Blood Clotting: Mechanisms and Stages | Free Biology Notes

Blood Clotting: Mechanisms and Stages

In this article we will discuss about the blood clotting and their Mechanism

  • When an injury or trauma is caused, the wound does not continue to bleed for a long time.
  • The blood stops flowing after sometime due to blood coagulation or blood clotting.
  • This is a mechanism to prevent excessive loss of blood from the body.
  • Inside an intact blood vessel, blood does not coagulate due to the presence of active anticoagulants, heparin and antithrombins.
  • Procoagulants also occur in the blood but are in an inactive state.
  • As soon as a blood vessel is ruptured, the injured area invites formation of a clot.

Mechanism of blood clotting

  • Enzyme cascade theory proposed by Macfarlane & Co-workers.
  • According to this theory there are 3 steps in blood clotting.

1. Releasing of thromboplastin

  • Injured tissue and platelets synthesize thromboplastin
  • These thromboplastin react with plasma proteins in the presence of Ca++ ions to form Prothrombinase enzymes.
  • This enzyme inactivate heparin. (Anti-heparin)

2. Conversion of prothrombin into thrombin

  • Prothrombinase enzyme convert inactive prothrombin into active thrombin in the presence of ca++ ion.

3. Conversion of fibrinogen into fibrin

  • Thrombin acts as enzyme and convert fibrinogen (a soluble plasma protein) into long insoluble fibre like polymers called fibrin.
  • Network of fibrin on cut or wound in which blood corpuscles got trapped. This form clotting of blood.
  • After clotting a pale yellow liquid oozes from clot called serum.

Blood Clotting Mechanisms and Stages


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