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Spin down your blood and find out what it's made up of. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
Video transcript
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.