Von Willebrand's Disease is the most common in a group of diseases known as "clotting disorders" or "bleeding disorders," which are often collectively referred to as hemophilia in humans (and the term "hemophilia" is commonly used in dogs as well). In order to understand von Willebrand's Disease (vWD), it's important to have a basic understanding of how blood normally clots.
When there is an injury or other trigger for bleeding, the body responds to "plug" the bleeding source in the injury. One major component of the response is the accumulation of platelets, cellular components that physically "plug the hole." A second part of the clot formation response is a series of chemical reactions involving specific molecules known as "clotting factors," which, to think of it simply, help glue the platelets together and to the tissue/blood vessel. Those clotting factors are numbered in sequence from I to XII (1 to 12 in Roman numerals), and they follow the numbered sequence in the way they react... Factor I interacts with Factor II, and the result interacts with Factor II, etc. Obviously, with so many components involved in creating the clot that stops bleeding, the failure of any single component could severely impair the clotting process. In fact, there are a wide variety of clotting disorders, each affecting a particular step in that process. In the case of von Willebrand's Disease, there is a reduction in the concentration of a protein known as von Willebrand's Factor, which stabilizes Factor VIII and helps the clot form.
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