Platelet adhesion to collagen occurs
**Core Concept**
Platelet adhesion to collagen is an essential step in the formation of a hemostatic plug, which is crucial for stopping bleeding at the site of vascular injury. This process involves the interaction between platelets and the subendothelial collagen matrix, which is exposed after injury to the vascular wall. The adhesion of platelets to collagen is mediated by specific receptors on the platelet surface.
**Why the Correct Answer is Right**
The correct answer is **von Willebrand factor (VWF)**. VWF is a large, multimeric glycoprotein that plays a critical role in platelet adhesion to collagen. It acts as a bridge between platelets and the collagen matrix, facilitating the initial adhesion of platelets to the site of injury. VWF binds to both platelet glycoprotein Ib (GPIb) and collagen, enabling platelets to adhere to the injured vessel wall. This process is essential for the formation of a stable platelet plug and the subsequent steps of hemostasis.
**Why Each Wrong Option is Incorrect**
**Option A:** Glycoprotein IIb/IIIa (GPIIb/IIIa) is a platelet receptor involved in the final common pathway of platelet aggregation, but it is not directly involved in platelet adhesion to collagen.
**Option B:** Platelet factor 4 (PF4) is a platelet-derived protein that promotes platelet aggregation and the formation of a platelet plug, but it is not directly involved in platelet adhesion to collagen.
**Option C:** Fibronectin is an adhesive glycoprotein that interacts with platelets and the collagen matrix, but it is not the primary mediator of platelet adhesion to collagen.
**Clinical Pearl / High-Yield Fact**
The von Willebrand factor (VWF) is a key player in platelet adhesion to collagen, and its deficiency or dysfunction can lead to a bleeding disorder known as von Willebrand disease. This is the most common inherited bleeding disorder, characterized by easy bruising, prolonged bleeding after injury or surgery, and a tendency to develop blood clots in the small blood vessels.
**Correct Answer: A. von Willebrand factor (VWF)**