**3. Intrinsic pathway**

The "Intrinsic Pathway", so-called because its components are all present within whole blood, is initiated when blood comes in contact with a negatively charged surface such as glass or the surface of an activated platelet. It consists of a reaction cascade involving FXII, High Molecular Weight Kininogen (HMWK), prekallikrien, FXI, FIX, FIIa, FVIII, and Ca2+ and culminates in the activation of FX at the Common Pathway. The activated partial thromboplastin time (APTT) laboratory test measures the intrinsic pathway.
