Let's say that I go to
the doctor's office, and I hate when this happens,
but I, once in a while, have to have my blood drawn. And the reason I hate it is
that I'm kind of a chicken when it comes to getting
my blood drawn. I don't like needles. But of course, I do as I'm
told, and I get my blood drawn. I just try to distract myself
when the blood is actually filling that needle. And I usually look away,
and before I know it, it's done, right? So it's out of my
mind, and I walk out of the office pretty
happy, because now I don't have to think
about it anymore. But here's what I
want to do now is kind of follow the path that
this blood takes and think about what happens next,
after they draw the blood. So the first step
is they usually put that blood into a tube. And usually that's done
directly, actually. These days, usually
that tube is already kind of sitting and
waiting, and it's collecting blood immediately. So this is my cap for my tube. And inside my tube,
I've got blood. This is my blood
filling up this tube. And this is kind
of a special tube. And the thing to
know about this tube is that on the walls of the tube
is a chemical that basically prevents the blood
from clotting. You don't want
the blood to clot, because it's hard to do
any sort of lab work on it. And so this tube is very
special in that way. It won't actually clot. And so to make sure it's working
properly, sometimes people kind of gently shake the
tube up a little bit, just to make sure that
there's good mixing and so that the
blood doesn't clot. Now from there, the blood
goes over to the lab. So there's a machine in the
lab that takes blood from me. This is my blood. But it also takes blood
from other people, let's say a few other patients
in the hospital that day, or in the clinic. And all of our blood is
kind of labeled and put into this machine. And what the machine
does is it spins. It basically spins
really quickly. So all these tubes,
they're attached so they don't fly away. But they basically spin as well. And if all these tubes are
spinning, then what it creates is a force called the
centrifugal force. So this process is
called centrifugation. Let me write it out here. Centrifugation. And the machine is
called a centrifuge. So it's basically going to
spin really quickly, let's say, in one direction or the other. And as a result, what
happens is that the blood starts separating out. And the heavy parts
of blood kind of go to the tip of the tube. And the less dense part of blood
actually rises towards the lid. So after you've
centrifuged-- let's say you've actually gone
through this process, and you centrifuge the blood. Now you have the
same tube, but I'm going to show you kind
of an after picture. So let's say this was before
I actually spun the tube, and now I've got an after. This is my after picture. So after I spin the tube,
what does it look like? Let me draw the tube. And the biggest
key difference here is that instead of
having one similar looking homogeneous liquid, like
we had before, now it actually starts looking really different. You've got three
different layers, in fact. I'm going to draw all
three layers for you. So this is the first layer. And this is the most
impressive layer. The largest volume
of our blood is going to be in this top layer. So remember, this is
the least dense, right? It's not very dense, and that's
why it stayed near the lid. And it's actually going
to make up about 55% of our total volume. And we call it plasma. So if you've ever
heard that word plasma, now you know what it means. So if I was to take a
drop of this stuff-- let's say I took a little
drop of this plasma, and I wanted to take
a good hard look at what was in my
drop-- 90% of plasma is going to be nothing
more than water. So that's interesting, right,
because the major part of blood is plasma, and the major
part of plasma is water. So now you're seeing why it
is that we always say, well, make sure you drink
a lot of water. Make sure you're hydrated. Because a big part of your
blood itself is water. And in fact, that's true for
the rest of your body as well. But I want to stress that
it's true for blood as well. So that leaves the rest, right? We've got 90%, we
have to get to 100%. So what is 8% of this
plasma made up of? It's protein. And let me give you some
examples of this protein. So one would be, for
example, albumin. And albumin, if you're
not familiar with it, it's an important
protein in your plasma that keeps the liquid
from kind of leaking away out of the blood vessels. Another important
protein, the antibody. And this, I'm sure
you've heard of, but antibodies are basically
involved in your immune system, making sure that you
stay nice and healthy and don't get sick
with infections. And another part of the protein,
another type of protein, to kind of keep in mind,
would be fibrinogen. And this is one important
protein involved in clotting. And there are actually many
other clotting factors, we call them, as well. So I'm just going to put
clotting factors here. So these are proteins. Things like albumin,
antibody, fibrinogen, these are all proteins. Now we've still got
2% to account for. And this is going to be things
like hormones, for example. And that could be
something like insulin. We've got electrolytes. That could be
something like sodium. And we've got, also, nutrients. So nutrients, that could
be something, for example, like glucose. So these things all
make up your plasma. So a lot of the things that
we kind of think about, talk about, are
all in your plasma. including vitamins
and things like that. So now another layer we
have right below the plasma, is here in white. And if I was to kind
of zoom in on it, it would be a very, very tiny
part of blood-- less than 1%. And this is actually
white blood cells. This layer contains white
blood cells and platelets. So these are cellular
parts of our blood. And they make up
a very tiny bit, but they're a very important
part of our blood, of course. Below this layer, so now the
most dense layer of blood, would be the red blood cells. So this is this last bit. And this, just to make it
add up, would be about 45%. And these red blood
cells, of course, contain within them hemoglobin. So sometimes it gets
tricky because you forget, you think, oh, protein,
so that must be plasma. Remember, red blood cells
and white blood cells, within them, they
have proteins as well. So just remember, they
contain lots of protein as well, within them. So, for example, hemoglobin. So this is an example, right? Now one word you may
have heard of is serum. So what is serum, exactly? Well, serum, this word,
is very, very similar to plasma in terms
of what it's made of. In fact, if I was to
circle what is in serum, I would circle this bit. Basically everything within
my blue line would be circled. This is serum. And so the only thing
I've left out of serum is fibrinogen and
the clotting factors. So plasma and serum you can just
remember being very similar. And the exception is
that the serum does not include the fibrinogen
and clotting factors. Now, looking down at the
red blood cells, what can we learn from that? Well, you may have heard
this term hematocrit. And if this was my
blood, if I actually had drawn my blood, as
I drew in this picture, and this was my blood, my
hematocrit would have been 45%. And all that means is hematocrit
equals volume taken up by red blood cells divided
by the total volume. So if, in this case,
my total volume is 100, my percent, I already
told you, is 45%. So that's why I knew
my hematocrit was 45%. It's just the percent taken
up by your red blood cells. And that's an important
percent to know, because the red blood cells
are the part of blood that are actually carrying
the oxygen around. Now to kind of stress this point
of hematocrit further and maybe even kind of introduce
a couple of new words, let me draw out three
little vials of blood. So let's say I have three
vials here-- one, two, three. And these are going to be three
different people, let's say. But they're all very similar,
same age, same gender. Because hematocrit,
what is normal, is actually going to change
depending on whether you're talking about a certain
age, a certain gender, even depending on where you
live in terms of altitude. Because let's say you live
at the top of a mountain, that is going to affect
your hematocrit as well. So a lot of things
affect hematocrit. But let's say we have
three people kind of very similar in those ways. Now the first person, I'm going
to draw out their blood here. Their plasma, let's
say, is taking up this much of their total volume. The second person, their
plasma is taking up this much of their total volume. And the third person,
their plasma is taking up, let's say, a lot, of
their total volume. Let's say all the
way down to here. So you spun all three, and
this is what you've gotten. Of course, all three still
have white blood cells. Got to draw that in. And they have
platelets, of course, that's this tiny little
layer-- less than 1%, we said. And the remainder then
has to be red blood cells. So this is the red blood
cell layer right here. This is the red
blood cell layer. And it's really large here
for this second individual. And this third
individual, it's actually kind of on the smaller side. Not too much of the volume is
taken up by red blood cells. So here, if I was to kind of go
through and label these folks, I would say, well,
this first person is what I would call normal. The second person has a
lot of red blood cells. It's so, so predominant. This is a very high
percentage, right? I know this is taking up a high
amount of the total volume. So this person has what I
would call polycythemia. It's just a medical word to say
that the volume of red blood cells over the total
volume is very high. Or you could say their
hematocrit is very high. And this person,
this third person, has a very low amount
of red blood cell volume relative to
the total volume. This is actually pretty low. And so this person, I
would say, has anemia. So if you've ever heard these
terms anemia, or I'm anemic, sometimes people say, or even
the word polycythemia, now you know it's just referring to
what volume of their blood is taken up by red blood cells.
