Anticoagulants

In 1887, Russian scientist Ivan Pavlov first postulated the existence of natural anticlotting factors in animals and humans. His extensive studies of blood circulation led him to the realization that when blood reaches the lungs, it loses some of its ability to coagulate, a process aided, he believed, by the addition of some anticlotting substance. In 1892, A. Schmidt, the father of the enzymatic theory of blood coagulation, published the first data proving the existence of coagulation-inhibiting agents in liver, spleen, and lymph node cells. He later isolated this agent from liver tissue and demonstrated its anticoagulant properties. In 1905, P. Morawitz hypothesized that thrombosis might be effectively controlled by reducing the coagulation properties of the blood using antithrombins found in plasma.

Most modern theories of coagulation are scientifically complex and involve numerous substances known as clotting factors. The major mechanism of clot formation involves the conversion of fibrinogen, a highly soluble plasma protein, into fibrin, a stringy protein. There are a number of steps in this conversion process. First, when blood vessels are severed, prothrombin activator is produced. This agent's interaction with calcium ions causes prothrombin, an alpha globulin produced by the liver, to undergo conversion to thrombin. Next, thrombin, acting as an enzyme, triggers chemical reactions in fibrinogen, binding the molecules together end to end in long threads. Once these fibrin structures are formed, they adhere to the damaged area of the blood vessel, creating a mesh that traps blood cells and platelets. The resulting sticky mass, a clot, acts as a plug to seal the vessel and prevent further blood loss.