Week 12 Haematology Flashcards
(171 cards)
Describe the structure of platelets
-nucleus lacking cells (cell fragments)
-packed with granules that contain chemicals
-contains mitochondria and microtubules
-also contains many surface membrane surface receptors
function of platelets
participate in hemostasis by
forming a plug at a vessel defect
list the steps of haemostasis
vasoconstriction
primary haemostasis
coagulation
Outline an overview of hemostasis
-endothelial damage with exposed collagen fibres
-vasoconstriction
-circulating platelets (via vWF) adheres to the exposed collagen beginning the formation of platelet plug
-ADP and TXA2 are released promoting adhesion, activation and aggregation enhancing the plug
-prostacyclins and NO are released to prevent excess clotting for uninjured endothelium (confining the plug)
describe how the clot specifically forms
-prothrombin activator, activates prothrombin
-prothrombin (inactive) is converted into thrombin via vitamin K and factor 10
-thrombin converts fibrinogen into fibrin
-fibrin molecules adhere to the damaged vessel surface, forming a loose, netlike meshwork that traps blood cells,
including aggregating platelets, resulting is a clot
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role of the mechanical barrier in platelet adhesion
anticoagulant - prevents platelets from binding to suboendothelial proteins
role of anti aggregation in platelet adhesion
anticoagulant- secretes small anti aggregation molecules that prevent clotting
role of expression in platelet adhesion
anticoagulant- expresses surface anticoagulant proteins
role of fibrinolysis in platelets adhesion
anticoagulant: enables the breakdown of blood clots
role of von willebrand factor in platelet adhesion
procoagulant: vWF promotes coagulation during infections or inflammation
role of glycoprotein 1b
GP1b complex binds von Willebrand factor, allowing platelet adhesion and platelet plug formation at sites of vascular injury
list the stages of platelet plug formation
adhesion
activation
aggregation
plug
describe adhesion phase of platelet plug formation
reversible adhesion to exposed ECM; certain receptors bind to certain subendothelial factors eg vWF
describe activation phase of platelet plug formation
platelet binding to collagen triggers platelet activation,
-resulting in a conformational shape change (protrusions to increase SA),
-granule secretion
-receptor activation
describe aggregation phase of platelet plug formation
GP2b/2a on platelets bind to fibrinogen irreversibly; fibrinogen acts as a molecular glue
describe plug phase of platelet plug formation
forms a plug of degranulated platelets, trapped by fibrinogen, with entrapped blood cells
what factors trigger platelet activation
ADP
Thromboxane A2
thrombin
role of ADP in platelet activation
secreted by activated platelets, activates itself and platelets in the vicinity
role of thromboxane A2 in platelet activation
TXA2 diffused out of activated platelets, activating itself and other platelets
role of thrombin in platelet activation
formed from the coagulation cascade, enables coagulation to occur
role of GP 1a/2a and GP 6
binds to collagen -> adhesion
role of GP 1b/5/9
bind to vWF–> adhesion
role of GP 2b/3a
bind to fibrinogen–> aggregation