Thrombus

Thrombus is another word for a blood clot. It forms when there is damage to the blood vessel. Platelets stick to the damaged vessel, attracted by the exposed collagen. The platelets form a platelet plug and stop the external bleeding. Chemicals released from the site attract clotting factors (see Clotting Cascade) which lead to fibrin formation. The fibrin sticks together and seals the wound forming the blood clot.