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Intrinsic and Extrinsic Pathway of Coagulation | Hematology👨‍⚕️

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▬▬▬▬▬▬▬▬▬▬ Contents of this video ▬▬▬▬▬▬▬▬▬▬
00:00:00 Definition Of Coagulation
00:00:55 Difference Between Extrinsic And Intrinsic Pathways
00:03:49 Intrinsic Pathway
00:05:10 Extrinsic Pathway
00:07:16 Experiment
00:08:12 When Injury Happens
00:10:11 Mechanism Of Intrinsic Pathway
00:16:55 Mechanism Of Extrinsic Pathway
00:19:12 Platelet Aggregation

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The intrinsic pathway is activated through exposed endothelial collagen, and the extrinsic pathway is activated through tissue factor released by endothelial cells after external damage. Intrinsic Pathway. This pathway is the longer pathway of secondary hemostasis.

Intrinsic Pathway

This pathway is the longer pathway of secondary hemostasis. It begins with the activation of Factor XII (a zymogen, inactivated serine protease) which becomes Factor XIIA (activated serine protease) after exposure to endothelial collagen. Endothelial collagen is only exposed when endothelial damage occurs. Factor XIIA acts as a catalyst to activate factor XI to Factor XIA. Factor XIA then goes on to activate factor IX to factor IXA. Factor IXA goes on to serve as a catalyst for turning factor X into factor Xa. This is known as a cascade. When each factor is activated, it goes on to activate many more factors in the next steps. As you move further down the cascade, the concentration of that factor increases in the blood. For example, the concentration of factor IX is more than that of factor XI. When factor II is activated by either intrinsic or extrinsic pathway, it can reinforce the intrinsic pathway by giving positive feedback to factors V, VII, VIII, XI, XIII. This makes factor XII less critical; patients can actually clot well without factor XII. The intrinsic pathway is clinically measured as the partial thromboplastin time (PTT).

Extrinsic Pathway

The extrinsic pathway is the shorter pathway of secondary hemostasis. Once the damage to the vessel is done, the endothelial cells release tissue factor which goes on to activate factor VII to factor VIIa. Factor VIIa goes on to activate factor X into factor Xa. This is the point where both extrinsic and intrinsic pathways become one. The extrinsic pathway is clinically measured as the prothrombin time (PT)
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