- [Instructor] With red blood cells down,
white blood cells down, we're on to platelets.
Platelets really are not actually cells,
they're small fragments of a cell.
What ends up happening is,
this larger cell called a megakaryocyte
is going to allow little, tiny pieces
or fragments to break off.
It's these fragments
that are going to be called your platelets.
So we have these megakaryocytes
that allow fragments to break off to form platelets.
The platelets are really important in hemostasis,
or better known as blood clotting.
So if you need your blood to clot,
you'd better have some platelets around.
The way hemostasis works,
there's three main phases to blood-clotting.
First off, a vascular spasm,
or a constriction of blood vessels to reduce blood flow.
Actually, the spasm is going to increase blood flow
momentarily, then decrease it.
It's going to increase blood flow for a little bit,
to help get more platelets
and more clotting factors to the site.
Then it's going to help reduce the blood flow,
slow down the blood inside the blood vessel.
The platelet plug forms.
The ruptured vessel will have this makeshift plug
that's shoved into the opening,
referred to as the platelet plug.
The platelets start to attach
to the edges of the torn vessel,
and slowly work their way inward
to create a whole network or mesh covering the wounded site.
Coagulation, now once you get the platelet plug in there,
the blood vessel is pretty much sealed up,
it's not totally sealed yet.
You end up with a blood clot.
The blood clot is a series of reactions.
I mean, we're talking, I want to say, 24 or 25 steps,
not important for us.
What we're looking at is the fact
that you now have stopped the bleeding,
you've reached this coagulation phase.
Three different steps to stop bleeding,
vascular spasm, platelet plug formation,
and then coagulation.
When we're all done it should look something like this.
What you're seeing here is
the reddish capped almost structure,
those are red blood cells.
They're stuck in this, basically, formation
of fibers, red blood cells, and platelets.
This is your coagulation.
This is how your blood clots.
You form a network of platelets,
which help to trap all these fibers,
which in turn trap red blood cells,
sure, some white blood cells, too,
but by allowing all this material
to get kind of pushed up into one space,
it helps prevent a bleed-out,
helps create a clot.
Here's the pictorial view of what we're looking at.
First off, number one at the top, vessel damage.
Artery, vein, capillary, whatever.
You've damaged the blood vessel.
Number two, what ends up happening is
it'll increase a little bit,
and then shrivel down, a vascular spasm.
Less blood flow to the site momentarily.
The platelet plug will form now.
See all those blue platelets having stuffed,
or basically stuck in where the opening was.
Then you get your actual clot formation.
The platelet plug still has pores.
Fluid can still get out.
But with the particles and fibers,
nothing else is getting out.
That means now the platelets are trapping red blood cells,
the platelets are trapping strands of fibrin, or fibers,
all this trapped creates that plug
to stop bleeding completely.
Now can this work on any sized cut no matter what?
No, if it did, you wouldn't need stitches.
But only working on cuts
that have a small to moderate size
where the body can help mend itself.
Any large, gaping openings need some medical intervention.
The platelet plug cannot be big enough.
On this picture, you can see that
that red and black colored bruise
is not a typical bruise.
This is the disorder hemophilia.
Heme is blood.
Hemophilia is a genetic disorder.
That means unfortunately right from birth this occurs.
You're missing one or more clotting factors.
Remember I said, somewhere in the 20s,
well, again, don't worry about all this stuff
or anything like that,
but the fact of one missing
means this whole cascade will break down.
From this case, that bruise there
could have been a simple bump into the counter.
The problem is, with not having all the clotting factors,
the body cannot stop the bleeding as efficiently.
So in this case it looks like it probably
ruptured a blood vessel or two, maybe some capillaries,
because it could not clot,
the blood kept flowing and flowing under the skin,
creating this very large area of inflammation
and this very large area of redness.
It's hemophilia.