2.3 Fibrinogen to Fibrin (Clot Formation)

• Where is fibrinogen formed in the body?

  In the liver
• What is the molecular weight of fibrinogen?

  340,000
• What is the normal concentration range of fibrinogen in plasma?

  100 to 700 mg/dl
• How does liver disease affect fibrinogen levels?

  It decreases the concentration of fibrinogen
• Why does fibrinogen normally not leak into interstitial fluids?

  Due to its large molecular size
• What happens when capillary permeability increases pathologically?

  Fibrinogen leaks into tissue fluids
• What is thrombin?

  A protein enzyme
• What does thrombin do to fibrinogen?

  It removes peptides to form fibrin
• What is formed when thrombin acts on fibrinogen?

  Fibrin monomer
• How do fibrin monomer molecules behave after formation?

  They polymerize into fibrin fibers
• What initially holds fibrin monomer molecules together?

  Weak noncovalent hydrogen bonding
• Why is the initial clot weak?

  Fibrin fibers are not cross-linked
• What strengthens the fibrin reticulum after clot formation?

  Fibrin-stabilizing factor
• How is fibrin-stabilizing factor activated?

  By thrombin
• What does the activated fibrin-stabilizing factor do?

  Causes covalent bonds between fibrin fibers
• What is the composition of a blood clot?

  A meshwork of fibrin fibers and cells
• How do fibrin fibers interact with blood vessels?

  They adhere to damaged surfaces
• What happens to a clot within 20 to 60 minutes?

  It begins to contract and express serum
• What is serum?

  Fluid without fibrinogen and clotting factors
• Why can't serum clot?

  It lacks fibrinogen and clotting factors
• What indicates low platelet count during clot retraction?

  Failure of clot retraction
• How do platelets contribute to clot retraction?

  By activating contractile proteins
• What accelerates clot contraction?

  Thrombin and calcium ions
• What happens as the clot retracts?

  Edges of the blood vessel are pulled together
• What initiates positive feedback in clot formation?

  Development of a blood clot
• How does thrombin promote more clotting?

  By acting on other blood-clotting factors
• What effect does thrombin have on prothrombin?

  It converts prothrombin into more thrombin
• What happens when a critical amount of thrombin is formed?

  A positive feedback for clotting develops
• What is the result of the positive feedback in clot formation?

  The blood clot continues to grow
• What are the steps in the conversion of fibrinogen to fibrin?

  1. Thrombin acts on fibrinogen.
  2. Four peptides are removed.
  3. Fibrin monomer is formed.
  4. Fibrin monomers polymerize into fibrin fibers.
  5. Fibrin-stabilizing factor strengthens the fibers.
• What are the roles of platelets in clot retraction?

  • Attach to fibrin fibers
  • Release procoagulant substances
  • Activate contractile proteins
  • Contribute to clot contraction
• What are the key components of a blood clot?

  • Meshwork of fibrin fibers
  • Entrapped blood cells
  • Platelets
  • Plasma
• What is the significance of thrombin in clot formation?

  • Converts fibrinogen to fibrin
  • Activates fibrin-stabilizing factor
  • Promotes positive feedback for clotting