When we injure ourselves and start to bleed, this is what happens:
- Our blood vessels become narrower. This reduces the flow of blood to the injured tissue, limiting the loss of blood.
- Blood platelets in the bloodstream, known as thrombocytes, attach to the damaged area of the blood vessel and clump together to reduce the bleeding.
- The body then activates a number of substances in the blood and the tissue. These substances solidify the clump by forming a special protein and fix the clump at the wound. These substances are called clotting factors or coagulation factors. There are 13 clotting factors in human blood and tissues. Most of them are made in the liver. The liver needs vitamin K to make some of these clotting factors. Our bodies cannot make their own vitamin K, so people have to get it in their diet.
Blood clots can also form even if the person does not have any external injuries. For instance, if blood flows too slowly and it starts to build up, large numbers of blood platelets may group together and stick to each other, forming a blood clot. It is also not uncommon for them to form because the inner walls of blood vessels are damaged, for example in atherosclerosis. If clotting factors are stronger, that can also increase the risk of blood clots forming for no identifiable reason. There are a number of reasons that this can happen, including a genetic predisposition, a tumor, or because somebody is taking a particular kind of medication. The medical term for a blood clot is “thrombus”.