Home We KNOW the earth is at least 6,000 yrs old Proof of a young earth A Series of Eyes Irreducible Complexity The Cilium Blood Clotting The Professional Literature Detection of Design A Complicated World Curiouser and Curiouser Videos Links Contact Us   Blood Clotting Now let's talk about a different biochemical system of blood clotting. Amusingly, the way in which the blood clotting system works is reminiscent of a Rube Goldberg machine. The name of Rube Goldberg; the great cartoonist who entertained America with his silly machines, lives on in our culture, but the man himself has pretty much faded from view. Here's a typical example of his humor. In this cartoon Goldberg imagined a system where water from a drain-pipe fills a flask, causing a cork with attached needle to rise and puncture a paper cup containing beer, which sprinkles on a bird. The intoxicated bird falls onto a spring, bounces up to a platform, and pulls a string thinking it's a worm. The string triggers a cannon which frightens a dog. The dog flips over, and his rapid breathing raises and lowers a scratcher over a mosquito bite, causing no embarrassment while talking to a lady. When you think about it for a moment you realize that the Rube Goldberg machine is irreducibly complex. It is a single system which is composed of several interacting parts, and where the removal of any one of the parts causes the system to break down. If the dog is missing the machine doesn't work; if the needle hasn't been put on the cork, the whole system is useless. It turns out that we all have Rube Goldberg in our blood. Here's a picture of a cell trapped in a clot. The meshwork is formed from a protein called fibrin. But what controls blood clotting? Why does blood clot when you cut yourself, but not at other times when a clot would cause a stroke or heart attack? Here's a diagram of what's called the blood clotting cascade. Let's go through just some of the reactions of clotting. When an animal is cut a protein called Hageman factor sticks to the surface of cells near the wound. Bound Hageman factor is then cleaved by a protein called HMK to yield activated Hageman factor. Immediately the activated Hageman factor converts another protein, called prekallikrein, to its active form, kallikrein. Kallikrein helps HMK speed up the conversion of more Hageman factor to its active form. Activated Hageman factor and HMK then together transform another protein, called PTA, to its active form. Activated PTA in turn, together with the activated form of another protein (discussed below) called convertin, switch a protein called Christmas factor to its active form. Activated Christmas factor, together with antihemophilic factor (which is itself activated by thrombin in a manner similar to that of proaccelerin) changes Stuart factor to its active form. Stuart factor,working with accelerin, converts prothrombin to thrombin. Finally thrombin cuts fibrinogen to give fibrin, which aggregates with other fibrin molecules to form the meshwork clot you saw in the last picture. Blood clotting requires extreme precision. When a pressurized blood circulation system is punctured, a clot must form quickly or the animal will bleed to death. On the other hand, if blood congeals at the wrong time or place, then the clot may block circulation as it does in heart attacks and strokes. Furthermore, a clot has to stop bleeding all along the length of the cut, sealing it completely. Yet blood clotting must be confined to the cut or the entire blood system of the animal might solidify, killing it. Consequently, clotting requires this enormously complex system so that the clot forms only when and only where it is required. Blood clotting is the ultimate Rube Goldberg machine.