Introduction to Haemostasis Flashcards
What is haemostasis?
The arrest of bleeding and the maintenance of vascular patency
What are requirements of haemostasis?
Permanent state of readiness
Prompt response
Localised response
Protection against unwanted thrombosis
What are components of normal haemostatic systems?
Formation of platelet plug (primary haemostasis)
Formation of fibrin clot (secondary haemostasis)
Fibrinolysis
Anticoagulant defenses
How are platelets formed?
Formed in bone marrow by budding from megakaryocytes
How long do platelets live for?
7-10 days
Endothelial (vessel wall) damage exposes and does what?
Exposes collagen and releases von willebrand factor (VWF) and other proteins to which platelets have receptors -> platelet adhesion at site of injury
Then there is secretion of various chemicals from platelets that lead to aggregation of platelets at site of injury
What are causes of failure of platelet plug formation?
Vascular
Platelets - reduced number (thrombocytopenia); reduced function
Von Willebrand factor
What are consequences of failure of platelet plug formation?
Spontaneous bruising and purpura
Mucosal bleeding - epistaxis, GI, conjunctival, menorrhagia
Intracranial haemorrhage
Retinal haemorrhages
What are screening tests for primary haemostasis?
Platelet count
Describe how the formation of fibrin clot happens
What are causes of failure of fibrin clot formation?
Single clotting factor deficiency (usually hereditary e.g. haemophilia)
Multiple clotting factor deficiencies (usually acquired e.g. DIC)
Increased fibrinolysis (usually part of complex coagulopathy)
Draw out how fibrinolysis occurs
What are consequences of failure of fibrin clot formation?
No characteristic clinical syndrome
May be combined primary / secondary haemostatic failure
Pattern of bleeding depends on single or multiple abnormalities, and the clotting factors involved
What screening tests can we do for fibrin clot formation?
PT time
Activated partial thromboplastin time (APTT)
What questions are important to ask in bleeding disorders?
History - bleeding / bruising
Duration (?life -long)
Previous surgery / dental extractions
Drug history
FH
Examination
Draw how serine protease inhibitors (anti-thrombin) cause anticoagulation
Draw how protein C and protein S cause anticoagulation
