What is thrombosis?

Thrombosis refers specifically to the formation of a blood clot within a blood vessel, which leads to the obstruction of blood flow. This clot can occur in veins or arteries and can cause various complications depending on its location. For example, if a thrombus forms in a coronary artery, it can lead to a heart attack by blocking blood supply to the heart muscle. The importance of this definition lies in understanding that thrombosis is characterized by the clot remaining anchored in the blood vessel where it was formed, which differentiates it from other conditions like embolism, where a clot dislodges and travels to another site in the circulatory system.

The other options do not accurately define thrombosis. A blood clot forming outside blood vessels would describe a hematoma or similar condition rather than thrombosis. Although thrombosis can contribute to conditions like heart attacks, it is not a condition in itself leading directly to such events. It's also not specifically a sign of high cholesterol levels, as thrombosis can occur due to a variety of risk factors unrelated to cholesterol, including blood stasis, endothelial injury, and hypercoagulability.