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Yr3 Haematology > Clotting > Flashcards

Flashcards in Clotting Deck (17)
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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?

Thromboxane A2


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


What effect would aspirin have on the aPTT or PT?

Aspiring inhibits COX enzymes preventing aggregation of platelets so it isn't involved in the clotting cascade