What Is Inflammation? - Definition, Causes & Symptoms

Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

When the body is attacked by something it deems harmful, a response called inflammation often occurs. Learn the definition of inflammation, its causes, symptoms, and its relationship to the immune system, and examine its components and influences in the body, the relationship between histamine and cytokines, and the short- and long-term consequences that can result from inflammation. Updated: 09/19/2021

Bee Sting Reactions

Picture a nice summer day at the beach. All is well. The sun is out, the breeze is cooling you off and the water is crystal clear. Then you get stung by a bee, and everything goes haywire. Now your day is ruined. At best, you'll have some local pain near where the bee stung you. At worst, you could die. That is all thanks to a very important part of your innate immune system.

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  • 0:31 Inflammation
  • 2:01 Histamine and Cytokines
  • 3:49 When Inflammation Goes Wild
  • 6:07 Lesson Summary
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This part is called inflammation, and it is a series of defensive biological reactions to harmful agents that leads to pain, redness, swelling and heat in the affected areas of the body. More technically, you may hear that inflammation leads to several cardinal signs called:

  • Dolor, or pain
  • Calor, which means heat
  • Rubor, or redness
  • Tumor, which implies a swelling of sorts
  • Functio laesa, or loss of function

All of this shouldn't really come as a big shocker to you. Picture this: the bee landed on your arm and stung you. The physical action of the sting slicing through your tissues sets off nerves that signal pain to your brain. The venom that comes with the stinger is recognized as a foreign substance and sets off a chain of reactions that result in increased flow, or red, hot blood, to the area, and the release of many different molecules by your body's cells.

Some of the molecules released by nearby cells cause additional pain, while others help to create leaky blood vessels. This leakiness of blood vessels leads to the swelling of surrounding tissue and all of these components may, in one way, shape or form, lead to the loss of function of an area affected by inflammation.

Histamine and Cytokines

This terrible-sounding process isn't warrantless. In fact, the tissues, cells and chemicals secreted by the cells that lead to inflammation are very important. For example, if a little bacteria were to invade your body through a little crack in the skin, your innate immune system would launch the same exact inflammatory response as it would have to a bee sting. That's because the inflammatory process is non-specific; it goes after anything and everything in virtually the same way. Remember that point for just a little while later.

As this little bacteria sneaks into the crack in the skin, your body's cells recognize that there is a foreign invader that shouldn't be there. They release all sorts of chemicals, notably histamine, that cause the blood vessels in the area to become leaky.

This leakiness is super important as it allows for important cells (white blood cells) normally unable to pass through the vessel walls to waltz into the affected tissue, where they can kill the bacteria. If they can't kill the bacteria, they can release molecules used for signaling, called cytokines, to attract bigger or stronger cells to kill the bacteria for them.

Besides white blood cells, the permeability of the vessels, namely capillaries, also allows for fluids to leak into the area. This fluid contains all sorts of proteins, enzymes and other goodies that can help to kill the foreign invader as well.

As this fluid leaks in, the swelling increases, and this in turn causes pressure in the tissues to build up. As the pressure builds up, it compresses everything, including nerve receptors in the area of the swelling. This compression of nerves causes additional pain signals to be sent to your brain.

When Inflammation Goes Wild

This brings me to my next important point. I told you to remember that the inflammatory process is non-specific. This means it goes after everything, and I mean everything. The molecules released during the inflammatory process not only kill bacteria but end up hurting your own body's cells as well, which causes you that pain.

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