8. Hemostasis And Thrombosis

Question 1

Normal hemostasis

Answer 1

Involving platelets clotting factious and endothelium

Occurs at vascular site of injury

Results in the formation of a blood clot

Balance between coagulation and bleeding

Question 2

Blood clotting mechanism

Answer 2

Release of clotting factors from both injured tissue cells and sticky platelets at the injury site - form temporary platelet plug

Series of chemical reactions that eventually result in the formation of thrombin

Formation of fibrin and trapping blood cells to form a clot

Question 3

Coagulation cascade

Answer 3

Series of amplifying enzymatic reactions that leads to the deposition of insolvable fibrin clot

Question 4

Clinical significances of coagulation cascade

Answer 4

Prothrombin time (PT) assay assesses the function of the proteins in the extrinsic pathway (factors VII, X, V, II and fibrinogen)

INR (international normalized ratio)

The partial thromboplastin time (PTT/aPTT) assay - screens function of the proteins in the intrinsic pathway (factors XII, XI, IX, VIII, X, V, II and fibrinogen)

Thrombin time (TT) - measures final step in coagulation

Question 5

PT - prolonged

aPTT - normal

Answer 5

Factor VII deficiency (extrinsic) - decreased coagulation factors - prolonged PT

Liver disease - major organ that makes coagulation

Warfarin administration - PT prolonged

Question 6

PT - normal

aPTT - Prolonged

Answer 6

Deficiency of factors VIII, IX, XI

Heparin administration

Question 7

PT - prolonged

aPTT - prolonged

Answer 7

Deficiency of prothrombin, fibrinogen, or factors V or X - common pathway

DIC

Question 8

Thrombin activities

Answer 8

Conversion of fibrinogen to fibrin (mesh that traps platelets)

Platelets activation

Pro-inflammatory effects

Anti-coagulation effects - molecular switch when prothrombin binds thrombomodulin

Question 9

Antithrombotic properties of endothelium

Answer 9

Non active = anti-coagulation effects

Platelet inhibitory effects: shield platelets from vWF and collagen - capture platelets

Anticoagulant effects - thrombomodulin binds thrombin, endothelial protein C receptor binds to protein C - inactivated clotting factors

Fibroniolytic Effects - synthesizing t-PA (tissue plasminogen activator) involved in anticoagiulation, lysis fibrin

Question 10

Blood vessel damage, blood clot and clot dissolution

Answer 10

1. Subendothelial exposure
2. Adhesion
3. Activation of platelets
4. Aggregation of platelets
5. Platelet plug formation
6. Clot retraction and dissolution