Haemostasis Flashcards
What does haemostasis do? [3 marks]
- Prevents tissue loss from tissue injury
- Restores vascular integrity & promotes healing
- Limits infection
What are the four key components of haemostasis? [4 marks]
- Endothelium
- Coagulation
- Platelets
- Fibrinolysis
How does the horseshoe crab maintain haemostasis? [2 marks]
- A primitive coagulation pathway is initiated for endotoxin.
- Its haemolymph contains amoebocytes which wards off infection by bordering up the infected area.
What are the stages of haemostasis? [6 marks]
- Vascular spams
- Platelet activation
- Haemostatic plug
- Coagulation
- Stable clot formation
- Clot dissolution
What makes up a blood clot? [3 marks]
- Fibrin mesh
- Platelets
- Erythrocytes
What does the vessel wall do? [3 marks]
- Inhibits coagulation
- Prevents platelet aggregation
- Provides a barrier to reactive element in the subendothelium such as collagen and TF
What happens in primary haemolysis? [3 marks]
- Vasoconstriction (immediate)
- Platelet adhesion (within seconds)
- Platelet aggregation and contraction (within minutes)
What happens in secondary haemolysis? [2 marks]
- Activation of coagulation factors tissue factor and collagen (within seconds)
- Formation of fibrin (within minutes)
What happens of fibrinolysis? [2 marks]
- Activation of fibrinolysis (within minutes)
- Lysis of the plug (within hours)
What forms does von Willebrand factor come in? [2 marks]
- Globular in the subendothelium
- Filamentous in blood (unravels)
How is vWF distributed? [2 marks]
- 95% in the constitutive path: leaves cell via vesicles in Golgi apparatus
- 5% in the regulated path: via Weibel-Palade bodies
What does thrombin do? [2 marks]
- Activates circulating platelets
- These platelets release more clotting factors.
Where does secondary haemostasis occur? [1 mark]
Negatively-charged phospholipid membrane from activated platelets
How do platelets stick to vWF? [1 mark]
Via glycoproteins on vWF
What does vWF do? [2 marks]
- Forms a bridge between collagen and platelets
- Protects FVIII from rapid clearance
Where are most clotting factors made? [1 mark]
In the liver
What does the extrinsic clotting factor involve? [3 marks]
- FVIIa-X complex formed
- FVa activates prothrombin
- Fibrogen comes out of solution to become X linked fibrin mesh
What does the intrinsic clotting factor involve? [1 mark]
Prekalikrein
What happens at the initiation of clot formation? [3 marks]
- Exposed tissue factor binds to FVIIa
- Complex binds small bits of FX and FV
- Small amount of thrombin produced
What happens at the propagation of clot formation? [2 marks]
- Activated factors enable binding of FXa and FVa to surface membranes
- Exposes the reaction sites necessary
- Thrombin burst allows large scale production of fibrin
What converts plasminogen to plasmin? [1 mark]
Tissue plasminogen activator
What are formed when cross-linked fibrin is degraded? [1 mark]
D dimers
What are formed when non-cross-linked fibrin is degraded? [1 mark]
Fibrin degradation products
What can tissue plasminogen activator (tPA) be used for? [2 marks]
- Therapeutic thrombolysis
- Alongside streptokinase (bacterial activator)
What causes ecchymosis (easy bruising)? [2 marks]
High levels of:
- fibrinolytic factors
- anticoagulant proteins
What causes chronic venous insufficiency (clotting)? [2 marks]
High levels of:
- coagulation factors
- platelets
