THE COAGULATION CASCADE Flashcards
All components are found in the [?].
circulating blood
To be activated, the blood must have direct contact with a foreign object such as a [?].
damaged blood vessel or glass
This results to absorption of [?] to the negatively- charged collagen exposed by vessel wall damage.
XII
- [?] is activated by the foreign material into [?]
Factor XII
XIIa
- [?] reacts weakly with [?], thus converting them into their forms
XIla
XI, prekallikrein (also by XIIf), and plasminogen
• Formed kallikrein feeds back to [?] and causes enzymatic cleavage producing more [?].
XII
XIla
- Xla in the presence of Ca** activates [?]
IX
• Note: IX can also be activated by [?]:
(CURRENT CONCEPT OF COAGULATION)
VIla-Ca*-TF complex
- IXa in the presence of [?] activates Х.
Catt, platelet phospholipids, and Villa
[?] is necessary for the activation of this system.
TISSUE FACTOR
All cells with the possible exception of those in the blood, contain [?].
tissue factor
When injury occurs, the [?] is released and acts as a cofactor in initiating coagulation.
tissue factor
The released [?] binds to VII and activates it to VIla.
tissue factor
Then [?] activates X to Xa of the common pathway.
VIla , together with calcium,
Begins with activation of factor X via the Intrinsic Pathway (?) or via the Extrinsic Pathway (?) to form Prothrombinase/[?].
IXaVIlla-Ca++-PL
VIla-Ill-Ca++
Xa-Va-Ca++-PPL
This prothrombinase complex converts [?] to thrombin which then cleaves [?] into fibrin.
prothrombin
fibrinogen
Conversion of Fibrinogen to Fibrin: STEPS:
1. Thrombin cleaves the a and B chains only (releasing [?]) forming soluble fibrin monomer/unstable gel.
2. Fibrin monomers aggregate spontaneously end to end, side to side to form soluble fibrin polymers thus vulnerable to enzyme [?] (also soluble in [?]).
3. [?] crosslinks adjacent fibrin monomers by forming COVALENT bonds to form stable and insoluble clot
fibrinopeptides A and B
plasmin; 5M urea
Factor XIII: XIlla + Ca++
What activates factor XIII to XIIIa?
Thrombin or Collagen
The key initiating step is the exposure of TF to the circulation and reaction of [?].
TF with factor VII
The [?] can enzymatically activate factors X and IX.
TF-factor/VIla complex
The initial activation of factor X to Xa may be important in getting the coagulation cascade started, however, tissue factor pathway inhibitor (TFP) rapidly inactivates the [?].
TF-VIla-Xa complex
The major action of the TFVIla complex in vivo is the activation of [?], which then activates [?].
factor IX to IXa
factor X to Xa
Consequently, [?] is converted to thrombin, then [?] is converted to fibrin.
prothrombin
fibrinogen
Factors [?] have positive feedback activity on earlier steps of the cascade
Xa and IIa
Activation of Coagulation
• It is [?]
autocatalytic or self-perpetuating
• Low level of thrombin activates [?] and [?]; Induces [?]
V and VIII
XIlI and XI
platelet aggregation
Inhibitor to Coagulation
• Controls
excessive coagulation
• Increase concentration of thrombin; destroys [?]; activates [?]
V and VIII
Protein C
increase plasminogen activation
Protein C and S
Promote plasmin generation (fibrinolysis)
Thrombin
: activates VIII to VIIIa
Factor II, X, residual thrombin (low level)
: activates FV
Thrombin, residual thrombin (low level)
: inhibits FV and VIII
residual thrombin (high level)
- regulatory mechanism to stop the cascade
inhibits FV and VIII
- continuous activation slows down the cascade
inhibits FV and VIII
- Thrombin is a very powerful protein that can activate many factor (FIX, FVII, FXIII)
inhibits FV and VIII
- to stop intrinsic pathway from accessing FX; FX will not be able to activate another thrombin/prothrombin to become thrombin
inhibits FV and VIII
: - forms soluble fibrin to insoluble fibrin
Fibrin XIIIa
- stabilizes the clot
Fibrin XIIIa
- soluble clot only forms fibrin meshwork (does not activate)
Fibrin XIIIa
may activate XII to XIIa
FXII + negative surface, Platelet
: procoagulant
Platelet
activates prekallikrein to kallikrein
FXII
activates HMWK to kinin (for the release of bradykinin. w/c participates in inflammation and pain cessation)
Kallikrein
activated form of HMW
kinin
uses HMWK as a cofactor to activate more FXII (feedback; autocatalytic with XII to XIIa)
Kallikrein
activates plasminogen to plasmin
XIII and Kallikrein