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Name: PAT
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Question:
Is there any common english answer explaining how various anticoagulants work? EDTA,Sodium Fluroide,Sodium Heparin, Lithium Heparin, Potassium Oxalate. I am having mid-terms next week and I really have not grasped the concept yet. All I understand is that they prevent the clotting of blood. That is not good enough!



Replies:
Blood clotting is actually a very complicated process. There are two pathways-the intrinsic system and the extrinsic system and there are 12 steps in the pathway for a blood clot to form. If you think about it, you don't want blood clots to form unless you really need them, so there are many steps which must be completed. When you first get an injury, the cells lining the capillaries are damaged and they release a chemical which attracts platelets to the area. The platelets are cells which stick together and form a temporary plug until a clot can be made. Then platelets release a factor which starts the clotting process on its way. Each step must happen in the right order for a clot to be finally formed. Also, some of the steps require chemicals such as calcium. So.... anticoagulants interrupt the process somewhere along the way. EDTA, sodium citrate and potassium oxalate for instance remove calcium from the blood. Heparin interrupts the last few steps of the process preventing thrombin from becoming fibrin. Diseases like Hemophilia are caused by lack of certain factors needed in steps along the way-ie. hemophilia is a lack of factor VIII (not actually the 8th step, they were named in the order they were discovered!) Hope this helps.

VanHoeck


Hi Pat! Yes they are substances that prevent blood clotting and so they are called anti-coagulants. Blood coagulation is a very complex phenomena and it is not easy to explain it without the use of some biological terms.

The anti-coagulation action is one that cuts of difficult that process at some of its stages. Let's see if telling you quite simply the coagulation process will let you undestand the anti-coagulation one.

When a blood vessel is broken, blood escapes as long as the flesh wound still is open, and the pressure within the vessel exceeds the outside one.Pressure can be equalized by different factors. Anyway usually shed blood clots quickly. Coagulation is a change that is studied by many scientists with different theories.

The clotting of blood is due to the sudden appearance of fibres that entangle the blood cells. During the very complex process, it occours the formation of a polymerized protein called fibrin from another protein, the fibrinogen.

Fibrinogen is produced by the liver and is converted to fibrin by the way of thrombin.

Thrombin does not exist in the normal circulation but is generated from a precursor, the prothrombin. Now prothrombin is a rather stable protein formed in the liver by a process requiring vitamin K, and any deficiency of this vitamin depress the production of prothrombin and also of other clotting factors.

Anyway if intravascular blood clotting is not prevented immediate death happens as the result. So there are natural inhibitory systems that destroy every activated clotting factor within a few seconds in the bloodstream.Their action, natural or induced (by drugs), correspond to the inhibition of the clot formation mentioned above.Six different factors inhibit thrombin formation. This action is greatly enhanced by heparin, a substance formed by connective tissue cells.

In a simple way we can say that the anticoagulant effect of any drug is to disturb the coagulation process.This can be done at different stages during that complicated process, acting differently upon the place and stage.

Hope that helps you, and thanks for asking NEWTON.

Mabel
(Dr) Mabel Rodrigues



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