How Thrombosis Occurs

Blood Clotting Mechanisms Are Essential but Potentially Dangerous

Jan 22, 2008

We wouldn't live long without an effective blood clotting mechanism but when things go wrong the consequences of thrombosis can be fatal.

Thrombosis is the process of blood clotting. Blood clotting is essential for well-being and survival. Without a clotting mechanism we would not only bleed to death following relatively minor wounds, we would bleed under the skin and into our joints as haemophiliacs know only too well.

As is often the case in disease, the problem is due to an essential body process going wrong or being triggered inappropriately. Basically a clot forms inside an artery or vein when it shouldn't.

Clotting Mechanism

This is a complex processe involving numerous factors. Central to the process is the platelet cell. These small cells circulate freely in the blood until they encounter damage to the inner wall of a blood vessel. Substances released from the damaged wall cause the platelets to aggregate in the area. They also become sticky and form a plug for the damaged tissue.

The platelets in turn release substances that trigger the various clotting factors in the blood. The net result of all this is the formation of fibrin – a sticky stringy protein that forms a mesh which nets the circulating red blood cells to form a blood clot.

The Clotting Triad.

In the 19th century, the German pathologist Rudolf Virchow suggested that one or more aspects of a triad must exist to trigger the clotting process. This triad holds good today; the three aspects are: damage to the inner wall of the blood vessel, disruption to the flow of blood and chemical changes in the blood.

Damage to Blood Vessel Wall

The most obvious cause of this is trauma when of course, clotting would be appropriate. However the most common cause of clotting for this reason is atheroma -the development of fatty plaques in the vessel wall associated with high cholesterol levels.

Disruption to Blood Flow

Muscles, particularly those of the lower limbs, form an important pump to assist the heart in maintaining circulation. Any situation which immobilises the muscles for long periods increases the risk of clot formation, for example: flying, long car journeys, being bed ridden.

Chemical Changes in the Blood

Various changes in the blood, particularly those involving changes in hormone levels, will tend to increase the likelihood of clot formation. Examples include pregnancy, the menopause and the contraceptive pill. Some cancers and infections can also provoke clotting.

Consequences of Thrombosis.

The consequences of clot formation within blood vessels are potentially dangerous. The most serious occurrences are listed below.

Deep venous thrombosis (DVT): usually occurs in lower limb or pelvis, sometimes producing pain or swelling. The danger can come from parts of the clot breaking off and travelling to the lungs giving rise to pulmonary embolism.
Pulmonary embolism: features are pain in the chest and breathlessness. Can be fatal if not treated quickly.
Myocardial infarction: death of heart muscle from blockage of the coronary arteries by a clot, often secondary to atheroma formation in the blood vessel. Can also be fatal.
Stroke: a clot in the blood vessels of the brain can starve parts of the brain of glucose and oxygen and result in loss of neurological function.

Prevention

Knowledge of the clotting triad points to appropriate prevention measures. Eating a healthy diet rich in fruits and vegetables will help prevent atheroma formation and protect the inner wall of blood vessels.

Regular exercise will allow the muscle pumps in the legs to help the heart maintain a good circulation. If possible try to break up long periods of sitting with a short walk or flexing the calf muscles.

A healthy diet and regular exercise will improve immunity and reduce the chances of infection and cancer.

This article is for information only. Consult a doctor if you have any health concerns.