Thrombosis (Greek: θρόμβωσις) is the formation of a
blood clot (
thrombus; Greek: θρόμβος) inside a
blood vessel, obstructing the flow of
blood through the
circulatory system. When a blood vessel is injured, the body uses
platelets (thrombocytes) 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. A clot that breaks free and begins to travel around the body is known as an
embolus.