**Core Concept**
The major in vivo pathway of coagulation refers to the physiological process by which blood clots form to prevent excessive bleeding following vascular injury. This pathway involves a complex interplay of coagulation factors, platelets, and endothelial cells.

**Why the Correct Answer is Right**
The intrinsic and extrinsic pathways converge at the common pathway, leading to the formation of thrombin, which then converts fibrinogen to fibrin, resulting in clot formation. The major in vivo pathway of coagulation is primarily regulated by the tissue factor pathway, initiated by the exposure of tissue factor to blood following vascular injury. This pathway is crucial for maintaining hemostasis and preventing excessive bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it refers to the extrinsic pathway, which is one of the two pathways that converge at the common pathway but is not the major in vivo pathway.
**Option B:** This option is incorrect as it refers to the intrinsic pathway, which is another pathway that converges at the common pathway but is not the major in vivo pathway.
**Option C:** This option is incorrect as it refers to the contact activation pathway, which is a minor pathway involved in the initiation of coagulation.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the major in vivo pathway of coagulation is primarily regulated by the tissue factor pathway, and any defects in this pathway can lead to bleeding disorders such as hemophilia.

**Correct Answer:** D.