Describe the process of blood clotting.

Explanation

Clotting of blood :
(1) When the blood vessel is intact, blood does not clot due to the presence of active anticoagulants like heparin and antithrombin.
(2) But when there is an injury causing rupture of a blood vessel, bleeding starts.
(3) This bleeding is stopped by the process of blood clotting during which liquid blood is converted into semisolid jelly.
(4) The events occurring during blood clotting are as follows :
(i) Release of thromboplastin from thrombocytes and injured tissue.
(ii) Formation of enzyme prothrombinase in the blood due to initiation of thromboplastin.
(iii) Conversion of inactive prothrombin into active thrombin by prothrombinase in the presence of Ca ions.
(iv) Conversion soluble fibrinogen into insoluble fibrin by thrombin.
(v) Formation of a clot by enmeshing platelets, other blood cells and plasma in the fibrin fibres enmesh.
(5) These reactions occur in 2 to 8 minutes. The refore, clotting time is said to be 2 to 8 minutes.