Thrombosis is the formation of blood clots while embolism is a clinical condition where break off small particles from clots, fat etc. comes and blocks an artery. These conditions may present the same if the blocked vessel is the same, but thrombosis blocks a blood vessel at a narrowed site while embolism may block healthy vessels, as well.
Thrombosis
Thrombosis is the formation of blood clots. After a wound platelets aggregate at the wound site to form a loose plug, the fibrin formation converts the loose plug into a definitive blood clot. Fibrin formation involves a cascade of reactions and a number of clotting factors. There are two pathways of blood clotting; the intrinsic and the extrinsic pathways. Both these pathways converge onto a common cascade, which results in the formation of a blood clot. Both these pathways have a common final result which is the activation of factor X.
Blood clotting – intrinsic pathway: At the start of the intrinsic pathway, a molecule called kininogen activates factor XII. This reaction occurs outside, when blood comes into contact with glass. Inside the body it starts when a damaged vessel exposes the underlying collagen fibers to clotting factors. Factors XI and IX activate sequentially. Factor IX binds factor VIII and activates factor X.
Blood clotting – extrinsic pathway: At the start of the extrinsic pathway, a molecule called tissue thromboplastin activates factor VII. Factors IX and X get activated subsequently. Factor X catalyzes the conversion of prothrombin to thrombin. Thrombin activates factor XIII. Final result is conversion of fibrinogen to fibrin. A fibrin meshwork forms around loose platelet plug and a definitive clot forms.
This phenomenon is of clinical significance when this occurs in a narrowed artery supplying an organ. When high lipid content promotes plaque formation on the arterial wall, the arteries get narrowed. When there is damage at the top of the plaque, a blood clot forms on top of the plaque further compromising the blood supply of the respective organ. This is what happens in heart attacks.
Clotting is very beneficial because it stops bleeding from skin wounds. It closes up a newly established portal of entry for infections. Clotting is essential for the success of surgical procedures.
Embolism
Embolism is a clinical condition where a small particle from a blood clot, fat, air, amniotic fluid, or placental tissue from a different site comes and blocks an artery. In patients who are bed-ridden or immobilized, blood clots may form in the deep veins of legs. This is called deep vein thrombosis. Clot embolism occurs when emboli from these shoot up and block the blood vessels in the lung. Fat embolism may occur where after a fracture, fat globules from bone shoot up to block the arteries. Air embolism occurs due to entry of air into the blood vessels in an amount that cannot be absorbed. During delivery, in external cephalic version and poly-hydramnios, amniotic fluid may enter the circulation. Placental tissue breaks off and enters the maternal circulation during pregnancy in minute amounts. In pregnancy induced hypertension, there is a higher risk of placental tissue embolism.
What is the difference between Thrombosis and Embolism?
• Thrombosis is clot formation while embolism is breaking off small particles from clots, fat etc.
• Thrombosis blocks a blood vessel at a narrowed site while emboli may block healthy vessels, as well.
• Both conditions may present the same if the blocked vessel is the same.
• Drugs that thin out blood prevent clot formation. Drugs that stop clotting stop clot embolism. Careful handling of fractured bones prevents fat embolism.