Theme 3: Haematology Flashcards
what are the 5 stages of haemostats?
- vasoconstriction
- primary haemostasis
- secondary haemostasis
- clot retraction and repair
- fibrinolysis
what happens when NO production is disrupted by injury to the endothelium?
vasoconstriction
what does ADP released from damaged endothelial cells do?
ADP acts on platelet P2Y1 and P2Y12 receptors causing platelet activation- they form pseudopodia and release the contents of their granules
where is von willebrand factor found and what does it bind to in primary heamostasis?
vWF is found on exposed collagen and binds to glycoprotein 1b on platelets
what platelet glycoprotein does collagen bind directly to?
GPVI
what does cyclooxyrgenase-1 (cox-1) released by activated platelets do?
converts arachidonic acid to thromboxane A2 which activates more platelets
how do platelets bind to each other?
the GPIIb/ GPIIIa molecules on platelets bind to each other via a molecule of fibrin
what is the trigger for the extrinsic pathway of the coagulation cascade?
tissue factor
which coagulation factor is involved in the extrinsic pathway?
factor VII which then activates factor x in the common pathway
what is the trigger for the intrinsic pathway of the coagulation cascade?
negatively charged collagen in the sub-endothelium of blood vessels
which coagulation factors are involved in the intrinsic pathway?
twelve, eleven, nine, eight then ten in the common pathway
what activates factor XIII and what is its function?
thrombin (factor IIa) activates factor XIII which then stabilises the clot by cross linking fibrin
what is the function of fibrin?
fibrin forms a sticky mesh which traps platelets and RBCS into the plug stabilising it
how is plasminogen activated and what does it do?
plasminogen is activated to plasmin by tissue plasminogen activator (tPA) and urokinase.
plasmin degrades fibrin into fibrin degradation products (FDP) such as D dimer
how does sodium citrate act as an anticoagulant?
sodium citrate binds to calcium which stops the coagulation cascade. its effects can be reversed by adding calcium
which pathway does the prothrombin time measure?
the extrinsic pathway
which pathway does the activated partial thromboplastin time measure?
the intrinsic pathway
what is the INR?
the international normalised ratio is a measure derived from PT which allows standardisation of PT so it can be compared between different labs- used to measure the affects of warfarin
what is a D dimer test used for?
it is used to detect the presence of fibrin clots e.g DVT or PE
what are the different categories of platelet disorders?
quantitative- to do with platelet number e.g thrombocytopenia/ thombocytosis
qualitative- to do with platelet function. can be hereditary or aquired ( drugs, liver/renal failure)
what can cause thrombocytopenia?
decreased synthesis- BM failure, aplastic anaemia, leukaemia
increased consumption- infection, disseminated intravascular coagulation
increased destruction- idiopathic thrombocytopenia purpura (ITP), splenomegaly
how does glazmans thrombasthenia cause abnormal platelet function?
abnormality in GPIIb/IIIa (fibrinogen receptor)- platelets can’t bind to one another
how does Bernard-soulier syndrome cause abnormal platelet function?
abnormality in GPIb (vWF receptor)- platelets do not bind to the injury site
what is the pathogenesis of haemophilia A/B?
there is a genetic variant in factor VIII (A) or factor IX (B)
