Coagulation Notes

Gregory Tetrault
These notes correlate to the slides in the powerpoint lecture. Handout in class follows slides as well.
Handouts, etc. on Blackboard.
Not too many notes to take.
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Clinical pathology covers all testing and blood banking.
Hemoostasis-regulation of blood volume inside you. Hemodynamics is about blood flow.
Sepsis- one of main casuses of death is inappropriate coagulation in all capillaries of body triggered by bacterial toxin.
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Objectives
(topics in handout file)
Many homeostatic systems have multiple checks and balances.
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Abbreviated schematic of major parts of coagulation cascade. Intrinsic pathway statrts at endothelial surface. Thrombin reacts there. Factor 11 converts to little a activated factor. Little a form is smaller because a part is cleaved off. Often you get 2-3 cleavage products, one of which is active product.
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Clotting factors cleave proteins. A cascade of enzymatic reactions occurs. Each curved arrow is an enzymatic reaction. At end protein fibrinogen cleaved to fibrin, crosslinked, stable clot forms. Not crosslink, clot will not hold and washes away.
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important facts- Many steps need free ionized Ca. Without Ca, clotting does not occur. Why doesn’t donated blood clot? Bag contains citrate to chelate Ca. EDTA or citrate can be used when drawing blood. Binds Ca.
Intrinsic pathway needs HMWK and prekallikrein(not a proteolytic enzyme).
Platelets are part of regular clotting. They can form plugs to block leakage and can release phospholipids. If they do not work, cannot prevent any kind of bleeding.
Some active factors trigger formation of anticoagulants as part of feedback regulation.
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Every clot triggering event is damage to epithelial layer of blood vessel. Exposure of collagen activates factor XII, Tissue factor can leak from damaged tissue like skin. Factor 11a circulates. Kallikrein stays at injury site in complex.
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HMWK acts as anchor. XIa cleaves IX to IXa in a Ca dependent way.
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Factors numbered in order of discovery, not function.
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Always small amount of thrombin in plasma.
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Damage to subendothelial cell membranes- tissue factor without collagen and HMWK activates extrinsic pathway. Can trigger boh pathways activating at same time.
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Common pathway
Clotting factors trigger more and more activation as you go along.
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Thrombin action.
XIIIa catalyses crosslinking monomers.
When thrombin cleaves receptor on platelet, causes aggregation. Degranulation provide phospholipids.
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Photomicrograph shows early microscopic clot with platelets in fibrin mesh.
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Natural anticoagulantss prevent runaway clotting- do not work perfectly.
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Once damage is patched, need clot to dissolve. Otherwise would have permanent clots and reduced function.
Can run out of fibrinogen. Uncontrolled clotting can result in uncontrolled bleeding from other sites.
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Heparin used to prevent unwanted clotting, but almost never used outside hospital. Must be injected or given intravenously.Potentiates Antithrombin III. Easy to overdose. Must be monitored carefully. There is a reversing drug- polycation binds to heparin to deactivate.
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Inhibits here.
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heparin cofactor II is native inhibitor of clotting. Inhibits thrombin only. Binds thrombin and physically blocks active site. Heparan sulfate and dermatan sulfate are GAGs or acid mucopolysaccharides on cell membranes. Since GAGs are on cell membranes, they inhibit thrombin near intact cells so clot does not cover them. Clot limited to site to damage.
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3rd inhibitory system proteins labelled with letters. Endothelial cell Thrombin receptor activates protein C. Protein S attaches and complex inactivates factrs V and VIII (common pathway)
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4th systems
tissue factor pathway inhibitor
protein circulates in blood. Inhibits extrinsic pathway, not intrinsic pathway.
Coagulation reversal
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Acute scenario- all you need is clotting and inhibition. Gives balance so clots form when needed and don’t when not needed.
Plasmin breaks down fibirn network of clot.
tPA cleaves plasminogen
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FDPs protein fragments released into blood. Inhibit more clot formation. D dimers have structure that can be analysed. Concentration tells rough size of how much clot degraded.
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Clotting factor facts in table. Will encounter literature that uses these terms.
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biochemistry
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FactorXII
Low-medium molecular weight protein. Sequence homology with plasminogen activator and fibronectin. Clotting activator has homology with clot dissolver component. Fibronectin in pregnancy is involved with integration of placenta with uterine wall. Marker of premature labor. False labor, baby is not in jeopardy. Differentiate true from false by monitoring level of fibronectin. Premature labor needs to be monitored and drugs used.
Has EGF-like activity. Not normal function. EGF helps skin and mucus membrane to grow.
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Fragments do not separate after cleavage, but conformational change reveals active site. Heavy chain may be degraded further.
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Factor XI
Least common form of hemophilia is due to this. Most mutations are harmless. Forms 2 products. Smaller is active as before. Deactivates by alpha-1-antitrypsin. Enzyme produced by liver. Activated trypsin is supposed to only be in intestine. If it gets into blood, really dangerous. General protease. Specific enzyme cleaves trypsin.Also deactivated Factor XI.
There can be deficiencies of antitrypsin- get liver cirrhosis and pulmonary fibrosis. Causes liver transplant. New liver has right genes. Transplant is curative if do it before lungs get too bad.

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Factor 9 –hemoB Gene on X chromosome. Woman carrier, male affected.
Requires vitamin K- many clotting factors require vitamin K for polycarboxylation to occur for factor formation in liver. Vitamin K deficiency causes coagulation problems. Coumadin is rat poison. Warfarin inhibits vitamin K.
Stays together after cleavage. Heavy chain has EGF like region, unknown why.
Heavy chain is where polycarboxylation happens.
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Large protein. Most common form hemophilia. Multiple chains. Gene with 26 exons on X chromosome. Takes 2 cleavages to get activated factor.
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Factor X 11-12 Ca binding sites. Affected by Ca deficiency. Alters conformation and confers enzymatic activity.
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Factor V
Vitamin K dependent
Factor V can deactivate itself if high concentration Va exists. Ca dependent. Ca bridges hold parts together. Leiden mutation- molecule works fine, but does not get degraded by protein C. Causes excess clotting. Risky for pregnant women- pelvic veins can clot off.
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requires vitamin K. Ca dependent area. Needs Ca and binding to phospholipids.
Heavy part is active form because it is a small protein.
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Factor I
Fibrinogen. Blue are alpha chains. Mirror image proteins.Green is beta. Cleavage is at small black arrows in center. End can bind to gamma chain on different fibrin strand.
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Staggered fibrils form. Forming link requires factor XIIIa. Need cleavage, then catalysis and assistance for steric lining up.
XIII transglutaminase.
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Crosslink forms Gln-lys bridge to stabilize loose interactions. Harder to fall apart.
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Conclusion
Reversal pathway has no redundancy.