Von Willebrand Factor Functions
The correct answer is D (A and B) - von Willebrand factor enables platelets to adhere to collagen AND binds to and stabilizes Factor VIII. 1, 2, 3
Primary Functions of vWF
Von Willebrand factor performs two essential hemostatic functions that are well-established in the literature:
1. Platelet Adhesion to Subendothelial Matrix (Option A - Correct)
- vWF promotes platelet adhesion by anchoring platelets to the subendothelial matrix, particularly collagen. 1
- This occurs at sites of vascular injury where the endothelium is disrupted and collagen is exposed. 4
- vWF acts as a "bridge" between platelet membrane glycoproteins and subendothelial components such as collagen. 4
- This function is particularly critical under high shear stress conditions where direct platelet-collagen interaction is insufficient. 5
2. Factor VIII Carrier and Stabilization (Option B - Correct)
- vWF carries and stabilizes coagulation Factor VIII (FVIII) in circulation. 2, 3
- This carrier function is essential for normal FVIII survival in the bloodstream. 6, 7
- Without vWF, Factor VIII is rapidly degraded, leading to secondary hemophilia A-like coagulopathy. 7
3. GpIIb/IIIa Receptor Binding (Option C - Incorrect in this context)
- vWF primarily binds to GPIb (glycoprotein Ib), NOT GpIIb/IIIa, for its initial platelet adhesion function. 1, 4
- While vWF does interact with the GpIIb/IIIa receptor complex during platelet aggregation and thrombus formation under certain conditions, this is a secondary interaction. 4, 5
- The primary and most physiologically relevant platelet receptor for vWF is GPIb, which mediates the initial tethering and adhesion of platelets to the vessel wall. 1
Clinical Relevance
Understanding these functions is critical because:
- Deficiency or dysfunction of vWF results in von Willebrand disease (VWD), the most common inherited bleeding disorder affecting approximately 1% of the population. 3
- Type 3 VWD patients have virtually complete vWF deficiency and present with both mucocutaneous bleeding (from impaired platelet adhesion) and factor VIII deficiency (from loss of the carrier function). 3
- The dual function of vWF explains why VWD can present with both platelet-type bleeding and coagulation factor deficiency. 7