Flashcards in 280b hemostasis Deck (10):
1st step in hemostasis following vessel injury?
what doe endothelial cell release following injury? what is in it?
endothelin - vasoconstriction
selectins - rolling of platelets and WBCs
vWF - binds GpIb on platelets
what do WBCs release after they start rolling on endothelium due to selectins?
microparticles put tissue factor on surface --> bind platelets and activate
how are the extrinsic and intrinsic pathways connected?
TF-VIIIa activate intrinsic
extrinsic (TF-VIIa and Xa) --> small amount of X --> small amount of thrombin --> activates intrinsic pathway
intrinsic is required to form clot b/c extrensic only gets the process started
where does coagulation cascade occur?
surface of cells - WBCs rolling along have TF; platelets have other factors on surface
test for clotting? what is added? what is test tubes and blood bags to stop clotting?
intrinsic - PTT (partial thromboplastin time) - add silicates/PL
extrinsic - PT (prothrombin time) - add TF
citrate binds Ca
vitamin K - fxn
reduced form (vit K epoxide I-- warfarin) --> coenzyme for g-carboxylation of II, VII, IX, X, C, S, Z
allows Ca bridge to form b/w negative membrane PL (phosphatidylserine on platelets and macrophages)
Fibrin and FXIII
fibrinogen - triple helix of peptides -- dimer with disulfide bonded
thrombin cuts off fibrinopeptides A and B --> leave knobs that allow proper fitting b/w dimers to form a half-staggered sequence --> long aggregated polymer
cross linking via FXIII --> forms bond b/w dimers, activated by thrombin
limiting factors for blood coagulation?
Ca --> must give with blood transfusions b/c citrate is in bad which blocks Ca action --> too low of Ca to form clot