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What Is a Blood Clot?

By Kathy Dowling
Updated May 17, 2024
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Clotting is a critical process that allows damaged parts of the body to be maintained. When damage occurs to skin tissue or other tissue in the body in the form of a cut, blood starts to clot. A blood clot, or blood coagulation, is part of a process called hemostasis, and, during this process, bleeding stops because blood vessels restrict and a platelet plug is formed. Blood clotting is essential to body repair and maintenance and, without it, a cut would continue to bleed, causing a person to hemorrhage. An abnormal clotting condition called thrombosis arises when blood cells produce clots that travel through the bloodstream causing vessels to clog.

If the body’s tissue is damaged by a cut or other injury, chemical signals called chemoattractants activate thrombocytes, also called platelets. Thrombocytes are a type of white blood cell and, when activated, they disperse proteins within the body that work to seal damaged tissue. These white blood cells float freely in the bloodstream and act quickly and efficiently to clot blood after injury.

Thrombocytes release the proteins thrombin and fibrinogen when activated by chemical signals after injury. Thrombin works to alter fibrinogen which causes fibrin to be produced. Fibrin is a substance that causes blood to clot and is released extensively from thrombocytes rapidly after an injury has occurred. It is released in connective layers that begin to form around the outside of the cut, eventually moving inward and forming a blood clot. When the damaged region is sealed, white blood cells called leukocytes move to the area in order to prevent any contamination that may occur from bacteria or viruses.

When blood clots normally, it will usually form a breach in a vessel; however, this does not happen in all cases. A condition called thrombosis arises when blood does not clot properly. Abnormal clotting of fibrin can result in masses that break away from the clot and move freely though the blood stream. The floating blood clot is called a thrombus.

A thrombus can cause arteries, capillaries, and veins to be blocked, which are vessels that are important in supplying blood to particular organs in the body. Blocking occurs when the thrombus eventually moves through a vessel that becomes smaller in diameter. Once the vessel is blocked, oxygen, blood, and nutrients that are vital to the body will not be able to move past it, making thrombosis a serious medical condition.

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Discussion Comments
By subway11 — On Aug 02, 2011

@Bhutan - I remember years ago that a famous NBC newscaster, David Bloom died of a pulmonary embolism which was a blood clot in the lung.

They say that people that travel a lot and spend a lot of time sitting in an airplane have a higher chance of developing this condition which is very treatable if caught in time.

Unfortunately, he was overseas in Iraq when he suddenly died. Usually that is what happens with this condition, if you don’t get treatment you can die within a few hours. It is really scary.

By Bhutan — On Aug 02, 2011

@Mutsy - I wanted to say that a blood clot in the lung from time to time is common among lupus patients. My father in law's wife has lupus and had a blood clot in her lung as a result of this condition.

The doctor said that this condition is common among people with lupus and the doctor told my father in law’s wife to stay indoors when she got home.

She also had to have her blood checked every couple of weeks and is on a medication called warfarin which makes her really tired all of the time.

By mutsy — On Aug 01, 2011

@Starrynight – I know that some women do experience blood clots from birth control usage but it is a small number. I also wanted to say that blood clots are more common in pregnant women especially after delivery because they are in a stationary position for a long period of time.

I know that when I had both of my children the nurses wanted to me to take a few walks throughout the day in order to avoid blood clots in my legs from developing.

By starrynight — On Aug 01, 2011

@JessicaLynn - Developing deep vein thrombosis has been a fear of mine since I went on birth control pills. Recently, I actually had kind of a scare.

I went to the doctor because I was coughing and having some pain in my chest. I'm asthmatic, so I thought that's what the problem was. The doctor gave me a breathing treatment, but it didn't help. All of a sudden, the doctor totally freaked out, saying I might have a blood clot! She insisted on calling an ambulance and having me rushed to the hospital.

When I got there, I had all kinds of tests done. Fortunately, I didn't have a blood clot. I had bronchitis! I was torn between being glad I didn't have a blood clot and being angry at the doctor for not diagnosing me properly. You would think a doctor could tell the difference between a blood clot and bronchitis for goodness sakes!

By JessicaLynn — On Jul 31, 2011

Women who take birth control pills should keep in mind that deep vein thrombosis can be a side effect. This is when a blood clot forms in a vein in the leg. If it isn't taken care of, the clot can travel through the body to the heart of the brain and cause some pretty serious consequences. Symptoms to watch out for include swelling, localized pain, and the area being warm to the touch.

I actually thought this wasn't all that common. However, I actually know someone who developed deep vein thrombosis! It happened while she was on a plane and it was very scary. She is fine now, but she had to take blood thinners for quite awhile.

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