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Let's talk about exactly how flu causes so much damage

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to ourselves and why it makes us feel

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so lousy whenever we get the flu.

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And I start up with drawing the flu virus here.

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This is our influenza virus,INFLUENZA VIRUS.

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And we have on influenza a couple of features

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that we have to remember.

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So you know, on the out side there is a sort of envelope.

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And what's on the inside of this envelope

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are 8 bits of RNA, 8 pieces of RNA.

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And so this RNA is important to remember

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because in the human cell in our cells, I'm going to draw one of our cells right here,

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we have instead of RNA we have DNA, remember.

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And so this is our nucleus.

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And on the inside of the nucleus is our DNA.

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So this is our DNA over here.

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So the virus has RNA and we have DNA.

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In the outside of the human cell, I should have been labelling this over here, this is HUMAN CELL.

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The outside of the human cell has something called

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SIALIC ACID

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There are these little strings over here. They are coming of

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and I'm drawing them far larger than they are in real life.

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They're not nearly this big.

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But there are these little, tiny little things called sialic acid.

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And this sialic acid becomes very important in understanding how the influenza virus

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gets into and out of our cells

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So the outside, remember, of the influenza virus there were couple of proteins

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And I'm gonna draw one of these proteins here.

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I'm gonna make it look like a hand.

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So this is a little hand and this protein is called HEMAGGLUTININ

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In fact previously I called the H protein and you can call that if you want.

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But the full name is hemagglutenin.

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And what hemagglutenin does is that it actually holds onto sialic acid.

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In fact that's an easy way to remember, right, because H and H go together

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It holds sialic acid.

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That becomes very important because that allows it the first step towards getting into the cell

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That is another protein on the outside here.

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I'm gonna make it look like a pair of scissors.

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Because it will kind of remind us what this one does.

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And this is called neurominidase.This one is called neurominidase.

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And I'm gonna pass on explaining what it does just for the moment.

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I'll tell you a little bit what it does.

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So then the first step to get into the cell is for hemagglutinin to hold on sialic acid.

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And than there are few other small molecular steps that happen,

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important ones but I'm gonna suffice to say gets inside.

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And once the influenza virus gets inside,

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these are RNA segments they're let loose.

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So these segments are gonna start making their way towards the nucleus.

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So once they get into the nucleus they are in the same kind of area that DNA is.

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And what they do is remarkable.

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They basically take over.

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These little RNA start making many copies of themselves.

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And what they want to do is make our human cell into a factory.

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They want to make a factory and this factory is gonna make little proteins, viroproteins.

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And it's gonna make viral RNA.

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And what it's not gonna do the one thing that cell is no longer gonna to be very good at doing

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is its normal job.

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So the human cell of course had some job to do

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and it's not gonna have the resources or the time to do it

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because it's basically been taken over by this viral RNA.

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So what happens then is that the viral RNA is basically turned into a factory and

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what it wants to do is make more and more copies of it selves.

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Let me just show you what that would look like.

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Here is a daughter cell, lets say it goes over here.

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And I'm gonna clean this up a little bit, just to make sure that we're looking at a nice and neat picture.

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Let's say something like this.

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So this is our daughter cell on the other side.

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And these cells are gonna try to make their way out of the human cell, right?

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Because now they're a package, they are ready to go.

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And where these suppose they wanna go next?

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Where they gonna wanna find their own human cell to invade.

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Because they wanna to continue this process.

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We've got more human cells over here down below.

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We've got maybe let's say one human cell up here.

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So we've got new targets for this virus.

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And this virus is going to seek out these targets and try to make its way inside

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again using its hemagglutinin.

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But before it can do that it's gotta break loose, right?

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Because it's still attached to that sialic acid.

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It's here where neurominidase comes in.

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And neurominidase it basically, it nicks.

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And there is with the N is helpful for remembering it.

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It nicks or cuts sialic acid.

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It's if a nicker cut that sialic acid it can break free.

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As I remember the two proteins as hemagglutinin holds sialic acid to enter the cell

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that is on entry and the neuraminidase is gonna nick the sialic acid

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and that important for exiting the cell.

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But we still haven't answered the question : how does all this cause our symptoms?

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or what happens is as these cells get turned into factories

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they start dying or getting damaged.

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And all their content start leaking out.

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So all these contents from the cell start leaking out and as they do they create inflammation.

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Let me bring a little bit up the canvas.

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If you have an inflammation, let's say that inflammation is happening in your nose

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well you might say : well I have a runny nose or a stuffy nose.

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Or if that inflammation is happening in your throat you might say: well I have a sore throat, might hurt.

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And if it's happening in your lungs you might have a cough.

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So one of those respiratory symptoms, remember that we've got two categories,

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All other respiratory symptoms, I'm gonna shorten it as RESP.

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Those are gonna be explained by inflammation or at least a part of inflammation.

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And remember there are also constitutional symptoms, right?

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With constitutional symptoms, those were things like having a fever or having fatigue.

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And the reason for that is that your immune system is going wild and crazy

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when you have influenza.

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It's gonna be attracted to all of those chemicals, we call these cytokines that were being released .

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And it's gonna to be attracted to the fact that you've got actual virus particles in the area,

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you know that is being infected.

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So that strong immune system is going to create some of your symptoms.

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It's actually gonna rave up your temperature.

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You'll start having a fever, chills.

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And because your energy is spent on this attack

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you're going to be fatigued.

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you're going to be fighting off the virus so you going to be fatigued,

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you might have the body aches.

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So lot of these kinds of symptoms you get as result of a strong immune response.