Intro/Blood Clotting

Introduction & Blood Coagulation

In order to understand how Hemophilia A affects the blood, one must first understand how the blood clots. When someone is usually cut or injured, all you see is the blood…but then minutes later there is a scab. Here, I will try to explain this event and how a hemophiliac's blood fails in the clotting process.

Every bleeding injury begins at the blood vessel. When a blood vessel is injured, platelets will form around the site. Platelets are disc-shaped structures that travel in your blood in order to help your blood clot. The platelets act as a temporary plug to stop further bleeding. However, this platelet plug is too disorganized to act as a long-term solution. Therefore, a final fibrin-based plug needs to be tightly woven onto the injured spot. To achieve this final plug, a series of chemical reactions must occur; this includes the use of the clotting factors. This series of chemical reactions is often referred to as the clotting cascade. The clotting cascade uses amplification to form the proper sized fibrin clot with the small amount of molecules activated by the injury. Amplification is the process which uses the released amount of molecules that in turn activates a series of chemical reactions that determines the correct size for the clot.

This image is from the National Hemophilia Foundation, http://www.hemophilia.org, displaying the four main steps to blood clotting. As you can see, hemophilia lacks in step 4, where the incompletion of a fibrin clot causes prolonged bleeding.

The clotting cascade is where we see the effects of hemophilia. Patients with Hemophilia A have a limited, absent, or mutated clotting factor VIII. Due to this abnormality, the blood is unable to clot or takes an extended amount of time to do so.

Sources for this page:

• Wilson, Jennifer F., MS. "Hemophilia." Gale Encyclopedia of Medicine . Ed. Jacqueline L. Longe. 3rd ed. Detroit : Thomson Gale, 2006. Science Resource Center . Thomson Gale. 28 November 2006