 Okay, so let's talk about red blood cells and how you know that your red blood cells are yours or how you know that maybe they're not yours. And blood type is based on certain proteins that are embedded in the red blood cell. Now, you have a sense. I mean, the whole purpose of the immune system is to determine what's me and what's not me. And if it's not me, let's kill it right now. Thankfully, you know, from a, like if we don't think about our immune system, if we think about just like us, it's pretty easy to tell what's me and what's not me. Like that's me, that's me, this is my hand, that's my nose. Like I can tell that it's mine. And it's pretty easy to look at someone over across the room and be like, yeah, that isn't me. And then on that hand, like, no, that hand is not mine. Your body can tell which cells are you and which cells are not you based on the markers that are found in the cell membrane. And there are like holy crazy number of markers. Like there might be a marker that looks like this in your own cell membrane. And then there might be a marker that looks like this in your own cell membrane. And there's like a bajillion different markers that your body recognizes, dog pound, that's me. You're my homie. You've got the markers that tell me that it's all cool. And then if somebody comes in with a marker, that's like, dude, who brought that crazy thing in here. If a cell comes in like any cell, a red blood cell, a joe cell, like any random cell that has a different marker, your body is super quick and it better be quick to go, whew, intruder, not me. These things, whether they're in you or they're on something else, a bacteria, a virus, a piece of pollen, a grain of pollen. It's about to say a grain of sand, but I'm pretty sure a grain of sand doesn't initiate an immune response. Anything that initiates an immune response is called an antigen. Now this might be kind of weird. An antigen can initiate an immune response. And again, why would we have an immune response? Dude, the thing we're responding to isn't us. Kill it. Get rid of it. So these things are antigens, even when they're in us. These are my antigens. That's my red blood cell. Those are my antigens. And my body knows that, dude, they could initiate an immune response, but when they're in me, my body's like, dude, I got you. You're part of me and I will not initiate an immune response against you. However, that one, that's not me. I don't recognize it. Call it. Are you cool with the idea of an antigen? Red blood cells have special antigens. They can have special antigens. They can have A antigens or B antigens. And depending on the antigens, the red blood cell has embedded in its cell membrane. That tells you what blood type you are. So this person right here is AB blood, has AB blood. Somebody with O type O blood, tell them what they're going to look like. Go ahead, take a wild guess. Whoa, that's a dark little red blood cell. Dogs, O means nada. No antigens embedded in the cell membrane of the red blood cell that has type O blood. Now, I say no antigens. That's the biggest pile of doodoo that I've ever heard in my life. No A antigens or B antigens. There's all sorts of antigens embedded in all of your cells to help you identify as you. And to help you communicate with things. And of course, we've got receptors. There's all sorts of stuff going on. If you had type A blood, you're just going to have the A antigens. Type B blood, you're just going to have the B antigens. Now, that's just half the story. That's awesome. Antigens, great. The other half of the story is that also floating in your blood plasma, you have antibodies. And antibodies are these awesome little proteins. They contribute to the concentration of plasma proteins. So they contribute to osmotic pressure in your blood. And they help tag bad guys. So antibodies, they all have a very similar structure. They all have this like Y shaped structure. And they have a short chain and a long chain. And at the end, so it kind of looks like it's a little Y. And at the end of an antibody, they have these variable regions. So the rest of this Y shaped antibody is the same as everybody else's. So all antibodies are the same except for this variable region. And you can see that that antibody that I just drew, go ahead and take a wild guess. Who do you think that that antibody is going to actually connect to? I don't think that it goes down that far. See me just fixing that. Oh, look, my other one is a little circle and it's green. Look, can you tell who they're going to bind to? This antibody on the right is an anti-A antibody. Does that work for you? Because look, it's going to bind to the A antigen. You can see that it's a little A antigen. And here's the deal. If the antibody matches the antigen, done. Game over. You're like the whole point of an antibody matching with an antibody, the cell that has the antigen on it or the whatever it is, the pollen grain or whatever, that has the antigen on it. So antibody over here with the blue variable region matches my little blue B antigen. So this is an anti-B antibody. Now, take a wild guess. If I have AB blood, do you think I have anti-Bs, anti-As, or both in your plasma? You have no antibodies, no A, anti-A, or anti-B antibodies. You've got a bajillion antibodies. Because, whoa, if you had antibodies, anti-As, or anti-Bs, you would attack your own red blood cells. You cool? How about type O blood? What kind of antibodies are found in the plasma of someone with type O blood? You're going to have both anti-As and anti-Bs. And you can see from this that if someone with type O blood were to receive blood cells from someone with AB blood, they would have the antibodies and they would attack the blood cells and you would end up with basically mashed potato blood that isn't going to pump very well through your system. So that's a sad story. You don't want that to happen. What else do I need to tell you about this? I think that's it. I think that's all you need to know. And the whole point is we've now been introduced to antibodies and we've been introduced to the idea of antigens. Let's talk about Rh factor because the Rh factor is another antigen that may or may not be found embedded in your red blood cell. And again, we're just kind of getting kind of an intro into the concepts associated with the immune system. I'll be right back to do Rh.