Haemostasis Flashcards
what is haemostasis?
the arrest of bleeding and the maintenance of vascular patency
what is primary haemostasis?
formation of a platelet plug
what is secondary haemostasis?
formation of the fibrin clot
when does fibrinolysis occur?
when haemostasis is secure
where are platelets formed and how?
bone marrow
budding off from megakaryocytes
what is the average life span of a platelet?
7-10 days
what do platelets bind to in damaged endothelium?
collagen
what is a reduced number of platelets called?
thrombocytopenia
what is a common cause of reduced platelet function?
taking anti-platelet medications
how can problems with primary haemostasis present?
spontaneous bruising
mucosal bleeding
retinal haemorrhages
what is the screening test to assess primary haemostasis?
platelet count - part of a FBC
what does TF/VIIa do?
activates V/XA
what does V/Xa do?
converts prothrombin to thrombin
what does thrombin do?
converts fibrinogen to fibrin
activates VIII/IXa
what does VIII/IXa do?
activates V/Xa
what are the two possible groups of causes of a problem with secondary haemostasis?
single clotting factor deficiencies
multiple clotting factor deficiencies
name a cause of a single clotting factor deficiency
haemophilia
what clotting factor is deficient in haemophilia A?
VIII
what clotting factor is deficient in haemophilia B?
IX
name a potential cause of a multiple clotting factor deficiency
DIC
what is fibrinolysis?
the breakdown of the fibrin clot
what breaks down fibrin?
plasmin
what is the plasmin precursor?
plasminogen
what converts plasminogen to plasmin?
tissue plasminogen activator (TPA)
what is the breakdown product of fibrin?
fibrin degradation products (FDPs)
what are cross-linked FDPs called?
D-dimers
what are the two screening tests for secondary haemostasis?
prothrombin time (PT) activated partial thromboplastin time (APTT)
what test measures the intrinsic pathway in secondary haemostasis?
PT
what test measures the extrinsic pathway in secondary haemostasis?
APTT
name three naturally occurring anticoagulants
anti thrombin
protein C
protein S
what is thrombophilia?
a deficiency of naturally occurring anticoagulants
what does thrombophilia increase the risk of?
venous thrombosis
what is the role of VWF?
helps hold platelets to each other and to collagen
what clotting factor may be deficient if there is an isolated prolonged PT?
factor VII
what coagulation screen result should be monitored when on warfarin?
INR - based on PT
what coagulation screen result should be observed when on heparin?
APTT
