body, and immediately that part of the body gets a little

bit of redness, a little bit of swelling, some heat maybe,

and, of course, there'll be some pain associated with

what's going on there.

And in general, this set of symptoms that we experience,

these are known as the inflammatory response, or you

might say that there's some inflammation going on there.

And people have known about this I guess ever since really

people have been having cuts.

I think probably with modern medicine, people have been a

little bit more particular about actually classifying the

symptoms, but this isn't anything new for someone to

say that there's some type of inflammation going on or some

type of inflammatory response.

But what I want to do in this video is understand what's

causing these-- I guess we can call them macrosymptoms.

What's happening at a cellular level?

Because, really, the inflammatory response is

essentially the initial field of battle

of our immune system.

Our first line of defense is our skin or the fluids on the

outside of our skin or the mucous membranes, but the

inflammatory response is what happens when something gets

beyond that.

We get punctured with a nail, or there's some type of virus

or bacteria gets beyond our skin or the mucus that

surrounds our membranes.

This is the field of battle, especially the

initial field of battle.

So let's set up an immune battle so we can see exactly

what's going on with the inflammatory response.

And I want to be very clear.

Immunology, is still a very under understood field.

It's an area of active research.

People are still discovering the mechanisms

and it's hugely complex.

I'm sure we'll probably be studying this for a

long time to come.

So what I'm going to talk about is just the overview,

just you know the general actors and you know in general

what's causing the redness, the swelling, the

heat, and the pain.

So let me draw some skin cells.

This is a gross oversimplification of

everything, but it's really just to give an idea of what

is going on.

So I'm going to do a cross-section.

So those are some skin cells in there, and then I'm going

to-- so this is the outside world right here.

Then amongst those skin cells, I'll do some other cells.

We'll talk about what they do.

I won't go into huge detail about them.

Let's call this cell right here a mast cell.

I'll draw a few more mast cells.

Maybe another one right there.

That's a mast cell.

And if you remember from the videos on phagocytic action or

phagocytes, you'll remember there was one type called

dendritic cells and they tend to hang out near our skin.

They kind of hang out near areas that might interface

with the outside world.

I'll draw a couple of dendritic cells and these are

also the ones that were really good at

activating helper T-cells.

They're called dendritic cells.

They have no relation to the nervous system.

They just look like they have dendrites on them and that's

why they call them dendritic, but they're really phagocytes

and they tend to be near external interfaces and they

phagocytose particles and they're good at presenting

them to helper T-cells so that they can get activated and

ring the alarm bell, so to speak.

So this is just a normal, functioning, happy skin.

So that's the outside.

Over here, this is the interstitial fluid.

That's just a fancy word for the fluid that cells are kind

of being surrounded by or that bathe cells.

The cells aren't all directly connected to

the circulatory system.

The oxygen goes from the circulatory system to the

interstitial fluid and eventually finds

its way into cells.

So everything is directly connected to capillaries, but

capillaries play a big role in our circulatory system.

So let me draw that.

Instead of just drawing them as tubes, I'm actually going

to draw the cells of our circulatory system.

So let's say that this down here-- these are the

endothelial cells of our capillaries.

So these are literally the cells that make up the walls

of our capillaries.

And of course, this is a cross-section.

If I were to-- I would draw it as a tube somehow.

It's not like it's a sandwich.

It's actually a tube.

Everything is in cross-section.

So these are capillary endothelial cells, and of

course, right in here, we have our blood flowing and we'll

have red blood cells in here.

These are red blood cells.

Maybe they're flowing in that direction.

On this side, they're oxygenated.

This would be arteries and then they'd become veins as

the red blood cells lose their oxygen.

And of course, you might have circulating white blood cells

inside of your-- obviously, in much lower quantity than your

red blood cells, but just to show that they're circulating

and they're moving with your circulatory system being

pumped by the heart.

Now under normal circumstances, there is an

exchange obviously of gases between what's going on in our

circulatory system and the interstitial fluid and there's

also a mild exchange of some cells and proteins.

What we're going to see now is what happens

when we have an intruder.

So let's say someone takes a nail, dips it in some cow

manure, and then pokes you with that nail.

Let's see what happens.

So let's say someone pokes you with this nail

dipped in cow manure.

So it's got all sorts of nasty stuff on it, pathogens on it,

probably has a bunch of bacteria

sitting in the cow manure.

I didn't pick cow manure at random.

It's probably a good source of bacteria.

So as soon as it pierces the first line of defense, as soon

as it pierces your skin, a couple of things

are going to happen.

A lot of these bacteria are immediately going to start

floating around in your interstitial fluid.

The cells that it came in contact with, it pierced them.

It probably killed some cells.

It's also going to damage some of these skin cells and those

skin cells are immediately going to start releasing

chemicals, the ones that are still in a position to do so.

They're going to start releasing chemicals that are

essentially chemical messengers that move through

the-- well, at first locally in the interstitial fluid and

says, something is going on.

Something has happened to me.

And these are called chemokines.

And chemokines are just a very general word, really, for

small molecules or small proteins that cells release as

a kind of signaling mechanism.

Chemo for chemical, kine for kinetic, for moving.

These are messengers.

They move.

So these chemokines get released.

And this is all tremendously complicated.

So I'm doing very high level.

There are many, many types of chemokines.

And also you have these mast cells here, and these mast

cells can be activated by direct contact maybe with the

rusty nail.

It could be from the chemokines released by some of

these cells up here.

It could be from some of the molecules released by the

actual bacteria.

These bacteria are also releasing different byproducts

as they enter the body.

And any of the above can activate the mast cells and

mast cells release histamine.

So you can already appreciate, I'm doing a high-level

overview, and it already is kind of complicated, but I

think you get the sense of what's going on.

And if the word histamine sounds vaguely familiar, it's

probably because you've taken an antihistamine sometime

probably in the last several months,

especially during cold season.

Histamine is kind of one of the main actors in the

inflammatory response, and when you have a cold and a

runny nose and stuffy nose and all of those type of things,

those are all byproducts of the inflammatory response, and

anti-histamines essentially try to shut down that

inflammatory response so some of those symptoms disappear.

But it begs the question of is that necessarily

always a good thing?

Because, as I'm going to talk about in this video, this is

the first line of defense.

This is the first part of the battle of our immune system.

But anyway, so the histamine-- one of the things that the

histamine does is it goes to the endothelial cells that

line your capillaries, and it causes them to separate away

from each other and make the actual capillaries larger.

This is called vasodilation.

Let's say that they've all been activated with a little

bit of histamine.

The histamine has come in so now these

guys get further apart.

They get further apart and the actual

capillary becomes larger.

So this is where you get a lot of your swelling, because all

of sudden, the capillary's larger, more fluid, and

actually, it gets smaller further down so it really

encourages the fluid to collect right around here.

So this is called vasodilation, just another

fancy word for saying your

capillaries are getting dlated.

They're getting larger.

Fluid is filling them up.

Not only are things starting to collect here-- more and

more red blood cells are collecting here, obviously

there's a lot of fluid here, the white blood cells-- but

also the capillary walls are becoming more porous.

All of a sudden, things that couldn't get through them are

going to have a much easier time getting through them.

And one of those things that are going to have an easier

time getting through them-- and once again, remember, all

this other stuff is going on.

You have these histamines that are being dumped on these

endothelial cells and maybe some of it 's

getting into the serum.

You have these chemokines being released locally from

this area of damage.

You have the actual things being-- the green was the

color of the molecules being released by the viruses.

You have the chemokines, which are in blue.

They're all being released here.

And so the first responders, the phagocytes, and in

particular, the neutrophils, which are the most abundant of

the phagocytes, a subclass of white blood cells, they're

attracted to these chemicals.

They want to move in the direction that there's more of

these chemicals.

And now that the space between these capillary cells have

gotten further apart, they can get through.

So what they actually do is-- let's say that this right here

is a neutrophil.

They start kind of rolling along the wall right here.

That's called marginalization.

They roll along this wall and eventually-- so they kind of

stick to the wall.

They adhere to the wall, and then eventually they squeeze

through these gaps in the capillary wall.

This is called diapedesis or extravasation.

Sometimes it's called emigration.

These are all fancy words, but essentially it's just

squeezing through the walls.

So that's the neutrophil right there.

And then, of course, because of the vasodilation, this is

where the neutrophils will be getting dumped in and this is

exactly where they're needed.

So these neutrophils are going to be here and then they're