 Hi, darlings. Today we're going to talk about blood. And you might be like, dude, we've been talking about blood. And we have, really, it seems kind of odd to me that we have an entire lecture at this point with the title, Blood, when really, pretty much for the last six lectures, we've talked about blood. I mean, even before that, we were dealing with the cardiovascular system and you can't really talk about the cardiovascular system without dealing with blood. You can't talk about blood pressure without dealing with blood. You can't talk about any kind of exchange in the, say, capillaries without talking about blood. So I kind of feel like we've had a bloody mess on our hands for quite a long time. So you might be wondering, like, really an entire lecture on blood when we've had, like, 50 of them already. This time, we're going to talk a little bit about what blood is, what it's made out of, just as a review because you've had anatomy so you know that already. But we're also going to look at one of the major jobs of blood and that is clotting. So you can imagine, it shouldn't be hard to convince you at this point that blood is actually kind of important. And if it is important, then if you are about to lose some, you should have a strategy in place to prevent massive blood loss, and that's clotting. So we're going to talk about the clotting process and then we're going to introduce the role that blood plays in the immune system. Our next two lectures are on the immune system. So, and blood really is the home of the immune system. We're going to stay in bloody land basically for the next three lectures. So let's remind ourselves before we do anything else, let's remind ourselves what is this blood you speak of. We know, right, that you have about five liters of blood in our typical, what, 160 pound fella. That's equal to about 10 and a half pints of blood. And I tell you that because if you donate blood, which I highly encourage you to do, they'll take a pint of your blood. And assuming you have the, I don't know, what the smallest size limit, I feel like it's 110 pounds that you have to be in order to donate blood in the United States. But as long as you have our way 110 pounds or whatever, the requirement is then giving up one pint of blood is not going to do you in. You just stay hydrated and don't do exercise in the next 24 hours and your body will totally adjust to that and make it happen. We already know what blood consists of. We know that blood, if we were, wow, that's kind of a wonky test tube. If we were to centrifuge blood, like take a bloody pile of blood, stick it in a test tube because I'm sure that's what you do with your bloody piles of blood, and then centrifuge it down, like spin it really fast. All the red blood cells spin to the bottom. These are your red blood cells. And dude, we've been talking about red blood cells. We know exactly what those dog pounds do. They carry our oxygen around. They actually carry some carbon dioxide too. Red blood cells are awesome. We have this little Buffy coat in the middle and the Buffy coat consists of platelets. That's what we're going to talk about today. And leukocytes are white blood cells and that's what we're going to talk about in the next two days. And then you've got all your plasma. We've talked about plasma, contains your proteins. It creates the plasma proteins, create osmotic pressure, which is what's driving a lot of fluid movements in your body. And the plasma contains other things, like antibodies, which are involved in your immune system. So let's start out with taking a closer look at our friend that I'm going to circle in green because green today is the color of, it's a good day. Those little green platelets, that's who we're going to talk about first, like what are these things and what's their job and why have we not talked about them yet. All right, platelets, let's talk about them.