18 Questions
What is the molecular weight of Factor V?
330,000 Daltons
Which coagulation factor is known as the labile factor?
Factor V
What is the half-life of Factor V?
12-36 hours
Which coagulation factor requires vitamin K for its synthesis?
Factor VII
Which coagulation factor is fully consumed in the process of coagulation?
Factor V
What is the molecular weight of Factor VIII?
1.2 million Daltons
What are the two pathways that initiate the coagulation process?
Intrinsic pathway and extrinsic pathway
Which factor is activated on the surface of platelets that leads to the formation of fibrin strands?
Factor X
What is the function of PF3 in the coagulation process?
Phospholipoprotein of platelets
What is the active form of kallikrein?
Prekallikrein
Which coagulation factor does not depend on vitamin K for its production?
Fibrinogen (Factor I)
What is the molecular weight of Fibrinogen (Factor I)?
340,000 Daltons
Explain the role of Prekallikrein (Fletcher Factor) in the coagulation process.
Prekallikrein activates plasminogen and is a precursor for kallikrein, which acts as a chemotactic factor for phagocytes.
Differentiate between the Fibrinogen Group and the Prothrombin Group of coagulation factors based on their properties.
The Fibrinogen Group (Factors I, V, VIII, XIII) is consumed during the coagulation process and their activity is lost in serum, while the Prothrombin Group (Factors II, VII, IX, X) is dependent on vitamin K for synthesis and most factors in this group are not consumed during coagulation and are present in serum.
Explain the significance of the Contact Group of coagulation factors (Factors XI, XII, Prekallikrein) in the coagulation process.
The Contact Group factors are not dependent on vitamin K or calcium for their synthesis and activation. They are stable and well-preserved in stored plasma, indicating their importance in initiating the coagulation process.
Describe the two pathways that lead to the activation of prothrombin in the coagulation process.
The two pathways are the intrinsic pathway and the extrinsic pathway, both of which converge into a common pathway that ultimately leads to the activation of prothrombin.
Explain the role of High-Molecular-Weight Kininogen (HMWK, Fitzgerald Factor) in the coagulation process.
HMWK is a cofactor in the activation of Factor VII, which is a key component of the extrinsic pathway of coagulation.
Describe the factors that influence the levels of Factors V and VIII in the coagulation process.
Factors V and VIII lose activity in stored plasma, and their levels increase during inflammation, pregnancy, and in women taking oral contraceptives.
Study Notes
Coagulation Factors
- Coagulation cannot occur without calcium, and substances that bind calcium can be used as anticoagulants, such as EDTA.
- There are 13 coagulation factors, which are protein in nature and become active enzymes after activation.
Factor V (Proaccelerin)
- A globulin with a molecular weight of about 330,000 daltons.
- Synthesised in the liver and is labile, deteriorating rapidly in oxalated plasma, even when frozen.
- Does not require vitamin K for its synthesis.
- Essential for the prompt conversion of prothrombin to thrombin in both the intrinsic and extrinsic pathways.
- Fully consumed in coagulation, with a half-life of 12-36 hours.
Factor VII (Proconvertin)
- A beta-globulin with a molecular weight of 48,000 daltons.
- Synthesised in the liver and is dependent on vitamin K.
- Not consumed or destroyed in the process of coagulation.
- Has a very short half-life of about 4-6 hours, but is stable in citrated plasma for up to 2 weeks at 4°C.
- Takes part in the extrinsic pathway of coagulation by activating the tissue thromboplastin.
- Converts factor X to factor Xa.
Factor VIII (Antihaemophilic Factor)
- A high molecular weight (1.2 million daltons) beta-globulin.
- Site of synthesis is not yet clearly identified, but it is not dependent on vitamin K.
- Has a short half-life of 6-10 hours.
Coagulation Pathways
- The coagulation process is a cascade of factor activities, initiated by:
- Interaction of certain clotting factors with the collagen fibres beneath the endothelium (intrinsic pathway).
- Release of a lipoprotein tissue factor (extrinsic pathway).
- Both pathways ultimately activate factor X on the surface of the platelets and finally lead to the formation of fibrin strands.
Other Coagulation Factors
- Factor I (Fibrinogen): a plasma protein with a molecular weight of 340,000 daltons, synthesised in the liver, and does not depend on vitamin K for its production.
- Prekallikrein (PK): synthesised in the liver, not dependent on vitamin K, activates plasminogen, and is a precursor for kallikrein.
- High-molecular-weight kininogen (HMWK): produced in the liver, does not depend on vitamin K for its synthesis, and is a cofactor in the activation of factor VII.
Classification of Coagulation Factors
- Fibrinogen Group: Factors I, V, VIII, XIII.
- Prothrombin Group: Factors II, VII, IX, X.
- Contact Group: Factors XI, XII, Prekallikrein.
Test your knowledge on the intrinsic and extrinsic pathways of the coagulation cascade, leading to fibrin formation. Understand the activation of clotting factors and the role of platelets in the process.
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