2.2 Conversion of Prothrombin to Thrombin

• What is the first step in the conversion of prothrombin to thrombin?

  Formation of prothrombin activator
• What triggers the formation of prothrombin activator?

  Rupture of a blood vessel or damage to blood
• What is required for prothrombin to convert to thrombin?

  Ionic calcium (Ca++)
• How quickly does thrombin polymerize fibrinogen into fibrin fibers?

  Within 10 to 15 seconds
• What is the rate-limiting factor in blood coagulation?

  Formation of prothrombin activator
• What role do platelets play in the conversion of prothrombin to thrombin?

  They bind prothrombin to receptors on damaged tissue
• What type of protein is prothrombin?

  Plasma protein, an α2-globulin
• What is the molecular weight of prothrombin?

  68,700
• What is the normal concentration of prothrombin in plasma?

  About 15 mg/dl
• Why is prothrombin considered an unstable protein?

  It can easily split into smaller compounds
• What is the molecular weight of thrombin?

  33,700
• How is prothrombin produced in the body?

  Continually by the liver
• What happens if the liver fails to produce prothrombin?

  Prothrombin concentration falls too low
• What vitamin is required for normal prothrombin activation?

  Vitamin K
• What can decrease prothrombin levels in the body?

  Lack of vitamin K or liver disease
• What is the consequence of low prothrombin levels?

  A bleeding tendency results