Editing Normal coagulation


== Three processes halt bleeding: ==

* Gap-plugging by platelets
** Platelets bind to collagen (found in exposed vessel wall) and aggregate
* Vasoconstriction
** Occurs due to serotonin and other vasoconstrictors, which come from platelets adherent to the walls of the damaged vessel
* Coagulation cascade
** The loose aggregation of platelets is bound together and converted into the definitive clot by fibrin, through a cascade of reactions
** The fundamental reaction is conversion of the soluble plasma protein fibrinogen to insoluble fibrin, catalysed by thrombin
** Thrombin is itself formed by the action of activated factor X
** Factor X can be activated by either intrinsic or extrinsic systems
*** Intrinsic pathway involves factors XII, XI, IX, and VIII
*** Extrinsic pathway involves factor VII being activated by tissue thromboplastin
** Stabilisation of the clot into a dense aggregate requires activated factor XIII and calcium ions


== Fibrinolysis ==

* Tissue plasminogen activator (t-PA) is released from endothelial cells, a process stimulated by fibrin formation. T-PA converts plasminogen to plasmin
* Plasmin causes fibrin dissolution
* Fibrinolytic agents such as streptokinase (that binds and activates plasminogen) active the fibrinolytic system
** Also tenecteplase and reteplase

[[Category:Haematology]]