This example says that hemophilias and thrombophilias are both classes of dangerous blood clotting disorders. If blood does not clot properly, it's referred to as hemophilia. If blood clots too easily, it's referred to as thrombophilia. We previously compared positive feedback mechanisms to a fire. Explain how thrombophilia and hemophilia relate to the analogy of positive feedback as a fire.

Alright. So remember our analogy of positive feedback as a fire. You start a fire, the heat from the fire catches more things on fire. As more things catch on fire, it gets hotter. As it gets hotter, it catches more things on fire. As more things catch on fire, it gets hotter, so on and so on. And then, we have down here this picture of the woods that are totally on fire. We have a huge forest fire, completely out of control. And over here, we have this wood that looks kind of wet; it's not really burning. It looks like maybe someone tried to get it going, but they can't get a fire going.

Let's compare these to hemophilia and thrombophilia. Let's start with hemophilia. Of the forest out of control fire or the wet wood that doesn't really get going, which one do you think sounds more similar to hemophilia in terms of our analogy? Well, to me, hemophilia sounds like this wet wood. And that's because, in hemophilia, the blood doesn't clot properly. That clot never starts. It's sort of like you never have that on switch for the positive feedback loop. You just can't get the fire going. You can't get the blood clotting properly. And hemophilia is a very dangerous condition, where people who have it can bleed to death very easily, even just from a small cut.

In contrast, that leaves the forest fire probably more like thrombophilia. I'm going to write that out. And as I write it, think why. Well, a forest fire is a positive feedback loop totally out of control. It started maybe just with a little spark. That spark caught some dry tinder going, but everything's so dry that pretty soon the entire forest is going. Well, that's, in an analogy, sounds kind of like thrombophilia. Your blood clots too easily. It starts even maybe when there isn't even a cut, and it starts to clot. Those clots can be very dangerous because a blood clot where it's not supposed to be can lodge and block blood flow in the wrong place in the body. That can be very dangerous. So a forest fire, in terms of our analogy, sounds a lot more like thrombophilia.

With that, there are some practice problems below. And like always, I'll see you in the next video.