Vitamin K dependent coagulation factors include
**Core Concept**
Vitamin K-dependent coagulation factors are essential for the normal coagulation cascade, with a crucial role in blood clot formation. These factors are synthesized in the liver and require vitamin K as a cofactor for their post-translational modification, which involves gamma-carboxylation of glutamic acid residues.
**Why the Correct Answer is Right**
The correct answer, B. IX and X, highlights the importance of vitamin K-dependent factors in coagulation. Factor IX (Christmas factor) and factor X (Stuart-Prower factor) are both crucial for the intrinsic and extrinsic pathways of coagulation. Factor IX is activated to factor IXa by factor XIa, while factor X is activated to factor Xa by both the intrinsic and extrinsic pathways. The gamma-carboxylation of these factors by vitamin K-dependent carboxylase is essential for their binding to phospholipid surfaces, facilitating the coagulation cascade.
**Why Each Wrong Option is Incorrect**
**Option A:** Factors II and III are not vitamin K-dependent. Factor II (prothrombin) is activated to thrombin by factor Xa, but it does not require vitamin K for its synthesis. Factor III, also known as tissue factor, is not a coagulation factor and does not participate in the coagulation cascade in the same way as the other factors.
**Option C:** Factor III is not a vitamin K-dependent coagulation factor, as mentioned earlier. Factor V, on the other hand, is a vitamin K-independent coagulation factor that serves as a cofactor for the activation of prothrombin to thrombin.
**Option D:** Factor VIII is a vitamin K-independent coagulation factor that serves as a cofactor for the activation of factor X to factor Xa. Factor XII is also a vitamin K-independent coagulation factor that initiates the intrinsic pathway of coagulation.
**Clinical Pearl / High-Yield Fact**
Vitamin K-dependent coagulation factors are essential for the normal coagulation cascade, and deficiencies in these factors can lead to bleeding disorders such as hemophilia A and B.
**✓ Correct Answer: B. IX and X**