Activated by coagulation factor XIIa, plasma kallikrein (KLKB1) cleaves high molecular weight kininogen (HK) to release bradykinin, the potent vasodilator peptide. The resulting HKa is a multi-function protein consisting of a heavy chain with three cystatin-like domains and a light chain with two domains, one of which is also known as kininostatin. KLKB1 can also activate factor XII and plasminogen/PLG, and the latter can also be activated by u- or t-Plasminogen Activator (PA). Plasmin degrades fibrin, initiating fibrinolysis. PAs and plasmin are inhibited by serpin E1 and F2, respectively. Interaction of uPA and uPAR leads to a variety of consequences.