 Tracic. Hey everybody, Dr. L. Hemostasis or the cessation of bleeding or blood clotting is a very complicated process, but I'm just going to teach you the 10,000 foot view here and the real basics. So I don't want to get bogged down in the details here. So let's start. It's a three-step process. So as you can see at the top of the page here, there's an injury that damages a blood vessel. So you've got blood and blood contents pouring out into the area. So the response, the first response is going to be vascular spasm. The first thing that happens is the smooth muscles at both edges of this wound are going to violently contract as hard as they can. And this can last for 30 minutes, maybe up to an hour. But this vascular spasm, its job is to reduce blood loss. We're looking at temporary solutions until we get to a more permanent one. So the first step is just vascular spasm to reduce blood loss. The second step is less temporary, but still not permanent. And that's going to be the formation of a platelet plug. So platelets are going to run into this area and they're going to see the damage. And plits are going to start to get real sticky and they get real spiked appearance and they get real sticky. And they're going to start to stick to one another. And they're going to start to stick to the collagen and the connect tissue in the area. And they're going to form this platelet plug. So the plug's going to clump together. It's going to attach to the endothelial lining and it's going to try to keep blood from pouring out of this opening. So that's going to be this temporary platelet plug. It can actually seal a small enough blood vessel, it can seal on its own, but this is still just buying your body time for the actual coagulation process. So I'll show you some of the details here on the next slide. But the coagulation process is a very complicated process, but it ends with the production of fibrin and that's the key. Fibrinogen is the plasma protein, but fibrinogen is water soluble, it dissolves in water. It becomes fibrin which is insoluble in water and that's what's going to form the actual clot. So just remember that. And then the conversion of fibrinogen into fibrin is what causes a blood clot to form. So those are the three steps. Let's go ahead and look at the actual blood clotting cascade. This is an example of, first of all, cascade. Whenever I hear that word, I think of snowball rolling down a hill, picking up steam. Blood clotting is an example of positive feedback because each of the clotting factors that are involved here, and there are 12, is going to actually cause the production of even more clotting factors. So it's a very complex process. Just remember that it is a positive feedback process. You see here on the top, we have the intrinsic and extrinsic pathways. Extrinsic pathways is actually caused by the external trauma or started by the external trauma. Intrinsic pathway, the damage to the blood vessel wall itself will trigger the intrinsic pathway and they both merge at what's called the common pathway. So there are 12 clotting factors. We won't go through them line by line, but I'll show you them in just a moment. Each of the clotting factors are going to be produced by the liver. The other key thing to note here is that one of the clotting factors is actually calcium. That would be clotting factor 4, but then many of them are dependent on vitamin K. So let's go ahead and look at them here. You'll see any of them that have an asterisk next to them by the source there is a vitamin K dependent one. So hopefully as you've learned in nutrition classes, vitamin K is very important in the blood clotting process. So we have fibrinogen, which actually becomes fibrin and forms the clot. We don't even go through all of them here, but you'll note that clotting factor 4 is actually calcium. Notice that we don't use clotting factor 6 anymore. They used to think that clotting factors 5 and 6 were different. They now know they're the same thing. So we leave it there as a blank. So clotting factor 5 is one, but clotting factor 6 is not. Next page, you see even more of them that are vitamin K dependent coming from the liver. So as you see, the most of the clotting factors do come from the liver. That's why people that can't produce enough clotting factors usually have this genetic issue there in their liver. The rest of these, I don't think they're very important to name the meat as far as where they go. I'm never going to ask you to know the pathways. Just wanted you to note that most of them do come from the liver and many of them are dependent on vitamin K. Okay. So that is the blood clotting system, blood clotting cascade. I hope this helps. Have a wonderful day. Be blessed.