Pathophysiology of hemostasis

Question 1

What is the first step of hemostasis?

Answer 1

Vasoconstriction: Direct injury–>Chemical messengers from endothelial cells and platelets–>Initiation of the pain reflex

Question 2

What is the second step of hemostasis?

Answer 2

Platelet plug formation: Injury to the vascular endothelium–>VonWillebrand factor is released–>Platelets are activated by vWF–>Proteins on platelets bind with fibrinogen causing platelets to adhere

Question 3

Describe the production and lifespan of platelets

Answer 3

Produced in bone marrow and regulated by thrombopoetin. Life span is 5-10 days

Question 4

What is the third step of hemostasis?

Answer 4

(coagulation): Clotting pathway is activated by either a defect in the vessel endothelium or disruption in the vessel wall.

Question 5

What factors are important for the intrinsic pathway?

Answer 5

Hageman factor (XII), factors VIII, IX, XI and calcium

Question 6

What factors are important for the extrinsic pathway?

Answer 6

Tissue factor III, VII and calcium

Question 7

Describe the common pathway

Answer 7

starts with Factor X. Goes through prothrombin, thrombin and fibrinogen. Ends with cross linked fibrin strands. The fibrin strands glue the platelets together

Question 8

What is the purpose of fibrinolysis?

Answer 8

necessary to remove clots as the blood vessel heals

Question 9

What activates plasminogen to plasmin?

Answer 9

tissue plasminogen activator (tPA) along with factor XII and thrombin. Plasmin digests the fibrin in the clot to break it up

Question 10

What regulatory mechanisms are in place to limit clot growth?

Answer 10

Removal of clotting factors. Inhibition of activated clotting factors. Antithrombin III. Protein C inactivates V and VIII. Protein S breaks down fibrin into fibrin degradation products that act as anticoagulants. Heparin