Past Papers · SAQ
Haemostasis — Fibrinolysis & Alteplase
2024A Q06
Exam question(a) Outline the process of fibrinolysis including how it interacts with the coagulation system (80% of marks). (b) Describe the mechanism of action and adverse effects of alteplase (20% of marks).
CICMWrecks answer
Master answer
Fibrinolysis
- Process by which fibrin clot is degraded to prevent excessive clot formation
- Plasminogen incorporated into clot
- Injured tissues and vascular endothelium gradually produce Tissue Plasminogen Activator (t-PA) in a delayed manner.
- Urokinase is produced by monocytes, macrophages and urinary epithelium
- Factor XII (Hageman factor) acts as a weak activator of plasminogen
- Plasminogen activated by t-PA, u-PA and factor XII to plasmin, a serine protease
- Plasmin cleaves fibrin into fibrin degradation products → reducing clot stability → Clot breakdown
Regulation of fibrinolysis
- Plasmin Activator Inhibitor (PAI) 1 & 2 – produced by vascular endothelium and inhibits tPA and uPA
- Protein C inactivates PAI, TAFI
- Thrombomodulin – expressed on in tact endothelium – binds thrombin and subsequently activates protein C
- Thrombin Activatable Fibrinolysis Inhibitor – produced by liver and cleaves plasmin binding sites on fibrin → decreased degradation
- α2 anti-plasmin – produced by liver, inhibits circulating plasmin, not fibrin bound plasmin
Sakurai 2016
Past papers
Exam appearances
| Exam | Exact exam wording | Candidate success |
|---|---|---|
| 2024A Q06 | (a) Outline the process of fibrinolysis including how it interacts with the coagulation system (80% of marks). (b) Describe the mechanism of action and adverse effects of alteplase (20% of marks). | 3% |