|
Extrinsic |
Intrinsic |
Meaning |
Requires a component extrinsic to blood |
Spontaneous clotting possible without extravascular exposure |
Main function |
Initiation |
Amplification |
Triggers |
Tissue factor (a tissue protein) |
Charged surface -In vivo: subendothelial collagen -In vitro: glass Factors: VIII, XI, XII |
Factors involved |
VII (and common pathway) |
XII, XI, IX, VIII (and common pathway) |
Speed |
15 seconds to activate “Thrombin burst” |
1-6 minutes to activate |
Amplification, importance |
Less |
More |
Dampening |
TFPI AT3 (see diagramme) |
TFPI AT3 Protein C (see diagramme) |
Interactions |
Xa activates TFPI, inhibiting TF/VIIa |
Thrombin -> activation of XI, VIII TF/VIIa -> activation of IX |
Implication of deficiencies |
? |
Factor VIII: haemophilia A Factor IX: haemophilia B |
Test |
INR = (PTpatient/PTnormal)ISI ISI: adjustment factor for each laboratory Citrated blood + TF + Ca2+ Time taken to clotting |
aPTT Citrated blood plus partial thromboplastin (phospholipid), Ca2+, silicate. Time taken to clotting |
Inhibitors |
Warfarin (Vitamin K epoxide reductase inhibitor; prevents γ-glutamyl carboxylation of factors II/VII/IX/X, prot C&S |
Heparin (potentiates AT3 effect on II and X) |
Effect of sepsis |
↑[VII] |
↑[kallikrein], [XI], [XII] |
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