Phagocytosis - Video Tutorials & Practice Problems
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concept
Phagocytosis
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2m
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In this video, we're going to begin our lesson on phagocytosis. And so first, we need to recall from some of our previous lesson videos that phagocytosis is the process of cell eating. And so really in this process, cells are going to be engulfing and digesting material that they bring in from the environment. And this includes invading microbes. So it turns out that there are many different types of immune system cells that are capable of phagocytosis. And this includes macrophages, dendritic cells and neutrophils, all which are capable of performing phagocytosis. And so if we take a look at this image that we have down below, notice that it is our map of the lesson on innate immunity. And already in our previous lesson videos, we've talked about the first line defenses, several of the second line defenses, the cells of immunity. And we've talked about the scanning systems, including cell communication pattern recognition receptors and the complement system. And we also mentioned how the complement system can actually serve as a scanning system to detect signs of microbes. But upon activation, it can actually trigger several innate effector actions, several actions. Uh such as for example, phagocytosis and inflammation. And so now in this video, we're starting to transition into this part of the map, the innate effector actions which recall are going to eliminate invaders. And so they serve as uh soldiers that are going to be eliminating invaders. And so the innate effector actions that we're going to talk about moving forward are going to be uh phagocytosis, uh which is again the main focus of this video. And then after we finish talking about phagocytosis and the details of phagocytosis, then we'll move on to talk more about the details of inflammation, the details of fever and the details of the interferon response. But for now, we'll move on to talk more details about phagocytosis. And so this here concludes our brief introduction to phagocytosis. And we'll get to learn more about the steps of phagocytosis in our very next lesson video. So I'll see you all there.
2
concept
Steps of Phagocytosis
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8m
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In this video, we're going to discuss the steps of phagocytosis. And so the process of phagocytosis involves a series of six steps that we have numbered down below one through six. And each of the steps that you see in the text corresponds with the image that we have down below as well. And so in the very first step of phagocytosis is chemotaxis, which recall from some of our previous lesson videos is a process that involves the movement of a cell either towards or away from a chemical. In this case, it's going to be towards a chemical. And so in the very first step of phagocytosis, in the process of chemotaxis, phagocytes are going to be recruited. So phagocytes are going to be recruited to the site of infection by chemo attractants. For example, cytokines like chemokines or C five A is an example of a specific chemo attractant. And so this will allow for phagocytes to move to the site of infection. And so if we take a look at our image down below, notice that it's an image focus on the steps of phagocytosis. And notice that in the very first step of phagocytosis we have chemotaxis. So we can go ahead and label uh this yellow circle as number one because this is the very first step of phagocytosis, chemotaxis. And so chemo attractants are going to be produced. Like for example, C five A here serves as a chemo attractant. And the chemo attractant can be produced either by the microbes themselves as products released by the microbes or the chemo attractants could be released by our own host cells that detect signs of the invading microbes. But either way the chemo attractants are going to be released and that is going to help to attract the fag o site to the location. Now, and the second step of phagocytosis is recognition and attachment. And as its name implies, this is going to be when the phagocyte needs to recognize the invader and bind to the invader. And so phagocytes are going to bind to the microbe, the invading microbe and it can do this directly via MBLS, manos binding lectins uh which will bind to nanos carbohydrates on the surface of microbes or it could bind to the microbes indirectly via sins. Which recall from our previous lesson videos that sins are molecules that will bind to the surface of microbes and allow for optation improved pangs. And so if we take a look at our image down below, notice that the second step of phagocytosis is going to be recognition and attachment. And so notice that this could involve uh obstinance, like for example, C three B can serve as an obstinate to coat the surface of the microbe and allow for improved phagocytose uh uh binding and efficiency. And so, after recognition and attachment, uh the third step of phagocytosis is engulfment. And as its name implies, this is going to be when the phagocyte is going to engulf the microbe. So the phagocyte will send out pseudopods which are these long projections to surround and engulf the material creating what we refer to as a phagosome. And so the phagosome is uh basically just going to be a uh membrane structure that results from phagocytosis that is going to contain the microbe that was phagocytosis. And so if we take a look at our image down below, notice that the third step of phagocytosis is going to be engulfment. And so we can label it with number three. And so notice that the phagocyte which is uh here in blue, this big macrophage right here is going to be able to bind to the microbe using those sins that are coating the microbe and it will use its C three B receptors to again bind to the microbe and get rid of the microbe. Uh and uh ingest the microbe, I should say. And so when this microbe is engulfed, when it is ingested, it is going to be surrounded by a membrane. And that membrane we refer to as the phagosome. So the phagosome is the membrane that results from ingesting the microbe and it's going to contain the microbe. So after engulfment, after the microbe has been engulfed, the fourth step of phagocytosis is going to be phao lysosome formation. And so what's going to happen is that toll like receptors or TLRS that are embedded in the phagosome are going to be able to detect the phagosome contents and uh it will be able to do that before the phagosome fuses with lysosomes. And recall from our previous lesson, videos that lysosomes are cell structures that contain digestive enzymes that are capable of uh destroying and degrading substances. And so if we take a look at our image down below, what we'll see is that the phagosome that results from phagocytosis and contains the microbe is going to fuse with lysosomes in the fourth step. And so the fourth step is going to be Phao lysosome formation. And so the phagosome is going to be the fusion of lysosomes which notice lysosomes are these uh little structures that you can see uh right here in the image and these lysosomes will fuse with the phagosome to form the phao lysosome. And so those digestive enzymes that are contained within the lysosomes will fuse with the phagosome and they will be able to start to degrade and break down the microbe. And that leads us to the fifth step of phagocytosis, which is going to be the destruction and digestion of the microbe. And so the lysosome components, including the hydrolytic enzymes, those digestive enzyme and as well as R OS or reactive oxygen species that are found within the lysosomes. Those are going to degrade the invader as the ph within the phagosome begins to decrease. And so that all helps to degrade the microbe and destroy the microbe. And so notice down below, in the fifth step of phagocytosis, we have the destruction and digestion of the microbe. And so uh notice that the microbe is being completely destroyed within the Phao lysosome. And and the sixth step uh uh of phagocytosis we have is exocytosis. And so what happens is the Phao lysosome is going to fuse with the cells cytoplasmic membrane to release the debris that resulted from the degradation of the micro. And so notice down below and the sixth and final step down below right here. Uh we have exocytosis and so the phagosome will fuse with the cell cytoplasmic membrane and will release the degraded microbe. And so now the microbe is no longer capable of causing us harm and we will be able to eliminate it from our bodies after this process. And so um in the case that the invading microbes are actually not cleared immediately, it is also possible for these macrophages or phagocytes uh to produce cytokines and uh those cytokines can uh continue to recruit more and more phagocytes over time. So more and more phagocytes will be recruited to the location so that all of those phagocytes can work together to eliminate all of the microbes in the infected area. And so this here concludes our brief lesson on the steps of phagocytosis. And something that's important for you to be able to understand is uh the order of these steps. That is something that you should be able to do as you prepare for one of your microbiology exams on this process. And so make sure that you're able to put these steps in the correct order. And so this here concludes our brief lesson on the steps of phagocytosis. And we'll be able to apply these concepts as we move forward. So I'll see you all in our next video.
3
Problem
Problem
Where are bacteria killed by enzymes and toxic substances once ingested by a white blood cell?
A
Nucleus.
B
Phagolysosome.
C
Lysosome.
D
Cytoplasm.
E
Phagosome.
4
Problem
Problem
Which of the following statements about phagosomes and phagolysosomes are true?
A
Phagosomes are vesicles surrounding an engulfed microbe.
B
Phagosomes can be found in neutrophils, macrophages, and T cells.
C
Phagolysosomes destroy the engulfed microbe with digestive enzymes.
D
Phagolysosomes are the fusion of a phagosome and a lysosome.
E
A and C.
F
B and D.
G
A, C, and D.
H
All of the above.
5
Problem
Problem
Which of the following statements about phagocytosis is incorrect?
A
Digestion of the pathogen occurs in the phagolysosome.
B
Cells capable of phagocytosis have receptors that recognize C3b proteins or antibodies bound to the pathogen.
C
Cells capable of phagocytosis move toward the infected area of the body via chemotaxis.
D
Macrophages die after phagocytosis of a pathogen while neutrophils regenerate and survive.