Normal platelet adhesion depends upon which component?

Normal platelet adhesion is primarily dependent on glycoprotein Ib (GP Ib), which is a crucial receptor on the surface of platelets. This glycoprotein interacts specifically with von Willebrand factor (vWF) that is exposed at sites of vascular injury. When there is damage to the blood vessel, vWF becomes exposed and acts as a bridge between the platelets and the damaged endothelium, allowing platelets to adhere effectively to the site of injury.

The interaction between GP Ib and vWF is essential for the initial stages of hemostasis, as it facilitates the aggregation of platelets to form a stable platelet plug. This adhesion process is critical, as it is often the first step in the prevention of excessive bleeding following vascular injury.

In contrast, the other components listed play different roles in hemostasis. Fibrinogen is involved in platelet aggregation but not directly in the adhesion process. The glycoprotein IIb/IIIa complex is essential for platelet aggregation and binding fibrinogen or vWF, but it is not involved in the initial adhesion to the vessel wall. Calcium is important for many coagulation and platelet activation processes but does not specifically mediate the adhesion of platelets to the vascular surface