L.14 Haemostasis II Flashcards
(41 cards)
What was the first formal structure of blood coagulation introduced in the 1960s?
The waterfall and cascade models.
Who introduced the waterfall and cascade models of coagulation?
Davie and Ratnoff, and independently Macfarlane.
Define Haemostasis.
The physiological process that halts bleeding after vascular injury.
What are the components involved in the process of Haemostasis?
- Vasoconstriction
- Platelet plug formation
- Coagulation cascade
- Fibrin clot stabilization
- Clot dissolution via fibrinolysis
What does the Greek word ‘Haîma’ mean?
Blood.
What does the Greek word ‘Stasis’ mean?
To stop.
What is the role of Procoagulant (Thrombogenic) Elements?
To promote coagulation.
Name examples of Procoagulant Elements.
- Exposed subendothelial tissue
- Collagen
- Tissue Factor (TF)
- Platelets
- Platelet Activating Factor (PAF)
- Prothrombin
- Fibrinogen
- von Willebrand Factor (vWF)
- Coagulation factors
What is the role of Anticoagulant (Antithrombogenic) Elements?
To inhibit coagulation.
Name examples of Anticoagulant Elements.
- Heparan sulphate
- Thrombomodulin
- Tissue Plasminogen Activator (tPA)
- Antithrombin III
- Protein C
- Protein S
- Plasminogen
True or False: There is a delicate homeostatic balance between procoagulant and anticoagulant forces.
True.
What can disruption of the balance between procoagulant and anticoagulant forces lead to?
Haemorrhagic or thrombotic disorders.
What are the traditional groups of coagulation factors based on structural or functional features?
- Fibrinogen Family: I, V, VIII, XIII
- Vitamin K-dependent: II, VII, IX, X
- Contact Group: XII, XI, Prekallikrein, High-Molecular-Weight Kininogen
These groupings help in understanding the roles and interactions of coagulation factors in hemostasis.
Which factors are classified as Vitamin K-dependent?
II (Prothrombin), VII, IX, X
Vitamin K is essential for the synthesis of these factors, which are crucial for proper blood coagulation.
What is the significance of γ-carboxylation in Vitamin K-dependent factors?
It enables these factors to bind calcium ions and associate with phospholipid surfaces.
This post-translational modification is critical for the functional activity of the factors.
What clinical conditions can impair the function of Vitamin K-dependent factors?
Vitamin K deficiency or warfarin therapy
Both conditions can lead to increased bleeding risk due to reduced synthesis and activity of these factors.
What are the three pathways of the Classical Cascade Model?
- Extrinsic Pathway
- Intrinsic Pathway
- Common Pathway
These pathways describe the sequence of events leading to blood coagulation.
What triggers the Extrinsic Pathway in the Classical Cascade Model?
Vascular injury exposing Tissue Factor (TF)
Tissue Factor is a critical initiator of the coagulation cascade.
What is the role of Factor VIIa in the Extrinsic Pathway?
It binds to Tissue Factor and activates Factor X to Xa
This activation is essential for the progression of the coagulation cascade.
What initiates the Intrinsic Pathway?
Exposure of blood to negatively charged surfaces
This pathway involves a series of factor activations that lead to the activation of Factor X.
What is the sequence of activation in the Intrinsic Pathway?
XII → XI → IX, with cofactor VIIIa activating Factor X
This pathway is crucial for amplifying the coagulation response.
What does the Common Pathway culminate in?
Conversion of prothrombin (II) to thrombin (IIa)
Thrombin plays a key role in converting fibrinogen to fibrin, leading to clot formation.
What does thrombin do in the Common Pathway?
Cleaves fibrinogen (I) to form fibrin (Ia) and activates Factor XIII
This process stabilizes the fibrin mesh, essential for effective hemostasis.
What are the limitations of the Classical Cascade Model?
- Cannot explain why Factor XII deficiency doesn’t cause bleeding
- Cannot explain mild bleeding in Factor XI deficiency
- Cannot explain severe bleeding in Haemophilia A & B despite an intact extrinsic pathway
These limitations highlight the complexity of coagulation beyond the classical model.
