Blood Coagulation MCQ - Practice Questions with Answers

 Blood coagulation 

• Whenever some injury occurs to any part of the body, it starts bleeding 
• Blood coagulation or blood clotting refers to the process of formation of a blood clot to prevent bleeding
• The process of blood coagulation involves a cascade of reactions and these are carried out by clotting factors
• Thirteen clotting factors have been identified and these are as follows :

• The cascade reactions can be divided into three major steps :

Step I Formation of prothrombinase

• At the site of injury, the blood platelets disintegrate and release a phospholipid, called platelets factor -3 ( platelet thromboplastin)
• Injured tissues also release a lipoprotein called thromboplastin. 
• These two factors combine with Ca ions and certain proteins of the blood plasma to form an enzyme called prothrombinase

Step II Catalyzation of prothrombin into thrombin

• The prothrombinase inactivates heparin (anti-coagulant) in the presence of calcium
• Enzyme prothrombinase catalyzes the breakdown prothrombin (inactive plasma protein) into an active protein called thrombin 
• Prothrombin is factor II. It is glycoproteinaceous and synthesised in the liver by vitamin K

Step III Conversion of fibrinogen into fibrin and formation of a clot

• Thrombin acts an enzyme and brings about depolymerization of fibrinogen ( a soluble plasma protein) into its monomers
• Later thrombin stimulates repolymerization of these monomers into long insoluble fibre-like polymers called fibrin
• Fibrins form a dense network upon the wound and trap blood cells resulting in a clot. 
• The blood clot seals the wound and thus the bleeding stops.
• Vitamin K is essential for clotting as it is required for the synthesis of prothrombin in the liver.