Blood coagulation-Blood Clot

Physiology of blood coagulation.
General Physiology

1. Blood Coagulation General Physiology WinnerzKlub

2. General Mechanism: Clotting takes place in 3 essential steps: In response to rupture of vessel/damage to blood itself, a complex cascade of chemical rxns occurs in the blood-net result; formation of Prothrombin Activator. Prothrombin activator catalyzes conversion of prothrombin into thrombin. The thrombin acts as an enzyme to convert fibrinogen into fibrin-fibers that enmesh platelets, blood cells, & plasma to form the clot.

3. Prothrombin to Trombin First, prothrombin activator is formed as a result of rupture of a blood vessel or as a result of damage to special substances in the blood. Second, prothrombin activator in the presence of sufficient amounts of ionic Ca++, causes conversion of Prothrombin into Thrombin. Third, thrombin causes polymerization of fibrinogen molecules into fibrin fibers. NB: The rate-limiting factor in causing blood coagulation is usually the formation of prothrombin activator & not the subsequent rxns beyond that point.

4. Prothrombin Is a plasma protein formed continually by the liver. An unstable protein that can split easily into smaller compounds, one of which is thrombin. Vitamin K is required by the liver for normal activation of prothrombin, as well as a few other clotting factors. Therefore, either lack of Vit K or the presence of liver disease that prevents normal prothrombin formation can results in bleeding.

5. Thrombin Action On Fibrinogen: Thrombin is a protein enzyme with weak proteolytic capabilities that acts on fibrinogen to form multiple fibrin monomer (s) that has ability to polymerize with other fibrin monomer molecules to form fibrin fibers.

6. {cont’d} Thrombin also activates the Fibrin-Stabilizing-Factor (a substance present in small amounts in normal plasma globulins also from platelets entrapped in the clot). Fibrin Stabilizing Factor then acts as an enzyme to cause covalent bonds btw more & more of the fibrin monomer molecules, thus adding strength to the 3-D fibrin meshwork.

7. Blood Clot: The clot is composed of a meshwork of fibrin fibers running in all directions & entrapping blood cells, platelets, & plasma. The fibrin fibers also adhere to damaged surfaces of blood vessels; therefore, the blood clot becomes adherent to any vascular opening & thereby prevents further blood loss.

8. Clot Retration -Serum After clot is formed, it begins to contract & expresses most of the fluid from the clot within 20-60mins. The fluid expressed is Serum-all its fibrinogen & most of the other clotting factors have been removed. (plasma vs. serum) NB: Platelets are necessary for clot retraction to occur.

9. Positive Feedback-Clot Formation Once a critical amount of thrombin is formed, a positive feedback kicks in that causes still more blood clotting & more & more thrombin to be formed. Thrombin has a PROTEOLYTIC ACTION that allows it to act on many of the other blood-clotting factors in addition to fibrinogen. Has a direct proteolytic effect on prothrombin itself, tending to convert this into still more thrombin.

10. THE END Sources: Tortora , 15 th Ed. Guyton and Hall, Medical Physiology. 12 th Ed.