platelets and clot formation Flashcards
define hemostasis
stopping bleeding
describe platelets
fragmented megakeryocytes that contain chemicals to stop bleeding
no nucleus, 5-9 day life span
formation controlled by thrombopoietin
what are the 4 stages of hemostasis
vascular spasm
platelet plug formation
blood clotting
clot retraction/dissolution
describe step 1 of hemostasis: vascular spasm
damage/pain receptors→ increased vasoconstriction in arteries/arterioles to decrease blood flow and loss
caused by thromboxanes from platelets and endothelin from damaged endothelial cells
describe step 2 of hemostasis: platelet plug formation (hint: adhesion, release reaction, aggregation)
platelet adhesion: stick to collagen in damaged epithelium
platelet release reaction: they release chemicals (thromboxane, ADP, PDGF), activating more platelets (positive feedback)
platelet aggregation: forms platelet plug due to fibrinogen adhesion and platelet-platelet adhesion
describe step 3 of hemostasis: blood clotting
coagulation
clot = network of fibrin protein which traps formed elements
involves cascade mechanism
explain the cascade mechanism
factors involved cannot be constantly active or a clot will form
One product of a reaction activates the next in the pathway
Describe the cascade pathway reactions
formation of several clotting factors (VII – XII) formed by the liver, platelets, and endothelial cells
prothrombinase→+ prothrombin to thrombin
Thrombin + Ca + factor XIII converts fibrinogen to fibrin to generate clot
describe step 4 of hemostasis: clot retraction and dissolution
tissue plasminogen activator (t-PA) converts plasminogen to plasmin
plasmin dissolves fibrin
Give examples of anticoagulants and their mechanisms
warfarin (aka Coumadin)
heparin: inactivates thrombin
aspirin: inhibits thromboxane and blocks platelet synthesis
Define hemophilia A
genetic, deficient in Factor VIII
