing and kill it.
228. 13:26It's one of these things that I know are foreign to my body.
229. 13:30So it kills it, but now it can leave it on its surface and
230. 13:33now the specific parts, the parts that actually have
231. 13:36memory and attack specific things, can say, gee, Mr.
232. 13:40Phagocyte, look, you've killed something.
233. 13:42Let me see if I have some specific reactions that can be
234. 13:46triggered by this thing that you're presenting.
235. 13:48So, many phagocytes are also called
236. 13:51antigen presenting cells.
237. 14:00And I'm going to go into more detail on what exactly an
238. 14:03antigen is.
239. 14:04I called this thing a pathogen.
240. 14:06An antigen is essentially-- you can view it as a protein
241. 14:10or a peptide chain that will trigger or that can be dealt
242. 14:15with within the immune system.
243. 14:16I'll be a little bit-- the specific immune system.
244. 14:19And I'm going to be a little bit more nuanced about it when
245. 14:22I talk-- I'll make a whole video on antigens and
246. 14:24antibodies, but right now you can just view it as a peptide
247. 14:27chain right there.
248. 14:28An antigen is just a protein or part of a protein.
249. 14:31So this is presenting an antigen on its surface that
250. 14:34can later be used by other parts.
251. 14:37Now, the one thing that-- there are many, many types of
252. 14:41phagocytes.
253. 14:42And just to give you-- just so when you see different words,
254. 14:45you don't get confused by the different types of phagocytes.
255. 14:48I'll do a little review of those right now.
256. 14:50You have neutrophils.
257. 14:54These are actually the most common of the phagocytes.
258. 14:58And these are the fast and numerous respondors.
259. 15:01So these get to a location of infection very fast.
260. 15:10Phagocytes don't necessarily just have to kill in this way.
261. 15:13I mean, they're called phagocytes because they engulf
262. 15:15this way, but we'll in future videos talk about other ways
263. 15:17that they can release chemicals or even DNA nets to
264. 15:20ensnare pathogens, but neutrophils
265. 15:23are fast and abundant.
266. 15:25And then you have macrophages, which are-- on some level,
267. 15:30they're the most versatile and do the heavy lifting, but
268. 15:32they're also phagocytes.
269. 15:34And then you dendritic cells.
270. 15:38And when you first see the word dendritic cell, you
271. 15:40think, hey, does this somehow relate to dendrites of the
272. 15:42nervous system?
273. 15:43And no, they have nothing to do with the nervous system.
274. 15:52The reason why they're called dendritic cells is because
275. 15:54they look like they have dendrites.
276. 16:03So they look like neurons on some level, but they don't
277. 16:05participate in the nervous system at all.
278. 16:08And these tend to be the best activators of the specific
279. 16:11immune system that we'll talk about in future videos.
280. 16:14So anyway, I'll leave you there and we'll talk more
281. 16:16about all of this in the next few videos.