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血液的具体组成部分。里希(Rishi)是一名儿科传染病医生,在可汗学院工作。 Rishi Desai 创建




let's say that I go to the doctor's office and I hate when this happens but I always once in a while have to have my blood drawn and the reason I hate it is and I'm kind of a chicken when it comes to getting my blood drawn I don't like needles but I 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 and 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 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 in its collecting blood immediately so this is my cap for my tube and inside my tuba 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 also takes blood from other people let's say few other patients in the hospital that day are 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 are attached 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 and 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 kind of 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 centrifuge 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 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 kind of key difference here is that instead of having one similar looking kind of homogeneous liquid like we have 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 gonna be in this top layer so remember this is the least dense all right it's not very dense and that's why it stayed near the lid and it's actually gonna 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 and 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 in fact that's true for the rest of your body as well but but I want to stress that it's true for for blood as well so that leaves the rest right we've got ninety percent we have to get to 100 so eight percent what is eight percent of this plasma made up of its 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 blood from or the liquid from kind of leaking away out of the blood vessels another important protein would be 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 fibrinogen and this is one important protein involved in clotting and there are actually many other clotting factors we call them as well 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 gonna 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 you know 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 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% about 45% and these red blood cells of course contain within them hemoglobin right so sometimes it gets tricky because you forget you know 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 in clotting factors now looking down at the red blood cells what can we learn from that well you may have heard this term hematocrit hematocrit and if this was my blood if I actually 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 a hundred my percent I already told you was 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 were the part of blood that are actually carrying 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 gonna 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 him at a crit but let's say we have three people kind of very similar in those ways now the first person let's say there I'm gonna 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 there 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 person this first person is what I would call normal this 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 right of the total volume so this person has what I would call polycythemia polycythemia is just a a medical word to say that the volume of red blood cells over the total volume is very high or you can 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