Haemostasis - Bleeding: Disorders of Primary Haemostasis Flashcards
What is haemostasis?
the cellular and biochemical processes that enables both the specific and regulated cessation of bleeding in response to vascular injury
What is haemostasis for?
Prevention of blood loss from intact vessels
Arrest bleeding from injured vessels
enable tissue repair
Briefly outline the process of haemostasis.
vessel constriction > primary haemostasis > secondary haemostasis > fibrinolysis
What is involved in primary haemostasis?
formation of an unstable platelet plug (platelet adhesion/aggregation)
What is involved in secondary haemostasis?
stabilisation of the plug with fibrin (blood coagulation)
What is involved in fibrinolysis?
vessel repair + dissolution of clot (cell migration/proliferation)
Why do we need to understand haemostatic mechanisms?
diagnose/treat bleeding disorders, control bleeding, identify risk factors for thrombosis, treat thrombotic disorders, monitor drugs used for treatment
Normal haemostasis is a balance between?
bleeding vs thrombosis
fibrinolytic factors, anticoagulant proteins vs platelets, coagulant factors
What are two reasons why haemostatic balance is tipped towards bleeding?
lack of specific factor (production failure, increased clearance) or defective fx of specific factor (genetic or acquired)
In what two ways does platelet adhesion occur?
indirectly via VWF + GIpIb or directly to collagen via GIpIa
The release of what factors causes platelet aggregation?
release of ADP and thromboxane
What factors are involved in platelet aggregation?
Ca2+
fibrinogen
What is low numbers of platelets called?
thrombocytopenia
Causes of low platelets?
bone marrow failure e.g. leukaemia, B12 deficiency
accelerated clearance e.g. ITP, disseminated intravascular coagulation
What does ITP stand for?
immune thrombocytopenic purpura