If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:8:53

Video transcript

okay so let's say that this is a red blood cell so what makes out what makes up the outer layer this red blood cell well since it's a cell it has a cell membrane and that's made up of lipids but embedded in those lipids there's all kinds of proteins and molecules some of which I'm drawing here that have all kinds of different functions but there are two of them that are sort of more important than the others at least for this topic that we're going to talk about and those are the a molecule and the B molecule so I think you'll be pretty happy with those names not too hard to remember and I'm actually calling the molecules and not proteins because they're actually not proteins they are actually something called glycol lipids which I actually didn't realize at first glycolipids glyco meaning a sugar group lipid meaning like a fat group so it's like some kind of mix of a sugar and fat you can look it up if you're interested but what's interesting is that not all people have both of these molecules these glycol lipids on their red blood cells some people do have both but some have only one so for example some people might have only the a or as you can imagine some people would have only the B and some people can you figure out the last possibility some people have neither a nor B and of course all these people have all kinds of other proteins and molecules imbedded in their red blood cells now the reason why we care about this and why I'm talking about these A's and these B's is that in medicine we often have to give blood transfusions so let's say you got in a car accident and you lost a lot of blood you're rushed to the hospital and if you've lost enough blood they'll give you a transfusion of blood transfusion just means they'll put a needle in your vein and pump blood into your veins but it turns out that you can't just give any blood to anyone and it has to do with these a and B groups and so for example it turns out and we'll we'll explain this but for example it turns out that if you are the kind of person who has this kind of blood that only has a x' on your blood cells then it turns out that you can't get a blood transfusion from someone who has this kind of blood a s and B's and so let's learn why so if you remember from the immune system there's something called an antibody and we usually draw it in this shape here so if you remember from the immune system your body has something called antibodies and it uses these antibodies to fight things that it doesn't want in the body so for example if you have a bacterium I'm drawing one here you'll have an antibody that will bind to that bacterium and the purpose of that is that now your body knows that it should destroy this bacterium so this antibody is kind of like a tag that marks this guy for destruction but your body is very careful not to make antibodies against itself which is obvious right because if your body made antibodies against itself then it would start to attack itself so for that reason someone who has this kind of blood which means that all of their red blood cells have A's and B's on them that person would not want to make antibodies against the a and the B molecule because if they did then their body would attack all of their red blood cells so these people don't have these antibodies but let's say if you have this kind of blood then you might not make an antibody against the a molecule but you can make it against the B molecule because the B is not in your body and so there's no risk that your body is going to pack itself by making an antibody against the B molecule so these guys don't have the a antibody but they do have the B antibody these guys on the other hand they can have the a antibody but they don't want to be antibody because then they would attack themselves whereas this final guy can you guess what he has so he can actually have both a and B antibodies and he actually will have both because that's the way your immune system works it makes antibodies against pretty much anything that is not you that is not yourself and a and B molecules are not part of this guy he has none of them so he'll make antibodies against them so now let me ask you what would happen if this guy someone with just a blood type A blood got in a car accident and needed a transfusion let's say they rushed to the hospital and you give them blood from someone with a and B molecules well what would happen is that this guy's antibodies against B would go and bind to the B molecules on the blood that he's just received and then his body would start to destroy all of these cells that he just received and that's bad because first of all it's a waste you gave this guy blood and now he's just going to destroy it but second of all it's going to cause a huge amount of inflammation because this guy's body is going to suddenly see all these antigens that he thinks are really dangerous and it's going to cause his whole immune system to rev up and that will actually be bad for him so let's go through all the different possible transfusions between these different kinds of people let's go through them methodically by drawing a table so on one side of the table will have the donors so bear with me as I draw this table out we'll have a B donor a donor type B donor and you know we call this kind of blood we can't call it Type B or type A because that's these guys so we actually call this o Type O and then we also have the same guys as possible recipients so we have type a B blood recipient type blood recipient type B blood recipient and Type O blood recipient and let's make this into a table okay so here are our donors blood donors and here are our blood recipients so what did we say before we said that someone with type A blood cannot receive blood from someone with type A B blood so that means that a recipient with a B donor is no good well how about someone with a B blood can they receive blood from someone with a B blood and the answer is yes because the guy with a v blood has no antibodies against a or b so he won't attack the a v blood that is given to him so why don't you pause the video for a moment and try to fill in the rest of this table okay so hopefully you've paused for a second and tried to fill in the rest of the table and now we'll fill it in together so someone with a B blood can receive blood from a he can receive blood from B and he can receive blood from O because he has no antibodies to any to either A or B so he won't react to any of these guys now likewise someone with type A blood can of course receive from a B can receive from B oh can receive from O but B cannot receive from a B nor can O nor can be received from a nor can O nor can oversee from B nor can a receive from B but o and give to everyone so something interesting you'll notice here is as we just said o can give to anyone because the Oh blood type has no A's or B's on it so no one's going to react to it so for that reason we call oh the universal donor and the other interesting thing you'll notice is that a bee can receive from everyone so for that reason we call him the universal recipient and all these things by the way a bee a bee oh these are blood types so when someone asks you for your blood type this is what they're referring to and this is why it's really important to know your blood type if you're ever going to require a blood transfusion