BMS201 || L13 Quiz

Blood Physiology: Key Concepts and Facts

• Thrombomodulin binds with thrombin, forming a complex that activates protein C, functioning as a natural anticoagulant.
• Thrombin is adsorbed to fibrin threads, with an estimated 85-90% of thrombin preventing excessive clot spread.
• Heparin, primarily sourced from mast cells, enhances its anticoagulant action when combined with antithrombin III.
• Plasmin, derived from plasminogen, is responsible for digesting fibrin threads in the fibrinolytic system.
• Tissue plasminogen activator (t-PA) is mainly released from injured tissues and vascular endothelium.
• Thrombin is not classified as a plasminogen activator; others include urokinase and streptokinase.
• The t-PA inhibitor primarily delays fibrinolysis, regulating the breakdown of clots.
• Hemophilia A results from a deficiency in factor VIII, leading to excessive bleeding.
• Disseminated Intravascular Coagulation (DIC) is characterized by both excessive bleeding and intravascular clotting.

Endothelial Effects on Clotting

• A smooth endothelial surface helps prevent blood clotting by inhibiting the intrinsic clotting system's activation.
• The glycocalyx layer on endothelium repels clotting factors and platelets, thereby preventing clot formation.
• Damage to the endothelial wall activates both factor XII and platelets, initiating the intrinsic clotting mechanism.

Antithrombin III and Regulation of Clotting

• Antithrombin III inactivates remaining thrombin not adsorbed to fibrin, playing a critical role in blood clot regulation.
• The effectiveness of antithrombin III increases significantly when it combines with heparin, enhancing thrombin removal.
• The heparin-antithrombin complex also removes activated coagulation factors including factors II, VII, and IX.

Plasmin System and Fibrinolysis

• The conversion of plasminogen to plasmin is triggered by the release of t-PA from injured tissues, crucial for clot breakdown.
• Urokinase's primary role involves preventing clot formation specifically within the urinary tract.
• Medical conditions such as acute myocardial infarction can benefit from fibrinolysis through t-PA, streptokinase, or urokinase administration.

Thrombocytopenia and Purpura

• Thrombocytopenic purpura occurs when the platelet count falls below 50,000/mm³.
• Non-thrombocytopenic purpura arises from decreased functioning platelets or defects in the vessel wall rather than platelet count reduction.
• Hemophilia A represents 85% of hemophilia cases and is classified as a sex-linked recessive disease.

Thromboembolism and DIC Triggers

• Thrombo-embolic conditions can occur due to very slow blood flow and rough endothelial surfaces.
• DIC may be triggered by severe medical situations like septic shock, retaining a dead fetus in the uterus, or repeated blood transfusions.