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Deep Vein Thrombosis Health Center

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Blood Clots

Blood has a seemingly impossible job: It must flow continuously and smoothly throughout your body for an entire lifetime, but quickly shut off to prevent spills when you get a cut or injury.

Blood clots are healthy and lifesaving when they stop bleeding. But they can also form when they aren't needed and cause a heart attack, stroke, or other serious medical problems.

Recommended Related to DVT (Deep Vein Thrombosis)

DVT and the Risk of Pulmonary Embolism

When you have a deep vein thrombosis (DVT), you need to treat it to avoid a life-threatening complication: a pulmonary embolism. A pulmonary embolism (PE) usually happens when a blood clot in the leg breaks away, travels to the lungs, and blocks a lung artery. It can damage the lung and other organs and lead to low oxygen levels in the blood. It can even be fatal.

Read the DVT and the Risk of Pulmonary Embolism article > >

How Does Blood Clot?

The life cycle of a normal blood clot depends on a series of complex interactions.

1. Platelets form a plug. Tiny bits in your blood called platelets get "turned on" by triggers released when a blood vessel is damaged. They stick to the walls in the area and each other, changing shape to form a plug that fills in the broken part to stop blood from leaking out.

When activated, platelets also release chemicals to attract more platelets and other cells, and to set off the next step.

2. Chemical reactions grow the clot. Proteins in your blood called clotting factors signal each other to cause a rapid chain reaction, known as the coagulation cascade. This makes a protein called thrombin, which converts a dissolved substance in your blood into long strands of fibrin. These get tangled up with the platelets in the plug to create a net that traps even more platelets and cells. The clot becomes much tougher and more durable.

3. Other reactions stop its growth. Anticoagulant proteins, including antithrombin, protein C, and protein S, offset extra clotting factor proteins so the clot doesn't spread farther than it needs to.

4. Your body slowly breaks it down. As the damaged tissue heals, you don't need the clot any more. A protein called plasmin dissolves the tough fibrin strands, and your blood takes back the platelets and cells of the clot.

What Causes Blood Clots?

The process begins whenever flowing blood comes into contact with things called thrombogenic substances. Many of them are in your skin or in blood vessel walls, separated from blood. So when they touch, it usually means the skin or blood vessel wall is broken. Examples of these triggers are:

  • Collagen
  • Tissue factor
  • Von Willebrand factor

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