What is the pathophysiology of embolism?

An embolism is the obstruction of the flow of blood by an embolus, a particle or aggregate of substance that is abnormally present in the bloodstream. When a thrombus, a blood clot, becomes dislodged and a piece breaks off, it is called an embolus. The embolus can obstruct the pulmonary circulation, and the body sends a signal to release neurohormonal substances and inflammatory mediators, which cause vasoconstriction.

Pulmonary embolism occurs when clots break off and embolize into the pulmonary circulation. Pulmonary emboli are typically multiple, with the lower lobes being involved more frequently than the upper, and bilateral lung involvement being more common. Once deep venous thrombosis develops, clots may dislodge and travel through the venous system and the right side of the heart to lodge in the pulmonary arteries, where they partially or completely occlude one or more vessels.