Coagulation

Blood Clotting and Hemostasis

• The centerpiece of a blood clot is a platelet plug.
• Heparin is produced by mast cells and basophils to enhance the activity of antithrombin III.
• Coumadin (warfarin) inhibits the production of clotting factors in the liver by blocking vitamin K.
• Tissue plasminogen activator (tPA) is the activator that leads to the conversion of plasminogen to plasmin.
• Deficiencies in either platelets or coagulation factors lead to bleeding disorders.

Hypercoagulability

• Cancer is not a predisposing factor to hypercoagulability.
• Vitamin K deficiency leads to impaired clotting factor synthesis.

Clotting System Regulation

• The clotting system has internal checks and balances to prevent excessive clotting.

Hemostasis Disorders

• Petechiae, platelet dysfunction, and low platelets are associated with thrombocytopenia.
• Liver disease causes impaired clotting factor synthesis and platelet dysfunction.
• A deficiency in clotting factors results in bleeding disorders.
• Hemophilia A is a genetic disease that leads to clotting factor deficiency.

Blood Tests

• The whole blood clotting time (WBCT) measures the time it takes for blood to clot in a glass test tube.
• The prothrombin time (PT) measures the time needed for recalcified citrated plasma to clot in the presence of tissue thromboplastin.
• Platelet function tests assess platelet aggregation and secretion.

Platelet Activation

• Thromboxane A2 (TXA2) leads to vasoconstriction after an injury.
• The intrinsic pathway is activated when the Hageman factor contacts subendothelial substances exposed by vascular injury.
• ADP stimulates platelet activation and secretion.
• Factor VIII is the carrier for factor VIII in circulation.

Vitamin K and Clotting Factors

• Vitamin K is required for the synthesis of clotting factors II, VII, IX, and X in the liver.

Homeostasis

• The purpose of homeostasis is to maintain a balance between bleeding and clotting.

Anticoagulant Therapy

• The normal range for INR (international normalized ratio) for those on anticoagulant therapy such as warfarin is 2-3.
• Platelets release granules containing ADP, calcium, and serotonin during the activation process.