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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. I hate when this happens, but every once in a while, I have to have my blood drawn. The reason I hate it is that I am 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. I get my blood drawn and I try and distract myself when the blood is actually filling that needle. I usually look away, and before I know it it's done. 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 is what I want to do now, is 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. Usually that is done directly these days. Usually that tube is already sitting and waiting and is collecting blood immediately. So this is the cap for my tube. Inside my tube I've got blood. This is my blood filling up this tube. 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. So this tube is very special in that way. It won't actually clot. So to make sure it's actually working properly sometimes people gently shake the tube up a little bit just to make sure there is good mixing so the blood doesn't clot. Now from there, the blood goes over to the lab. There is a machine in the lab that takes blood from me and from other people, there are other patients in the hospital that day or in the clinic. All of our blood is labeled and put into this machine. And what this machine does is it spins. It basically spins really quickly. So all these tubes that are attached they won't fly away, but basically spin as well. 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 basically you are going to spin really quickly, lets say one direction to the other. As a result what happens is the blood starts separating out. The heavy parts go to the tip of the tube, and the less dense part of blood actually rises toward the lid. So after you centrifuge, lets say you've actually gone through this process and you've centrifuged the blood, now you have the same tube but I'm going to show you a after picture. So let's say this is 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 homogenous liquid like we had before, now it starts looking really different. You've got three different layers in fact, and 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. It's not very dense and that is why it stayed near the lid. It's actually going to make about 55% of our total volume. We call it plasma. If you have ever heard that word plasma, now you know what it means. If I was going 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 is interesting right, because the major part of blood is plasma, and the major part of plasma is water. So now you are seeing why it is that we always say "Make sure you drink a lot of water, make sure you are hydrated", because a big part of your blood itself is water. In fact that is 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've got to get to 100%. 8% of this plasma is made up of protein. Now let me give you some examples of this protein. One would be albumin. Albumin, if you are not familiar with it, is an important protein in your plasma that keeps the blood, or the liquid, from leaking out of the blood vessels. Another important protein would be antibody. This I'm sure you've heard of, but antibodies are basically involved in your immune system. Making sure you stay nice and healthy and don't get sick with infections. Another part of your protein, or another type of protein to keep in mind, would be fibrinogen. Fibrinogen. And this is one important protein involved in clotting. There are actually many other clotting factors 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 also got nutrients. Nutrients could be something like glucose. So these things all make up your plasma. So a lot of things that we think about and 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. If I was to 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 a very important part of our blood of course. But below this layer, now the most dense layer of blood would be the red blood cells. So this is this last bit, and just to make it add up, would be about 45%. And these red blood cells of course contain within them hemoglobin. Right, so sometimes it gets tricky right because you forget, you know you think "oh proteins, that must be plasma." Remember red blood cells and white blood cells within them have protein 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 were to circle what is in serum I would circle this bit. Basically everything within my blue line would be circled. This is serum. So the only thing I have 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 and the red blood cells what can we learn from that? Well, you may have heard this term hematocrit. Hematocrit. If this was my blood, if I actually had drawn my blood as I have in this picture 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 was 45%, so that is why I knew my hematocrit was 45%. It's just the percent taken up by your red blood cells. And that is an important percent to know because red blood cells are actually the part of blood that are actually carrying oxygen around. Now to stress this point of hematocrit further, and maybe introduce a couple of new words, let me draw out three little vials of blood. Lets say I have three vials, one two three. These are going to be three different people lets say. They are all very similar, same age and gender, because hematocrit what is normal is actually going to change depending on whether you are talking about a certain age, 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 who are very similar in those ways. Now the first person lets say, I'm going to draw out their blood here, their plasma lets 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, I've 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 has to be red blood cells. This is the red blood cell layer right here. It's really large here for this second individual. And this third individual it's actually on the smaller side. Not too much of the volume is taken up by red blood cells. So here, if I was going to label these folks I would say this first person is normal. The second person has a lot of red blood cells. It's so predominate. 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 I would call polycythemia. 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. 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.