Hemostasis

Overview of Hemostasis

• Primary hemostasis involves the formation of a platelet plug (white thrombus)
• This plug is not very stable so it requires more work to stabilize the plug
• Secondary hemostasis comes to the rescue
• The end goal is for fibrinogen to be converted to fibrin which forms a stable mesh

Platelets

• Role is to initiate the stopping of bleeding
• Have a lifespan of 7-10 days
• Come from megakaryocytes
• Very small bits with no nucleus
• Have many granules
• Release agents that constrict blood vessels and that participate in clotting cascade (von Willebrand Factor)
• Clot retraction
• Help maintain healthy endothelium

Secondary Hemostasis

• Clotting factors are produced by the liver and exist in blood plasma
• Injury results in the sequential activation of clotting factors
• The extrinsic pathway is faster than the intrinsic
• Many factors require calcium and phospholipid in order to work
• Clot retraction requires the help of platelets

Problems in Hemostasis

1. Low platelet numbers
2. Impaired platelet activity
3. Congenital diseases
4. Drugs such as aspirin can be a cause
5. Aspirin inhibits thromboxane A2 (TXA2), produced by platelets and important for platelet function
6. Many people who have suffered heart attacks are continuously on aspirin

1. Congenital diseases
2. Low production of certain clotting factors
3. Acquired
4. Low vitamin K
5. Anti-coagulant drugs
6. Acquired liver disease