One of the human body's mechanisms for protecting itself from the life-threatening effects of blood loss is that blood has the ability to clot. Ordinarily, this is a good thing--bleeding wounds quickly clot and form scabs, keeping blood in the body where it belongs. Under certain conditions, however, blood clots can form in the blood vessels, which leads to serious effects and potential complications.
Formation
A blood clot forms as the result of damage to the lining of the blood vessel, under normal circumstances. When vessels are damaged and blood begins to leak, the vessels secrete chemicals that start a chain reaction involving many enzymes, Dr. Gary Thibodeau explains in his book, "Anatomy and Physiology." The enzyme thrombin converts an enzyme called fibrinogen to its active form, called fibrin. Fibrin then forms a net that catches platelets and red blood cells, producing a clot.
Causes
In general, blood vessels release chemicals that start the clotting cascade only when they're damaged. The damage, however, doesn't have to come from the outside. Some disease processes damage vessels sufficiently to cause them to form clots--atherosclerosis is one example. Dr. Lauralee Sherwood explains in her book, "Human Physiology," when cholesterol builds up in arteries and causes plaques to form, the arteries can harden and tear. This leads to clot formation in the arteries.
Considerations
Not all clots that form in vessels are the result of arterial damage. Deep vein thrombosis, the American Academy of Family Physicians (AAFP) notes, occurs in large veins, particularly those of the legs. If blood flow is reduced and blood starts moving through the veins very slowly, the blood can begin to clot and obstruct the vessels. This leads to clot formation and also prevents blood from passing through the vein and returning to the heart.
Effects
There are two major problems associated with occlusive, or vessel-blocking, blood clots. One is that when a clot blocks a blood vessel, it prevents blood from reaching tissues with nutrients carried in the bloodstream. The second problem is that if the clot breaks free of the blood vessel and begins to travel through the body, it can become lodged elsewhere. This, the AAFP notes, is called an embolus and can lead to heart attack or stroke.
Expert Insight
The risk factors for vessel-occluding blood clots include cardiovascular disease and atherosclerosis, which can lead to arterial clots. Other factors, however, increase an individual's risk of venous clot. The AAFP notes that advanced age, birth control pills, inactivity and recent surgeries all put patients at risk for blood clots in the veins, particularly the veins of the legs. Staying hydrated and moving around regularly increase blood flow and help to prevent clotting.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
- American Academy of Family Physicians: Thrombosis
