 Hi, you guys. So today's topic is blood and capillary exchange. And I just had a somewhat traumatizing experience of going to search for a nice image of blood on the internet. And it was pretty much horrifying. I don't know if it's because I'm particularly sensitive today or it's close to Halloween or I got nothing. I did find a happy place after being in like a, oh god, I think I want to vomit place. I got out of there. This made me feel better. And today's lecture is actually a really cool one because in talking about blood, we're going to do this like transitional link between where we've been with everything that we've done so far in human physiology to where we're going with, I mean we're like halfway through and this will take us to the rest of the story. To start out the conversation, we really need to think about what blood is and when we think about the structure of blood that will, I'm sure this shocks you, will shed light on the functions that we're going to look at. I mean, we haven't ever not talked about blood and we won't ever stop talking about blood no matter what system we're talking about because it is the substance that connects body systems. There's no question that the nervous system sends out neurons and those neurons can travel long distances to link distant anatomical structures to each other, but blood does all the rest of the linking and let's remind ourselves of what blood is made out of. So you can push pause and go through this process because you already know this stuff. What is it? 92% three liters of your blood is plasma and 92% of that is water. So plasma is basically just the fluid that your blood cells float in. The other, what two liters are cells. So you, what is it, 160 kilometer? Seriously, 160 kilogram dude has five liters of blood. Yeah, or 160 kilometer dude. I mean, he probably has five liters of blood too. What kind of cells do we have in our blood? Well, hopefully you're like, dude, you got red blood cells and when I went to my happy place of histology to make me feel better after my crazy search, red blood cells are those little pink things that you see all over. We also have white blood cells. White blood cells, when we think about their function, that's going to lead us to another big function of blood cells or blood tissue. We have platelets and these are also considered cellular elements even though platelets are actually full blown cells or like little cell fragments. Red blood cells are all about gas exchange. So they're carrying oxygen and carbon dioxide and delivering and exchanging those gases with the rest of the cells like everybody. Your cells have to be like within point, a tenth of a millimeter away from a blood supply or they'll die and that's because red blood cells, I mean, even if we allow them to starve, like you can last longer while starving than you can without having oxygen or getting rid of your carbon dioxide. So the red blood cells facilitate this gas exchange. We've got two whole lectures on respiratory system and gas exchange coming at us soon. The white blood cells, they facilitate immunity, which is another big job of the blood. The blood is, because it's going everywhere and because it has these rock and white blood cells, it's going to help us keep bad guys out and distinguish between self and non-self. The immune system is what's coming next. So we have two lectures up next on the immune system to spend time looking at the functions of those white blood cells. And then the platelets are another formed element. They're little cell fragments that are involved in clotting. And I'm going to tell you right now that clotting is called hemo-blood stasis. Keep it together, keep it together, man. Keep your blood in your blood vessels. We just were talking about cardiovascular system, blood pressure. Blood pressure, the purpose of platelets really is to prevent blood loss, which if you lose your blood, you're going to lose your blood pressure. Losing blood pressure indicates that you're not going to be able to have enough perfusion and that's like exchange at the cellular level. Okay, so that right there tells us where we're going today. We're going to talk about capillary exchange. We're going to talk about the pressure qualities involved in that. We're going to talk about clotting and how we stop the bleeding, which thank goodness we do. And then we're going to do this little intro link to the immune system. And we're going to talk about blood typing, which is an immune topic, but we're going to introduce that today to create that link. What do you feel? All right, we're going to start out by looking at the structure of capillaries because that is where exchange of anything at all, that's where it's going to take place.