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Haemostasis and Clotting Quiz
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Which of the following best describes a key physiological role of von Willebrand factor that explains the bleeding tendency seen in von Willebrand disease?
- A Transport of factor V in the circulation You picked ✕
- B Activation of plasminogen leading to fibrinolysis You picked ✕
- C Conversion of fibrinogen into fibrin to stabilise the clot You picked ✕
- D Direct activation of thrombin during the coagulation cascade You picked ✕
- E Stabilisation of factor VIII and promotion of platelet adhesion You picked ✓
Correct!
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The answer is E: Stabilisation of factor VIII and promotion of platelet adhesion
Explanation
Why E is correct
See Platelets. Option E is correct because von Willebrand factor (VWF) has two linked jobs. At a damaged vessel wall it binds exposed collagen and helps platelets attach to it through receptors on their surface, which starts the platelet plug. In the circulation it also carries factor VIII, a clotting protein, and protects it from being cleared too early. When VWF is low or abnormal, as in von Willebrand disease, the platelet plug forms poorly and factor VIII levels can fall as well. The bleeding is typically from skin and mucous membranes, such as frequent nosebleeds, easy bruising and heavy periods, and more severe disease can cause bleeding into joints or the gut. A memory aid: VWF is the glue and the chaperone, gluing platelets to the wall and chaperoning factor VIII through the blood.
- Platelet job: von Willebrand factor binds exposed collagen and helps platelets attach to the damaged vessel wall
- Carrier job: it carries factor VIII in the blood and protects it from being cleared too early
- Deficiency: in von Willebrand disease the platelet plug forms poorly and factor VIII levels can fall
- Typical bleeding: from skin and mucous membranes, such as nosebleeds, easy bruising and heavy periods
Why the other options are incorrect
- A. Transport of factor V in the circulation: Von Willebrand factor carries factor VIII, not factor V, so this is not a role that explains the bleeding tendency in von Willebrand disease. Your answer
- B. Activation of plasminogen leading to fibrinolysis: Plasminogen activators form plasmin, which digests fibrin and breaks up clots. This is a separate clot-removal pathway that does not involve von Willebrand factor. Your answer
- C. Conversion of fibrinogen into fibrin to stabilise the clot: Thrombin converts fibrinogen to fibrin, and von Willebrand factor is not the enzyme that does this. It would be the answer if the question asked about the last step of the clotting cascade. Your answer
- D. Direct activation of thrombin during the coagulation cascade: Thrombin is made from prothrombin by upstream clotting reactions, not by von Willebrand factor. This protein supports platelet sticking and carries factor VIII. Your answer
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1
Which enzyme is primarily responsible for breaking down fibrin during clot removal?
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2
A 12-year-old boy has recurrent knee swelling after minor trauma and prolonged bleeding following venepuncture. His maternal uncle had similar bleeding problems. His activated partial thromboplastin time (APTT) is prolonged, while his prothrombin time (PT) and platelet count are normal. Which abnormality most likely explains this presentation?
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