2.4 Extrinsic and Intrinsic Pathway for Initiating Clotting

• What initiates the clotting process?

  Trauma to vascular wall or blood
• What is prothrombin activator's role in clotting?

  It converts prothrombin to thrombin
• How is prothrombin activator formed?

  Through extrinsic and intrinsic pathways
• What are the two pathways for prothrombin activator formation?

  Extrinsic and intrinsic pathways
• What role do blood-clotting factors play?

  They catalyze the clotting process
• How are most clotting factors designated?

  By Roman numerals
• What indicates the activated form of a clotting factor?

  A small letter "a" after the numeral
• What begins the extrinsic pathway for clotting?

  Traumatized vascular wall or tissues
• What is released from traumatized tissue?

  Tissue factor or tissue thromboplastin
• What is the composition of tissue factor?

  Phospholipids and a lipoprotein complex
• What activates Factor X in the extrinsic pathway?

  Factor VII and tissue factor complex
• What is the role of activated Factor X (Xa)?

  It forms prothrombin activator
• What does activated Factor X combine with to form prothrombin activator?

  Tissue phospholipids and Factor V
• What happens to prothrombin in the presence of Ca++?

  It is split to form thrombin
• How does thrombin affect Factor V?

  It activates Factor V
• What is the role of activated Factor V in the clotting process?

  It accelerates prothrombin activation
• What acts as a vehicle in the prothrombin activator complex?

  Platelet phospholipids
• What is the positive feedback effect of thrombin?

  It accelerates the entire clotting process
• What is the second mechanism for initiating clotting?

  Intrinsic pathway for initiating clotting
• What triggers the intrinsic pathway for clotting?

  Trauma to blood or exposure to collagen
• What are the steps in the intrinsic pathway for clotting?

  1. Activation of Factor XII
  2. Release of platelet phospholipids
  3. Activation of Factor XI
  4. Activation of Factor IX
  5. Activation of Factor X
  6. Formation of prothrombin activator
• What does blood trauma cause in the intrinsic pathway?

  Activation of Factor XII and platelet phospholipids
• What happens to Factor XII upon blood trauma?

  It converts into activated Factor XII
• What role do platelet phospholipids play in clotting?

  They contain platelet factor 3 for clotting
• What is the second step in the intrinsic pathway?

  Activation of Factor XI
• What is required for the activation of Factor XI?

  High-molecular-weight kininogen and prekallikrein
• What does activated Factor XI do?

  It activates Factor IX
• How does activated Factor IX contribute to clotting?

  It activates Factor X
• What is the role of activated Factor VIII in the intrinsic pathway?

  It helps activate Factor X
• What condition is associated with a deficiency of Factor VIII?

  Classic hemophilia
• What is thrombocytopenia associated with?

  Deficiency of platelets
• What does activated Factor X combine with to form prothrombin activator?

  Factor V and phospholipids
• What initiates the cleavage of prothrombin?

  Prothrombin activator
• What is the final outcome of the intrinsic pathway?

  Formation of thrombin from prothrombin