So in this lecture, we're actually going to discuss what the blood clotting cascade is and what the proteins are that are involved in this cascade. So let's begin by imagining that we're inside a blood vessel. So this is the endothelial endothelium of one side and this is the endothelium of the other side. We're essentially taking a cross section of our blood vessel. Now, this is the outside portion of the blood vessel. It's the surrounding tissue.