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Blood Clotting

       Clotting of blood is also called coagulation of blood. When a person gets injured, blood starts to flow out of the injury. But, after sometime blood solidifies at the site of injury and thus prevents the excessive loss of blood from the body. This is called clotting of blood. Clotting of blood is a complex process which takes place as described below :

       When blood starts to flow out of injured tissue, a substance called thromboplastin is released by the blood platelets. The thromboplastin in the presence of calcium acts on a protein present in blood plasma called prothrombin and coverts it into thrombin. The thrombin in turn acts on a soluble protein present in plasma called fibrinogen and converts it to fibrin. Fibrin forms a network of elongated thread like fibres in which red blood corpuscles get entangled and give it a solid appearance called blood clot.

       It should be noted that blood does not solidify inside the non-injured blood vessels because blood has a substance heparin which prevents it from clotting.

Test Your Understanding and Answer These Questions:

  1. What is clotting of blood?

  2. Write a note on mechanism of blood clotting.

  3. Why blood does not clot inside a blood vessel without injury?