Haematology - Haemostasis

Question 1

What three things happen after injury to result in a stable haemostatic plug?

Answer 1

• Blood vessel constriction
• Platelet aggregation
• Coagulation cascade

Question 2

How does blood vessel constriction results in a stable haemostatic plug?

Answer 2

It causes reduced blood flow

Question 3

How does platelet aggregation lead to a stable haemostatic plug?

Answer 3

• Dependent on collagen
• Uses Gl2b/3a
• Forms primary haemostatic plug
• Feeds into blood vessel constriction and coagulation cascade
• Platelet activation as a result of aggregation leads to plug

Question 4

How does the coagulation cascade result in a stable haemostatic plug?

Answer 4

• Dependent on Tissue Factor
• 3 Steps: initiation, amplification, propagation + thrombin burst
• Feeds into platelet aggregation through release of thrombin
• Fibrin formation results in plug

Question 5

Which part of the cells are anti- and pro-coagulant?

Answer 5

• Endothelial cells = anti-coagulant
• Extracellular matrix - pro-coagulant

Question 6

What forms primary haemostasis?

Answer 6

Platelet adhesion + aggregation

Question 7

What forms secondary haemostasis?

Answer 7

Coagulation cascade

Question 8

Which conditions are as a result of primary haemostasis dysfunction?

Answer 8

Bleeding disorders
- vWD
- ITP
- HIT

Question 9

Which conditions are as a result of secondary haemostasis dysfunction?

Answer 9

Coagulation disorders
- Haemophilia
- Vit K deficiency
- Liver disease

Question 10

What is the difference between platelet adhesion and platelet aggregation?

Answer 10

Platelet adhesion is when the platelet binds to the subendothelium. It uses Glp1b + vWF or Glp1a and releases ADP + thromboxane.

Platelelt aggregation is when the platelets adhere to eachother. It uses Glp2b/3a

Question 11

What does tissue factor pathway inhibitor (TFPI) inhibit?

Answer 11

Initiation of the coagulation cascade (the binding of TF to FVII)

Question 12

What does antithrombin inhibit?

Answer 12

Propagation of the coagulation cascade (FII, FIX, FX)

Question 13

What does activated protein C (APC) inhibit?

Answer 13

Propagation of the coagulation cascade (FV, FVIII)

Question 14

What is the process of the intrinsic pathway of the coagulation cascade?

Answer 14

• Surface activation (aPTT) of FXII to FXIIa (12)
• Activation of FXI to FXIa (11)
• Activation of FIX to FIXa (9)
• Activation of FVIII to FVIIIa (8)
• FVIIIa, FIXa, calcium, platelet factor + FVIIa activate FX to FXa (10)

Question 15

What is the process of the extrinsic pathway of the coagulation cascade?

Answer 15

• Tissue activation (PT) activates FVII to FVIIa (7)

Question 16

What is the final common pathway of the coagulation cascade?

Answer 16

• FXa activates FV to FVa (5)
• FXa, FVa, calcium + platelet factor activates prothrombin to thrombin (FIIa)
• Thrombin (FIIa) activates fibrinogen to fibrin (FIa)
• Fibrin + FXIIIa form a fibrin clot
• Plasminogen is activated to plasmin by tissue plasminogen activators (TPA)
• Plasmin and the fibrin clot form fibrin degradation products

Question 17

Which blood test relates to which part of the coagulatino cascade?

Answer 17

• APTT (activated partial thromboplastin time) = intrinsic pathway
• PT (prothrombin time) = extrinsic pathway
• TT (thrombin time) = common pathway

Question 18

Which blood tests are used to monitor warfarin and heparin therapy

Answer 18

Heparin = APTT
Warfarin = PT + INR