Question

Which enzyme induces lysis of fibrinogen to fibrin during fibrinolysis?
(a) Plasmin
(b) Thrombin
(c) Fibrin
(d) Trypsin

Answer 1

Hint: When the injury is caused, bleeding stops after some time due to clotting. Coagulation of blood inside the blood vessel takes place due to the presence of anticoagulant heparin and antithrombins. Plasma protein prothrombin converts soluble fibrinogen to insoluble fibrin during blood clotting.

Complete Answer:
Fibrinolysis takes place when the blood clot becomes severe due to a medical disorder and medicine. Enzyme plasmin induces lysis of fibrinogen to fibrin by which the fibrin mesh cut down from several places to fix severe clots. Tissue plasminogen activator and urokinase convert plasminogen into plasmin which synthesizes by endothelial cell, macrophage, and monocyte.

Additional information:
At the time of injury blood platelets break down and release a phospholipid called platelet thromboplastin and lipoprotein thromboplastin. Both these proteins combine with calcium ions and form enzyme prothrombinase. Prothrombinase inactivates heparin and also catalyzes the conversion of prothrombin into active protein thrombin. Thrombin acts as an enzyme and causes polymerization of fibrinogen into its monomer and then stimulates the re-polymerization of monomer into long insoluble fiber fibrin. These fibers form dense networks upon the wound to form a clot.
Clot forms in about 2-5 minutes after injury and after clotting clot starts to contract and pale yellow fluid forms which are known as serum. The serum does not consist of blood corpuscles and fibrinogen. Vitamin K helps in blood clotting by the production of prothrombin in the liver. Blood clotting is regulated by thirteen clotting factors present inside the body.

So, the correct answer is ‘Plasmin’.

Note: Hyperfibrinolysis caused by the loss of fibrinolytic inhibitor by which excess bleeding takes place. Hypofibrinolysis caused by the production of antibiotics against the plasminogen activator by which impaired clot breaks down leads to thrombosis.