Second midterm - hemostasis (unfinished) Flashcards
Define hemostasis
Ability to arrest bleeding from injured part of blood vessel and to prevent thrombus formation inside the blood circulation.
What kind of enzyme is thrombin, what are its actions and where is it made?
Serine protease.
1: Fibrin formation from fibrinogen
2: Activation of platelets (PAR-receptor)
3: Activation of factor 5, 8, 11 and 13
Synthesized in the liver as prothrombin where its concentration is around 2 microM. Factor 10a converts it to thrombin (also a serine protease).
Where are fibrinogen synthesized and what are its structure?
What part of fibrinogen does thrombin hydrolyse?
Factor 1. Made by the liver. Concentration is around 10 microM. 2x3 protein chains. These chains are held together by S-S bonds. The chains consists of Aalpha, Bbeta and gama chain. The middle portion is known as the E-region and the ends is both called D-region. Fibrinogen are water soluble, fibrin are not.
Thrombin hydrolyze the residues between 16-17 (on Aalpha chain) and 14-15 (on Bbeta chain) on the N-terminal. Fibrinopeptide A and B are released and the remaining part is called a fibrin monomer. Factor 13a cross-link these monomers
Why is it important to remove fibrinopeptide A and B from fibrinogen?
A and B covers the binding sites on E-region. When they are removed by Thrombin, these sites can interact with the D-region on other neighbouring fibrin monomers.
Cross-linkage occur between Lys and Gln groups of gama-chains (formation of isopeptide bonds) by factor 13a (transglutaminase)
What is “Gla”?
Gama-carboxyglutamate. Formed by post-translational modification of glutamate by a carboxylase in the presence of reduced Vitamin K where CO2 is incorporated into glutamate
Found on factor 2, 7, 9, 10, protein S, C and Z
Vitamin K reduction is inhibited by?
Coumarin (vitamin K antagonists). Warfarin
What formes a “prothrombinase complex”?
Phospholipid membrane, Ca2+, Factor 5a, Factor 10a and prothrombin”
Intrinsic tenase complex need?
Cofactor 8a, Ca2+, phospholipid membrane, factor 10 and factor 9a
Which proteins contains Gla-domains?
Factor 7, 9, 10, protein C, protein S, protein Z and prothrombin (factor 2)
What factor defects are present in haemophilia A, B and C?
A: Factor 8
B: Factor 9
C: Factor 11
What can activate platelets? What inhibits is activity?
ADP, 5-HT, TXA2, Thrombin
NO and PGI2
vWF can bind to which GP on platelets?
GP1b, GP2b/3a (primary for vWF)
GP2b/3a (“fibrinogen receptor”) is important in a “inside-out” signal -> Platelet aggregates. RGD-sequence function as a bridge (argeine-glycine-aspartate motif) and form a primary plug.
Which factors inhibit blood coagulation
Protein C, antithrombin, tissue factor pathway inhibitor and protein S
What is the “alternative pathway”?
Factor 7-TF complex can activate factor 9.
What inhibits the activtion of Xa by Factor 7-TF complex almost immediately (extrinsic pathway)?
Tissue factor pathway inhibitor (TFPI). Anti-coagulation protein what acts as a serine protease inhibitor. Released by thrombin activation of PAR1 receptor -> Inactivated factor 7a and 10a.
- NET with neutrophil elastase break down TFPI and by doing so, inhibit the extrinsic tenase complex which leads to enhanced coagulation.
What are thrombin-activatable fibrinolysis inhibitor (TAFI) and its significanse?
Inhibit fibrinolysis.
Cleave C-terminal residues on fibrin (arg and lys residues). Eliminates binding sites for plasminogen and tPA on fibrin.
TAFI is stimulated by thrombin on thromomodulin. TM have both profibrinolytic and anti-fibrinolytic effect. Its via inhibition of thrombin formation and decrease of TAFI activation that protein C exerts it’s profibrinolytic effects.
Function of alpha-2-Macroglobulin?
Alpha 2 macroglobulin inhibit plasmin, kalilikrein and thrombin.
- acts as an antiprotease and is able to inactivate an enormous variety of proteinases. It functions as an inhibitor of fibrinolysis by inhibiting plasmin and kallikrein. It functions as an inhibitor of coagulation by inhibiting thrombin.
Platelets can bind to vWF by which receptors?
GP1b (primary)
GP2b/3a is for fibrinogen after activation and flipping of the PL in the PM
Does factor 13 circulate freely in plasma?
No, they are bound as a hetrotetramer (2 catalytic A domains and 2 carrier B domains). Thrombin in the presence of Ca2+ and fibrin as a cofactor (exosite 1) remove these B units.
Factor 13 is hydrophobic.
What bind to thrombin exosite 1 and 2?
1: Fibrinogen, PAR-Receptor and some coagulation factors
2: Heparin and GP1b-9-5
Thrombomodulin: Where is it found and what is its function?
hint: thrombin
Expressed on the surface of endothelial cells and serves as a cofactor for thrombin (bind to exosite 1). Thrombomodulin functions as a cofactor in the thrombin-induced activation of protein C in the anticoagulant pathway by forming a 1:1 stoichiometric complex with thrombin. This raises the speed of protein C activation thousandfold.
Thrombomodulin-bound thrombin has procoagulant effect at the same time by inhibiting fibrinolysis by cleaving thrombin-activatable fibrinolysis inhibitor (TAFI,aka carboxypeptidase B2) into its active form. This thrombin induced activation of TAFI inhibits fibrinolysis.
Warfarin (dicourmain) action
Inhibit GLA synthesis by inhibiting Vitamin K Epoxide reductase. Not able to reduce vitamin K.
GLA formation require reduced Vitamin K, CO2 and O2
What can activate “the contact pathway”?
High-molecular-weight kinogen (HMWK), prekallikrein and factor 12
Polyphosphate (poly-P), RNA, DNA can activate factor 12
Function of antithrombin
Most important inhibitor of thrombin, free factor 10a, 5, 9, 10 and 12
