A blood clot or thrombus, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system (i.e. clotting factors).
A blood clot is normal in cases of injury, but pathologic in instances of thrombosis.
Specifically, a blood clot is the inappropriate activation of the hemostatic process in an uninjured or slightly injured vessel.
A blood clot in a large blood vessel will decrease blood flow through that vessel (termed a mural thrombus). In a small blood vessel, blood flow may be completely cut-off (termed an occlusive thrombus) resulting in death of tissue supplied by that vessel. If a thrombus dislodges and becomes free-floating, it is termed as an embolus.
Some of the conditions which elevate risk of blood clots developing include atrial fibrillation (a form of cardiac arrhythmia), heart valve replacement, a recent heart attack (also known as a myocardial infarction), extended periods of inactivity, and genetic or disease-related deficiencies in the blood's clotting abilities.
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