Cells in the blood that flows through our blood vessels can form into a lump known as a blood clot. Although a blood clot can lead to a potentially life-threatening condition, most blood clots are easily preventable.
What is a blood clot?
Blood normally flows through the blood vessels, with the heart pumping to push it through the arteries around the body, and muscles helping to push blood through veins. Blood clotting, or haemostasis, is a normal part of the body's healing process. If there is a cut or damage to a blood vessel, cells within the blood – including platelets and clotting factors – make some of the blood solidify and form a clot that adheres to the injured site, acting as a plug to stop bleeding. Blood clotting is also beneficial when there is a nosebleed, sprain, or other trauma. However, sometimes an unwanted blood clot can form such as when the blood does not circulate adequately.
What terms are associated with blood clots?
Doctors and medical specialists use different terms to specify blood clots in different situations.
- Thrombus: A blood clot (the plural is thrombi).
- Thrombosis: A thrombus, or blood clot, blocking a blood vessel (the plural is thromboses).
- Deep vein thrombosis (DVT): A blood clot that occurs in a vein, which is a blood vessel that carries blood back to the heart.
- Arterial thrombosis: A blood clot that occurs in an artery, a blood vessel that transports blood away from the heart.
- Embolus: A blood clot that breaks away and travels through blood vessels.
- Venous thromboembolism (VTE): The collective term that covers both deep vein thrombosis and pulmonary embolism (PE - an embolus that has travelled to the lungs).
- Thrombophilia: A group of medical conditions that can lead to blood clotting more easily.
Venous blood clots
Unwanted blood clots can originate in different parts of the body for different reasons.
In venous thrombosis blood clots form in a vein when there is prolonged lack of movement. Without contracting muscles to help push the blood through the veins, blood circulation slows down and can lead to blood pooling in an extremity such as a leg. The stagnant blood can form into small clots along the vein's wall, restricting the flow of blood returning to the heart.
Arterial blood clots
Blood clots in an artery, or arterial thrombosis, can form in people who have atherosclerosis - a disease that can result in heart attack and stroke - where plaque deposits that line the arteries lead to a narrowing of the blood vessels. The plaque can rupture, leading to a blood clot forming at the ruptured site, where it can block blood flow.
Blood clots can also form in the heart. In atrial fibrillation, the upper chamber of the heart, known as the atrium, has an erratic beat that allows the blood to become stagnant along the atrium's walls and form into small clots. Blood clots can also occur in a damaged ventricle after a heart attack.
Blood clots that are part of a normal blood clotting function can also cause medical problems. Blood clotting sometimes occurs during menstruation or abnormal vaginal bleeding in a woman, but if the clots are large they may be painful as they pass through the cervix. If a clot is associated with the urinary system, it can prevent the bladder from emptying. People with bleeding peptic ulcers can vomit blood that contains a clot, and clots can appear in bloody stools in people with rectal bleeding.