Biochem Bloodclotting Exam 7
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How does TFPI work?
This is tissue factor pathway inhibitor which is an anticoagulant. It binds extrinsic tenase (complex of factor VIIa,CA2+,TF) and prevents conversion of prothrombin to thrombin (factor X to Xa).
How does anti-thrombin & heparin work?
Heparin is an anticoagulant. It increases the affinity of anti-thrombin for thrombin (factor IIa). This prevents conversion of fibrinogen to fibrin (factor II to IIa).
Describe the the thrombomodulin/protein C pathway.
- Punch Line: Inactivates factor VIII and factor V. THese are the two, 3 form cofactors required in intrinsic tenase (factor IXa complex) and prothrombinase complex (factor Xa complex) respectively.
- Anitcoagulative pathway. Thrombomodulin is an endothelial membrane bound molecule (by Ca2+ bridge) which can complex with free floating thrombin (IIa). The complex activates protein C (PC) to APC. APC in turn combines with its cofactor protein S (PS). This APC/PS complex can now inactivate two important molecules, intrinsic tenase complex and prothrombinase complex by inactivating the 3 form cofactors that go with each.
Factor V Leiden mutation (Arg506Gln)
increased risk of venous thrombosis
What is plasmin? What does it do?
Plasmin is a serine protease. It dissolves fibrin clots by breaking fibrin.
What molecule crosslinks fibrin? What amino acids participate in this bond?
The transglutaminase, factor XIII crosslinks fibrin by making glutamine/lysine bonds.
What 2 molecules activate plasminogen?
tPA (tissue plasminogen activator); urokinase
Determine whether the following leads to clot formation or degradation. (alpha2-plasmin inhbitor, APC/PS complex, Thrombomodulin/IIa complex, PAI-1)
- alpha2-plasmin inhibitor: clot formation
- APC/PS complex: clot degradation
- Thrombomodulin/IIa complex: clot degradation
- PAI-1(plasminogen activator inhibitor): clot formation
Most common hemorrhagic disorder due to a deficiency in factor VIII. x-linked disease (passed from mother to son)
Hemorrhagic disorder due to a defect in factor IX (intrinsic tenase)
von Willebrand disease
Hemorrhagic disorder due to a defect in vWF. Affects collagen binding GP1B95 and chapperone of factor VIII so factor VIII degrades.
Bernard Soulier Syndrome
Hemorrhagic disorder due to a defect in GP-1B95
Hemorrhagic disorder due to a defect in GP-2b/3a
Most molecules in the coagulation cascade are bound to phosopholipid on cell membranes, by a Ca2+ bridge, in the active form. This includes extrinsic tenase (VIIa), intrinsic tenase (IXa), and prothrombinase (Xa). What factor is free floating (not bound to PL) in the active form? Why is this dangerous?
Thrombin (factor IIa); It can travel through the blood vessel and form clots (by converting fibrinogen to fibrin) in a region of blood vessel that is not injured. Anticoagulatants are present in the blood to prevent this.
The activation of what two cofactors does thrombin feedback upregulate? What else does thrombin trigger?
Factors VIII and V. Thrombin also triggers the intracellular cascade in the cellular response via thrombin receptor.
What are the four final stages of the coagulation cellular response? What is the cellular response?
- Cellular response is platelet activation by collagen. Following the intracellular cascade there is
- 1. Secretion of vasoconstrictors (seratonin and throm. A2), growth factors, Ca2+, and ADP
- 2. Activation of GP-2B/3A
- 3. Conformational change in platelet to explose PL and Ca2+
- 4. formation of Hemostatic plug by aggregation of platelets through fibrin and GP-2B/3A.
Describe what occurs initially in the cellular response to vascular injury.
Collagen is exposed from the endothelium. Collagen binds three cell surface molecules (integrin a2B2, GP-1B95 via VWF, and GP-6). GP-6 and activation of thrombin receptor by thrombin (from molecular response) triggers the intracellular cascade. Eventually this leads to platelet aggregation.
Describe the intracellular (inside the platelet) cascade in the cellular response to vascular injury. What 2 events trigger the intracellular cascade. Where does aspirin interfere with this pathway?
- The IC cascade is triggered by
- 1. activation of GP-6 by collagen binding
- 2. activation of the thrombin receptor by thrombin (molecular response).
- The IC cascade is as follows: PIP2 makes DAG and IP3. IP3 releases intracellular Ca2+. The Ca2+ allows conversion of phospholipids to Thromboxane A2 via COX enzyme. Ca2+, DAG and Thromb A2 all 3 trigger the final stages of platelet activation and aggregation.
What role does Aspirin play in coagulation?
Anticoagulant. Aspirin is a COX inhibitor so it prevents platelet activation and blood coagulation.
What role does vitamin K have in coagulation?
Vitamin K is a cofactor for the enzyme carboxylase. Carboxylase typically coverts glu residue to a gla residue. Gla is a stonger Ca2+ chelator and aids in bringing proteins (factors IX, VII, X, PC, and PS) to the platelet surface. Ca2+ acts a bridge between the Gla residue and the (-) charged head groups of platelet phospholipids.
What is the mechanism of the drug Warfarin? What problems may occur?
Warfarin is an orally administered anti-coagulant. It prevents reactivation of Vitamin K. This in turn blocks carboxylase activity and activation of cascade clotting factors. The amount of warfarin must be carefully administered since the therapeutic range is small. To much warfarin can cause hemorraging.
Anticoagulant. Blocks ADP receptor and prevents platelet activation.
Anticoagulant. Blocks GP-2B/3A and prevents platelet aggregation.
Anticoagulant derived from leeches. Blocks thrombin.
What is the difference between arterial thrombosis and venous thromoembolism?
- Arterial thrombosis is a result of artherosclerotic plaque, which if ruptures the endothelial cells of the vessel wall, will initial platelet formation (need platelet therapy).
- Venous thromboembolism is a blood clot in the upper leg due to vascular defect. This clot if released can travel to the pulmonary artery and cause a problem there.
What is the first step in measuring clotting function?
stop coagulation with a Ca2+ chelator.
APT Time What can it measure and how should coagulation be initiated?
Tests all factors except factor VII. Initiate coag. with Ca2+ and (-) surface.
PT What can it measure and how should coag. be initiated?
Tests everything in extrinsic and common pathway. Intiate coag. with ca2+ and tissue factor.
TT What can it measure and how should coag be initiated?
Tests specifically for fibrinogen (factor II). Initiate coag. with Ca2+ and thrombin.
What does fucosyltransferase do? What gene encodes for the anitgen on RBC and body secretions? WHat percent of population is homo for recessive allele in each case?
- It transfers a FUC group from GDP-Fuc to precursor type 2 to produce H-antigen.
- H locus FUT-1 encodes H antigen on RBCs (very rare to be h/h except in Indian population).
- Se locus on FUT-2 encodes H antigen on body secretions (20% se/se; can still have antigen on RBC)
What sugar is added to H antigen to produce A antigen. How about B antigen? What enzymes are responsible for each?
- A antigen: A transferase ---> GalNAc
- B antigen: B transferase ---> Gal
What is the phenotype for Bombay bloodtype? What antibodies are made in these individuals?
Phenotype h/h se/se; Will produce anti-H, anti-A, and anti-B antibodies
What class are ABO antibodies?
mostly IgM; do not cross the placental membrane
What class are Rh antibodies? Why is this problematic during pregnancy?
IgG mostly; These proteins can cross the placental membrane and under certain conditions, can attack the fetal erythrocytes.
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