Flashcards in Clotting Deck (17)
First platelets adhere to the site of injury, how so?
Gp 1a/2a + 6 bind directly to exposed collagen
GP 1b bind to vWF, indirectly to collagen
GP 2b/3a bind to Fibrinogen
second thrombosis is activated in the platelets by?
Cell surface receptors (ADP, adrenaline, thrombin) activate the conversion of arachidonic acid to Thromboxane 2 by COX
Third, What causes platelets to aggregate?
After a platelet plug is formed, we then form a fibrin clot. What causes this?
Activation of coagulation Factors by physiological activator e.g. Tissue Factor
These activate eachother in a cascade like dominos
What are the final steps in the coagulation cascade
Prothrombin cleaved to Thrombin
Its then cleaves Fibrinogen to Fibrin which forms the clot
What natural Anticoagulants keep us from clotting outside sites of injury?
TFPI - switches off clotting factors 7 & 10
Proteins C & S - Switch off 5 & 8
Anti-thrombin - Switches of 5, 8 , 9, 10, 11 & thrombin
What triggers fibrinolysis?
Endothelial cells releaseing plasminogen activators (t-PA & u-PA)
What do Tissue Plasminogen Activators do?
They cleave plasminogen into plasmin --> breaks down fibrin --> Fibrin Degradation Products
what do we test for in a D-dimer?
Fibrin Degradation Products
Anti-thrombotic drugs include antiplatelets and anticoagulants. What types of antiplatelets do we have?
- Target adhering Gylcoproteins (Abciximab)
- Target surface receptors (Clopidogrel & Ticagrelor)
- Target Thromboxane 2 production (Aspirin)
Warfarin is a common anti-coagulant what does it do?
Reduces conc of various clotting factors inc 2, 7, 9, 10 & prothrombin
works by inhibiting Vit K
Other anti-coagulants include heparins and DOACs, what do DOACs do?
Direct Oral AntiCoagulants:
1) Rivaroxaban targets activated factor 10
2) Dabigatran targets thrombin
The clotting cascade starts in two different pathways and becomes the common pathway.
Which factors are involved in each pathway?
Intrinsic = 8, ,9, 11 & 12
Extrinsic = Tissue Factor (TF) & factor 7
They converge on 10
What test measures the function of each of the pathways in the clotting cascade?
Prothrombin time (PT) is a test of the extrinsic pathway
activated Partial Thromboplastin Time (aPTT) is a test of the intrinsic pathway
Thrombin is a product of the common pathway of clotting, what effect does it have on the intrinsic/extrinsic pathways?
It has a -ve feedback effect on the intrinsic pathway
What effect would Warfarin have on the aPTT & PT
could prolong both because it acts on both pathways