Haemostasis Flashcards
What are the four main components of haemostasis?
Formation of platelet plug –> primary haemostasis
Formation of platelet plug –> secondary haemostasis
Fibrinolysis
Anticoagulant defences
Describe the process of primary haemostasis
Endothelial (vessel wall) damage exposes collagen and releases Von Willebrand Factor (vWF) + other proteins
–> platelet adhesion at sight of injury
The secretion of chemical from platelets –> aggregation of platelets at sight of injury
What are the causes of failure of platelet plug formation?
Vascular Platelets: - reduced number (thrombocytopenia) - reduced function Von Willebrand Factor deficiency
What are the consequences of failed platelet plug formation?
Spontaneous bruising + purpura Mucosal bleeding - epistaxis, GI, conjunctival, menorrhagia Intracranial haemorrhage Retinal haemorrhages
What is the screening test for problems with primary haemostasis?
Platelet count
Formation of the fibrin clot is also known as what?
The coagulation cascade (secondary haemostasis)
Which factors are involved in the extrinsic pathway?
Tissue factor (TF) + factor 7
Which factors are involved in the intrinsic pathway?
Factors 12, 11, 9 + 8
Describe the common pathway?
Factor X (10) + factor V (5) –>
Prothrombin (factor 2) –> Thrombin (factor 2a)
Fibrinogen –> Fibrin
How does thrombin perform ‘amplification’ of the coagulation cascade?
Thrombin activates intrinsic pathway (factors 11 + 8)
Which test identifies a problem with the intrinsic pathway?
activated partial thromboplastin time (APTT)
Which test identifies a problem with the extrinsic pathway?
Prothrombin time (PT)
What are the causes of failed fibrin clot formation?
Single factor deficiency e.g. Haemophilia Multiple factor deficiency e.g. DIC Increased fibrinolysis (complex coagulopathy)
Describe the process of fibrinolysis
Tissue plasminogen factor (tPA) cleaves plasminogen to plasmin
Plasmin breaks fibrin down to FDPs (fibrin degradation products)
Which naturally occurring anticoagulants act on the extrinsic pathway?
Tissue factor pathway inhibitor
