Platelet adhesion to collagen is mediated by which of the following
**Core Concept**
Platelet adhesion to collagen is a crucial step in the formation of a hemostatic plug, where platelets interact with the damaged vascular wall. This process is mediated by specific receptors on the platelet surface that bind to collagen in the subendothelial tissue.
**Why the Correct Answer is Right**
The correct answer is von Willebrand factor (VWF). VWF is a large, multimeric protein that is secreted by endothelial cells and stored in the Weibel-Palade bodies. When a blood vessel is injured, VWF is released and binds to the exposed collagen in the subendothelial tissue, forming a "platelet bridge" that anchors platelets to the site of injury. This process is essential for the initiation of platelet aggregation and the formation of a stable hemostatic plug. VWF also binds to the platelet surface receptor, glycoprotein Ib (GPIb), which is necessary for platelet adhesion to collagen.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically relate to platelet adhesion to collagen. While platelet-activating factor (PAF) is involved in platelet activation and aggregation, it is not directly involved in platelet adhesion to collagen.
**Option B:** This option is incorrect because fibrinogen is primarily involved in platelet aggregation, not adhesion. Fibrinogen binds to the platelet surface receptor, glycoprotein IIb/IIIa (GPIIb/IIIa), and forms a bridge between platelets, leading to platelet aggregation.
**Option C:** This option is incorrect because thrombin is involved in the coagulation cascade and the formation of a fibrin clot, but it is not directly involved in platelet adhesion to collagen.
**Clinical Pearl / High-Yield Fact**
The von Willebrand factor (VWF) is a critical protein for platelet adhesion to collagen, and its deficiency or dysfunction can lead to bleeding disorders such as von Willebrand disease. VWF also plays a role in platelet adhesion to other surfaces, such as vascular endothelium and damaged tissue.
**Correct Answer: B. Fibrinogen**