Polite Dissent

This chart has been the bane of many a first-year med student. This is the Coagulation Cascade. It shows all the factors in the blood (in addition to platelets) that cause it to clot when an injury occurs. You’ll notice how each factor, once it becomes activated (goes from VII to VIIa, for example), acts as a catalyst for the next factor; this is why it’s called a cascade. Eventually the two pathways team up to activate factor X which activates thrombin and the “common pathway.”

As you can imagine, anyone who has a problem with one of their clotting factors is going to have a hard time coagulating their blood and forming clots. We say that these people have a bleeding disorder. For instance, a deficiency in factor VII causes Hemophilia, while a problem with factor IX causes Christmas disease (or Hemophilia B, if you prefer).

There is a flip side to this cascade — a bunch of enzymes that slow down clotting so it doesn’t get out of control. This image gives you a good idea how it works as it superimposes these molecules on the coagulation cascade. A deficiency in one of these enzymes leads to a clotting disorder — someone who is more likely than normal to form clots, including dangerous deep venous clots or pulmonary emboli.

Why do I bring all this up? Because of this scene from Deathstroke #4:

You’ll notice that there is no mention of hemoglobin in the coagulation cascade. There is a good reason for this: namely, that hemoglobin does not coagulate and is not involved in the cascade. It is inside red blood cells and while it may get caught up in blood clots, it in no way itself coagulates.

This is an example of what I call “trying to get too fancy.” If the writer had just left it at blood, as in “look at the way the blood has coagulated,” then there would be nothing wrong with the sentence. Trying to get too fancy in an attempt to make it sound more realistic actual doomed the science in this scene.