Blood - The process of blood clotting, or hemostasis, stops blood loss - The Coagulation phase

7 important questions on Blood - The process of blood clotting, or hemostasis, stops blood loss - The Coagulation phase

What occurs in the coagulation phase?

Blood clotting; the formation of a blood clot. In the end fibrinogen (soluble protein circulating) is converted into fibrin (insoluble). As this network grows, blood cells and more platelets get trapped forming a blood clot sealing the damaged portion of the vessel.

What are the clotting factors involved? (Procoagulants)

Including Calcium ions and several proteins. Majority are proenzymes (inactive enzymes) that are converted to active enzymes to direct reactions in teh clotting response. This occurs through succesive reactions (cascade).

What pathways are involved in coagulation?

Extrinsic (outside vessel wall), intrinsic (inside vessel wall) and common (where the two pathways converge).
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What is the extrinsic pathway in coagulation??

  1. Factor III is released by endothelial cells.peripheral tissues (thromboplastin)
  2. It combines with Calcium ions and factor VII
  3. Formation of enzyme complex capable of activating factor X

What is in intrinsic pathway in coagulation?

  1. Activation of proenzymes (Factor XII) exposed to collagen fibers.
  2. PF-3, released by aggregating platelets, aids in the progress of this pathway consisting of several linked reactions.
  3. Activated VIII and IX combine to from an enzyme complex that can activate factor X

What is the relationship between the intrinsic and extrinsic pathway?

Extrinsic pathway is shorter, stimulating common pathway to produce small amounts of thrombin quickly. Intrinsic pathway reinforces the patch produced. Common pathway stimulates both pathways; thrombin stimulates the formation of tisue factors and PF-3 release.
Therefore, one large positive feedback loop.

How is blood clotting restricted? (Anti-thrombotic factors)

By substances that deactivate/remove clotting factors.
  • Anticoagulants (eg. Antithrombin-III); an enzyme that inhibits clotting factors including  thrombin
  • Heparin; released by basophils and mast cells accerlates activation of antithrombin-III
  • Thrombomodulin; released by endothelial cells that converts thrombin into an enzyme that activates protein C (this inactivates clotting facotrs and stimulates plasmin formation; breaks down fibrin strands)
  • Prostacyclin; inhibits platelet aggregation and opposes action of thrombin and ADP.

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