Haemostasis Flashcards
Define Haemostasis
The arrest of bleeding and
the maintenance of vascular patency
Requirements of Haemostasis
Permanent state of readiness
Prompt and localised response
Protection against unwanted thrombosis
What are the components of normal haemostatic system
Formation of platelet plug
Formation of fibrin clot
Fibrinolysis
Anticoagulant Defences
What is primary haemostasis?
Formation of platelet plug
What is secondary haemostasis?
Formation of fibrin clot
Platelets are formed in the bone marrow by ‘budding’
from..
Megakaryocytes
How does platelet aggregation at site of injury work?
Endothelial damage exposes collagen and releases Von Willebrand Factor and other proteins to which platelets have receptors – platelet adhesion at the site of injury
There is then secretion of various chemicals from the platelets, which leads to aggregation
Causes of failure of platelet plug formation
Vascular
Platelets (reduced number (thrombocytopenia) and reduced function
Von Willebrand Factor
Consequences of failure of
platelet plug formation
Spontaneous Bruising and Purpura
Mucosal Bleeding
Intracranial haemorrhage
Retinal haemorrhages
Screening tests for primary
hgaemostasis
Platelet count
(No simple screening tests for other components of primary haemostasis)
Explain the formation of fibrin clots
Causes of fibrin clot formation
Single clotting factor deficiency - hereditary (haemophilia)
Multiple clotting factor - acquired (disseminated intravascular coagulation)
Increased fibrinolysis (part of complex coagulopathy)
How does fibrinolysis work?
Consequences of failure of
fibrin clot formation
No characteristic clinical syndrome
Pattern of bleeding depends on
(single/multiple abnormalities, the clotting factors involved)
Screening Tests for Fibrin Clot Formation
Prothrombin time - extrinsic working?
Activated partial thromoplastin time - intrinsic working?
