Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss. Even when a blood vessel is not injured, blood clots may form in the body under certain conditions. If a thrombus becomes too large, blood flow to the tissue supplied is reduced enough to cause symptoms because of decreased oxygen and accumulation of metabolic products like lactic acid. Learn more about thrombosis, its causes and treatments in this book.