Blood clots normally form in response to an injury to a blood vessel, and they can develop in any part of the cardiovascular system. Blood clots are composed primarily of platelets (cell fragments in the blood that assist in clotting) and fibrin (an insoluble protein fiber formed as part of the clotting process). They may contain red blood cells as well.

Thrombi
A thrombus is a blood clot that adheres to the site of its formation, in the lumen (interior) of a blood vessel or in the heart. (Thrombus and the prefix thrombo- come from the Greek word thrombos, meaning a lump or clump.) Most of the time thrombi dissolve naturally and cause no problems. However, when they don't, they can partially block blood flow in a large blood vessel or block it completely in a smaller blood vessel. This may result in tissue death, as the flow of oxygenated blood is cut off.

Thromboembolisms
Thromboembolisms are the most common type of embolism. They are thrombi that break loose and are carried by the blood stream until they become lodged in a blood vessel, usually at a point where the vessel forks. The thromboembolism may plug a vessel in the lungs, causing a pulmonary embolism; the brain, causing a stroke; the heart, causing a heart attack; or the gastrointestinal tract, kidneys, or leg. In rare instances, other substances, such as a globule of fat, air bubbles, tissue from a tumor, or a clump of bacteria, may travel through the bloodstream as emboli and become lodged in an artery.

The majority of thrombi form in the veins, generally in the lower limbs. Arterial thrombi usually occur in people who have vascular (blood vessel) disease, commonly atherosclerosis. Thrombi may also form inside of the heart.

More on this topic

What Are Thrombosis & Embolism? (VIDEO)
Your Blood Moves
Thrombus & Embolus
Symptoms & Risk Factors
Blood Must Flow
Consequences of Clots
Tests & Diagnosis for DVT
Prevention & Treatment

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