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

The whole point of the immune
system is to keep out shady things from your body– or, if
they get in, to kill them. So those shady things would
include shady proteins that can do damage to your body,
viruses, bacteria, even eukaryotic parasites,
and then even fungi. So all sorts of things that if
they were to enter your body, they would cause some
form of disease. These are collectively
called pathogens. So the whole point of the immune
system is, on a first line of defense, keep these
things out– and then if they were to get into your body, to
kill and eliminate them from our system so that we don’t
get sick and so that we don’t die. So I already just mentioned that
there’s kind of two lines of defense and even with
those, there’s kind of subclassifications. The first line of defense– I’ll
just call that the first line– which is essentially just
to keep things out– keep all of these pathogens out. And there’s some obvious ones. There’s our skin. Our skin keeps pathogens out and
actually even the oils on our skin are a little bit more
acidic and it’s hard for some types of bacteria to thrive in
that type of environment. You have your mucus membranes
and in the mucus, there’s there’s some chemicals that
maybe make it a little bit more difficult for bacteria
to survive. And then you even have acidic
environments like your stomach acid. You might not view your stomach
as the outside of you, but it fundamentally is. Your whole digestive tract,
which I’ll make videos on in the near future, is really
on the outside of you. You can simply model really most
vertebrate bodies as kind of a doughnut our digestive
tract is the inside of the doughnut. So stomach acid is on the
outside of our real bodies and you can imagine, that’s a hard
environment for a lot of these pathogens to survive in. So that’s the first line of
defense, but we know that that’s not good enough, that
sometimes these things can get into our bodies, and there we
have to start thinking about the second line of defense. What do we do once things are
actually in our body? And here, in both the first and
second line, I’m talking about non-specific immunity–
and this is going to make a lot of sense when we start
talking about specific immunities. So both of these are
non-specific. And when I say non-specific–
or you can also call them innate– it means that they
just generally respond to things that appear bad. They don’t remember the bad
things that came before. They don’t respond to a
particular type of virus or a particular– well, they do
respond to every type of virus or every type of bacteria, but
they don’t say, this is virus type A, B, C, or this is
bacteria type A, B, C. They just say, this
is a virus. Let me get rid of it, or
let me not let it in. This is a bacteria. Let me get rid of it or
let me not let it in. It doesn’t know what type of
bacteria it’s dealing with. So this is all the
non-specific or innate immune system. And we’ll go into a lot of
detail on the specific immune system because you can imagine,
it becomes very complicated or interesting when
you start thinking about your body somehow remembering a
virus that it’s seen before and being able to respond better
to that virus or that bacteria or that protein the
second time it sees it. So we’re dealing with
non-specific in this case. And the the second line of your
non-specific immunity, there are two things. One is an inflammatory
response. And I’m going to do a whole
video on this, but in general, we’ve all experienced
inflammatory responses. When you see blood flowing to a
certain part of an area and you see there’s pus and
there’s– and I’m going to go into a lot more detail on what
an inflammatory response actually is, but that’s one of
your– and what it really is doing is bringing blood and
bringing cells that can fight whatever type of infection you
have. It’s bringing them to the site where maybe you got a
cut or maybe where a lot of the bacteria or whatever
the pathogen is. So inflammatory response is all
about bringing fluid and fighters to the fight. I’m going to do a whole
video on that. But the byproduct is, that part
of your tissue or that part of you body gets inflamed–
a lot of fluid there, a lot of byproducts of
the battle that goes on there. We’ll do a whole
video on that. And the other second line of
defense is, and it’s actually part of the inflammatory
response– are phagocytosis or phagocytes. And really, what I want to do
over the rest of this video is talk in a little bit more
detail about phagocytes because once we understand what
phagocytes do, that’s a pretty good building block for
going into the specific immune system– and actually, it’ll
help lead into the discussion on the inflammatory response as
well because phagocytes are really part of the inflammatory
response. So phagocytes are just
a class of cell that can eat up pathogens. They can eat up other things
really, but when we talk about the immune system, we’re talking
about pathogens. So let’s say that this is
a phagocyte right here. This is a phagocyte
right there. It has some kind of a
nucleus, whatever. I don’t have to focus on the
inside of the phagocyte. It’s a traditional eukaryotic
cell, but what I want to do is see what happens when a
phagocyte encounters a foreign particle or a foreign
bacteria. So let me say this is a foreign
bacteria right here. So the phagocyte, we’ve already
said, is non-specific. What it does is, it has
receptors that respond to just things that it knows are bad. You could imagine these
are super sensors. Maybe these are super sensors
for bacteria. The bacteria have proteins on
their surface that maybe look something like that. Obviously they don’t look
exactly like that. I’m just drawing them as kind
of a Y and a triangle so you can see that they fit. But once these two guys
connect– let me draw the situation where they
have connected. So this is the bacteria. This is the pathogen. And it’s really the same idea
with a virus or any other type of thing. And we’ll actually see in future
videos that these guys can actually be tagged by other
molecules, which makes these phagocytes want to
attack them even more. Once they’re bonded–
that’s my bacteria, the invading pathogen. And now it is bonded. It has triggered the receptor
on this phagocyte. This phagocyte will start to
engulf– it’ll wrap around this pathogen. And these two ends are
eventually going to meet. But then once these two meet,
what’s it going to look like? Then all of a sudden, that
bacteria is going to be completely engulfed. It’s going to be inside
of the cell. So now the cell– once these
two ends meet and these membranes merge, then this guy
is going to be in his own little membrane bubble– or you
can almost imagine, it’s in its own little vesicle. So this is the pathogen, the
bacteria in this case– but phagocytosis– the process is
completely identical in terms of how it engulfs things. If it was a virus or some type
of other foreign protein or any type of really foreign
molecule– actually, sometimes it doesn’t even occur
to foreign stuff. It can occur to dying molecules
that are not foreign, that just need
to be cleared out. But we’ll just focus on the
immune system, on foreign things right now. So this membrane right here will
completely merge and go around this guy like this. And of course, you had your
receptors and who knows if they’re still there. By the time– let’s just draw
them there so you see that that part is that part. But once it’s fully engulfed,
this thing is called a phagosome, on which is really
just a vesicle that contains that foreign particle that
you want to get rid of. And then other fluid or vesicles
that contain things that can eat up this phagosome–
so let’s say that this is some vesicle that
contains things– lysozymes and it contains really reactive
species of oxygen. And if this comes in contact
with, really, almost any biological compound, it’s
going to do some damage. But once the pathogen is
completely merged inside the cell, this little package will
merge over here and it will dump its contents into this
phagosome, into this vesicle containing the pathogen,
and then break it up. It’s essentially digesting it. So obviously the first role is,
it just got it out of the way and it killed it. And then the second role– and
I’m just going to give a little tidbit right here. We’re going to do it in a lot
more detail in future videos. It breaks it up. So now the thing is
all broken up. So that thing is broken up into
constituent proteins and another molecules. And then what the phagocyte
does– it’ll actually take some subset of these
molecules, some subset of the proteins. It’ll break them out. Proteins are just sequences
of amino acids. Normally when people say
proteins, they’re talking about long sequences
of amino acids. When people talk about short
sequences of amino acids or a protein that’s broken up a lot,
they refer to it as a peptide chain. A peptide chain is a shorter
chain of amino acids. So this guy will take some
special peptide chains, some special pieces from the thing it
just killed, attach them to some other proteins. So it’ll take maybe a little
piece of this bacteria right now, attach it to other protein,
which is called a major histocompatibility
complex– and if we’re talking about phagocytes, this will be
a major histocompatibility complex type II. It sounds very– a strange word,
but we’re going to see this a lot. So they abbreviate it MHC. This is a protein and it bonds
with this peptide that was kind of chunked off or digested
off of this invading pathogen and then this phagocyte
will then present it onto its membrane. So this combination– the
complex of the MHC– in this case, it’s going to be
an MHC II protein. We’re going to talk about
Type I in the future. It’s going to take this complex
and then present it on its surface. And the reason why I’m going
through all this pain of explaining this process– you’re
like, hey, we already got rid of the thing
and killed it. Why is Sal worried about what
we do with the peptides? This is crucial to our immune
system because we’ll see other specific parts of our
immune system. Remember, so far everything
is non-specific. This guy just said, this
is an invader. It doesn’t know the type
of an invader. It just says, hey, let me bond
to this thing and kill it. It’s one of these things that I
know are foreign to my body. So it kills it, but now it can
leave it on its surface and now the specific parts, the
parts that actually have memory and attack specific
things, can say, gee, Mr. Phagocyte, look, you’ve
killed something. Let me see if I have some
specific reactions that can be triggered by this thing that
you’re presenting. So, many phagocytes
are also called antigen presenting cells. And I’m going to go into more
detail on what exactly an antigen is. I called this thing
a pathogen. An antigen is essentially– you
can view it as a protein or a peptide chain that will
trigger or that can be dealt with within the immune system. I’ll be a little bit– the
specific immune system. And I’m going to be a little bit
more nuanced about it when I talk– I’ll make a whole
video on antigens and antibodies, but right now you
can just view it as a peptide chain right there. An antigen is just a protein
or part of a protein. So this is presenting an antigen
on its surface that can later be used
by other parts. Now, the one thing that– there
are many, many types of phagocytes. And just to give you– just so
when you see different words, you don’t get confused by the
different types of phagocytes. I’ll do a little review
of those right now. You have neutrophils. These are actually the most
common of the phagocytes. And these are the fast and
numerous respondors. So these get to a location
of infection very fast. Phagocytes don’t necessarily
just have to kill in this way. I mean, they’re called
phagocytes because they engulf this way, but we’ll in future
videos talk about other ways that they can release chemicals
or even DNA nets to ensnare pathogens,
but neutrophils are fast and abundant. And then you have macrophages,
which are– on some level, they’re the most versatile and
do the heavy lifting, but they’re also phagocytes. And then you dendritic cells. And when you first see the
word dendritic cell, you think, hey, does this somehow
relate to dendrites of the nervous system? And no, they have nothing to
do with the nervous system. The reason why they’re called
dendritic cells is because they look like they
have dendrites. So they look like neurons on
some level, but they don’t participate in the nervous
system at all. And these tend to be the best
activators of the specific immune system that we’ll talk
about in future videos. So anyway, I’ll leave you there
and we’ll talk more about all of this in the
next few videos.

100 Replies to “Role of phagocytes in innate or nonspecific immunity | NCLEX-RN | Khan Academy”

  1. Glad I uncovered this vid. Love You tube due to this kind of info…

    My homeboy had been bullied. He said he was planning to grow muscle and strength. I did not believe him. Til out of nowhere he gained 40 pounds of full-strength muscle mass. He used the Muscle Building Bible – look for it in Google. Nobody dares to intimidate him anymore. I personally registered the other day. See what goes on. And this guys emails are fucking fascinating!

  2. I wish when he said 'let me draw the situation' he just drew that douche off of jersey shore, it would have thrown everyone off and there would be loads of confused examiners in summer like hey wtf is this guy doing here?!

  3. You are amazing khan. I was finding hard to understand it but now I completely get it within 16mins. I have an exam soon and I am more confident that I will get that first class in immunology. I can't thank you enough

  4. i actually did — Khan. S (2010). Role of Phagocytes in Innate or Nonspecific Immunity (Online). Available at: [accessed: dd/mm/year/

  5. Khan Academy is Amazing! I learn so much and i find myself finding for videos like these to keep my study track on track. Thank you so much. makes me understand it in the simplest form for my exam.

  6. Yo yo… Superb movie. My close friend was once a fatty. He improved his body from 284lbs of fat into 211 lbs of purely natural muscle mass. Everybody was in shock. I just subscribed myself coz I'm trying to get bigger muscle mass. He made use of the Muscle Building Bible (Look in Google)…

  7. At the end, can they also use exocytosis to release the bacteria/lysosomes instead of becoming an APC? (Anyone please confirm/deny my question if it's different circumstances or if I'm wrong! – thanks)

  8. so are MHC II inside the phagocyte?? so when the phagocyte engulfs the bacteria, it breaks it down into peptides, then uses those peptides to give to MHC II which then present it on the outside of the phagocyte for other cells to recognise 

  9. THANK YOU SO MUCH!!! I watched all your videos regarding the immune response and it was extremely helpful! I am no longer absolutely confused. I finally understand it. I want you to know that you're AMAZING! Thank you!!!!!!!!!! 🙂 🙂 🙂

  10. Sir, whoever you are…. you are amazing!   I'm taking advanced pathophysiology in grad school.  Your videos on Khan Academy are the best!!  Thank you for sharing your God given gift for teaching!!

  11. this video is very good…. Thanks! however, in future…would it be possible to use more "medical" terms throughout the video? Thanks 🙂

  12. Khan, you are better than this. Be more specific. I wouldn't have indicated monocyte cells found underneath the skin to be dendritic cells. I would have rather articulated the latter to be langerhans cells. Monocytes found underneath the skin are called langerhans cells. Monocytes found in the lymph nodes and spleen are dendritic cells. Let me know if you disagree. Thanks.

  13. I was starting to believe that Medicine (especially because of Ana Path) is not my thing untill i staterted watching your videos. Much appreciation. Keep it up Sir.

  14. I think this for high school level biology – college freshmen level general biology. Khan is definitely not the greatest biologist, I saw him making mistakes in other biology videos. He is much better in other fields. This video can be great if you want to get the big picture.

  15. Appreciate these videos Kahn. Have my AP bio exam next week and there are some chapters we haven't reviewed. These are A LOT of help!

  16. It's not too important, but the part of the immune system you're referring to as the "first line of defense" that keeps pathogens out is called the integumentary system. It's different from the immune system because it prevents pathogens from entering, whereas the immune system is internal. Thanks for the video anyway.

  17. is there any way to get PDFs of these notes? I don't mind copying them down but I am seemingly doing it for every single video you have :'(

  18. Sal you are literally amazing. I watch your math videos, I didn't even know there were Immunology videos and I almost jumped for joy when I saw them.

  19. THANK YOU VERY MUCH. I am from Spain , and in order to enter university we must do an exam with tons of biology info and you literally saved me, you have all kinds of videos about biology including every single chapter of my giant book hahahah !!!

  20. Your videos are soo helpful. I remember passing most of my math classes because of Khan Academy. Now for my pathophysiology class, your videos are so much more helpful than the book or the lecture. Not sure why I am paying my school.
    Thank you.

  21. PHAGOCYTES are like (the) HOMELAND SECURITY for our immune system, so to speak…. and now this new pathogen is on their "watch list"………

  22. If phagocytosis is 2nd line of defense shouldn't it be non-specific? then, how come receptor of phagocytes need to match with the markers of the antigen?

  23. Among all lecturers in Khan Academy, I love this lecturer the most. The way he explains is really helpful (in comparison to some lecturers in Khan ; don't really like the female lecturer whose voice is a lil' fake and uncomfortable to listen to.

  24. The ability of Doctors to Understand that Cancer is a Totally Curable or Reversible Pathology depends on them understanding early on (the expensive and treacherous journey of medial indoctrination) the fact that Cancer is a Failure of the Immune System to Eliminate these Abnormally Growing Cells rather than An Exclusive Genetic Mutation Anomaly.

  25. Again, Sal, how does the phagocyte know the particle is foreign and unwanted? Last I knew phagocytes do not have brains and cannot learn. "Things that it knows are bad" That begs the question: HOW does it know the thing is bad?

  26. Its it that the dendritic cells used fr treatment of brain tumors? How is it nt related to the dendrites???

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