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  • 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.

Let's say that I go to the doctor's office,

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