Chapter 36 - Normal coagulation Flashcards
Overview of hemostasis
FIGURE 36.1
Vitamin K dependent proteins
Factor 7, 9, 10, 2 (prothrombin) Anticoagulant protein C, S, Z except for S and Z, the rest are serine proteases
Procoagulant proteins overview
TABLE 36.1
Anticoagulant protein, inhibitor and receptors overview
TABLE 36.2
Action of vitamin K
Reduces glutamate into gamma-carboxyglutamate allows protein to interact with Ca2+
Cofactor proteins in hemostasis
1) Factor V 2) Factor VIII 3) TF (tissue factor) 4) TM (thrombomodulin)
Molecular change of factor V leiden
arg506Gln mutation Slow to inactivate factor Va Leiden = prothrombotic
Factor VIII activation
1) by thrombin cleavage at 3 sites –> heterotrimeric cofactor VIIIa (lacks vWF binding site) 2) downregulated by spontaneous dissociation or by APC
Tissue factor keypoints
1) cell bound 2) non-enzymatic cofactor with Factor VIIa that activates factor 9 and 10
Thrombomodulin key points
1) cofactor for activation of protein C 2) cell bound 3) thrombin binds TM –> thrombin activity neutralized and inactivated 4) thrombin-TM complex activates protein C
Action of protein C-ase
1) inactivate cofactor Va and Factor VIIIa 2) suppress thrombin formation 3) activate thrombin-activatable fibrinolysis inhibitor (antifibrinolytic role)
4 vitamin-k-dependent enzyme complexes
FIGURE 36.4 1) extrinsic tenase complex: factor 7a, TF 2) intrinsic tenase complex: factor 9a, 8a 3) prothrombinase complex: factor 10a, 5a 4) anticoagulant protein case complex: thrombin, TM
Deficiency in hemophilia C
Factor 11
Factor 11 key points
1) catalyzed by thrombin to form 11a 2) function in propagation phase of thrombin generation
Proteins necessary for activation of intrinsic pathway
1) factor 12 2) prekallikrein 3) HMWK (high molecular weight kininogen)
Intrinsic pathway
1) factor 12 autoactivate to factor 12a when foreign surface 2) activated kallikrein and factor 11a kallikrein positively cleave HMWK more Factor 11a negatively regulates HMWK cleavage
Part of the three elements of the HMWK complex in intrinsic pathway
HMWK prekallikrein factor 11
Inhibitors of clot formation
1) antithrombin 2) tissue factor pathway inhibitor 3) heparin cofactor 2 4) protein C inhibitor
Incidence of congenital AT deficiency
1 in 2000-5000
Antithrombin key points
1) broad-spectrum anticoagulant 2) interacts with thrombin, factor 10a, 9a, 7a-TF, 11a, 12a, kallikrein, HMWK 3) potentiated by heparin and heparan sulfates (10000x)
Tissue factor pathway inhibitor key points
1) associated with lipoprotein 90% 2) cleared by liver, short half life 3) inhibits extrinsic tenase complex (7a-TF) 4) binds 10a and some forms of 5a
Texas bleeding disorder pathology
binding of TFPI and Va tightly due to factor V splice variant
Heparin cofactor 2 key points
1) inhibits thrombin ONLY 2) potentiated by heparin 1000x 3) increase in pregnancy, decrease in preeclampsia
Scott’s syndrome
improper presentation of platelet binding sites = pathologic hemorrhage
Granules in platelets
1) alpha granules = procoagulant, adhesive, fibrinolytic, antifribrinolytic 2) lysosomes 3) dense granules
Most potent activator of platelets
thrombin
Primary proteins of clot
1) fibrin 2) transglutaminase factor 13a
Interaction of clot proteins
1) fibrinogen bridges platelet aggregation 2) fibrin becomes insoluble 3) factor 13a stabilizes fibrin clot
Fibrinolytic proteins, inhibitors and receptors overview
TABLE 36.3
Hereditary plasminogen deficiency types
TYPE 1 = deficiency of plasminogen antigen and activity TYPE 2 = normal antigen level but reduced activity (dysplasminogenemia)
Plasminogen activation primarily inhibited by
PAI-1 PAI -1 reduces lifetime of plasminogen activators
Lysine analogues that block plaminogen activity
aminocaproic acid and tranexamic acid bind to protein lysyl residues prevent binding to plasminogen
Role of alpha-2 antiplasmin in vivo
Prevent plasmin activity beyond locale of fibrin deposition plasmin activity slower with alpha 2 antiplasmin than when free in solution
tPA binding
binds fibrin –> aligns binding to plasminogen
uPA function
1) promote degredation of extracellular matrix 2) triggers plasminogen activation and matrix metalloproteinase
half life of alpha 2 antiplasmin
2.6 days
Thrombin-activatable fibrinolysis inhibitor (TAFI) key points
1) plasma procarboxypeptidase B synthesized in liver 2) circulate in blood in complex with plasminogen 3) activated by thrombin-TM complex 4) removal of lysine residues in fibrin degradation prevents plasminogen binding site and activation
Initiation phase of coagulation
1) exposure of subendothelial TF binds circulating 7a 2) Factor 7a-10a complex (regulated by TFPI) 3) enough interaction to overcome TFPI 4) thrombin generation 5) activate platelets, factor 5, 8, 11 6) thrombin activates factor 13a –> fibrin formation
Propagation phase of coagulation
1) factor 8a combine with 9a on platelet –> intrinsic tenase complex 2) activate 10a and not under control of TFPI 3) combines with factor 5a –> prothrombinase complex 4) AT prevents inhibition of factor 10a and 9a
Termination phase of coagulation
1) thrombin bound to TM –> converts to anticoagulant enzyme = protein C-ase complex 2) cleaves factors 8a and 5a 3) TAFI activation prolongs clot lysis
Elimination phase (fibrinolysis) of coagulation
1) tPA generates plasmin at fibrin surface –> fibrin homeostasis 2) uPA binds to cellular uPA receptor to generate pericellular plasmin (matrix metalloproteinase) –> tissue remodelling and cellular migration
Prothrombin time uses
1) evaluate warfarin therapy 2) assess liver function 3) screen for deficiences in extrinsic and common pathway
prothrombin time steps
1) infusion of Ca2+ and exogenous TF-lipid preparation to citrated plasma 2) intrinsic pathway contribution negligible because of large amounts of TF-lipid use 3) standardize by INR 4) most sensitive to factors 2, 5, 7, 10 and fibrinogen
Activated partial thromboplastin time steps
1) phospholipid, Ca2+ and foreign surface to citrated plasma 2) absence of TF
Factors evaluated in aPTT
1) intrinsic pathway catalyst: factor 12, prekallikrein, HMWK, factor 11, 8, 9 2) common pathway: fibrinogen, prothrombin, factor 5, 10 3) test for hemophilia A (F8), B (F9), monitor heparin therapy, detect lupus anticoagulant
Thrombin time (TT)
1) detects direct inhibitors of thrombin or fibrin polymerization 2) distinguish between problem in thrombin generation or thrombin inhibition
Thrombin generation assay
1) thrombin once produced, hydrolyzes specific substrate to give fluorescent signal 2) continuously recorded to give evaluation of the phases of thrombin generation
Platelet function tests
1) platelet aggregometry 2) platelet function analyzer 3) flow cytometry 4) molecular biology techniques
Platelet aggregometry uses
test how agonists affect platelets in the milieu of plasma/whole blood
Activated clotting time
Adjusted aPTT for samples of citrated whole blood
Thromboelastography
1) measure increasing velocity of blood during coagulation process producing time-based record 2) Rotational thromboelastography or thromboelastometry
