Respiration and Circulation — BIOLOGY STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYRespiration and Circulation5 Marks
Question
What is blood clotting? How and when does it occur?
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Answer
Blood clotting is coagulation of blood in order to stop the blood flow and resuting blood loss at the time of injury.
When the blood vessel is intact, blood does not clot due to the presence of active anticoagulants like heparin and antithrombin. But when there is an injury causing rupture of a blood vessel, bleeding starts.
This bleeding is stopped by the process of blood clotting during which liquid blood is converted into semisolid jelly.
The events occurring during blood clotting are as follows:
Release of thromboplastin from thrombocytes and injured tissue.
Formation of enzyme prothrombinase in the blood due to initiation of thromboplastin.
Conversion of inactive prothrombin into active thrombin by prothrombinase in the presence of Ca ions.
Conversion of soluble fibrinogen into insoluble fibrin by thrombin.
Formation of a clot by enmeshing platelets, other blood cells and plasma in the fibrin fibres enmesh.
These reactions occur in 2 to 8 minutes. Therefore, clotting time is said to be 2 to 8 minutes.
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