The Inflammatory Response: Definition & Steps

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  • 0:00 Inflamation
  • 0:31 Inflammaory Triggers
  • 1:07 Steps
  • 2:44 Goals
  • 3:28 Chronic Inflammation
  • 3:58 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

The inflammatory response is a part of your innate immune system that responds to infection and injury. In this video, you'll learn about the process of inflammation and what happens when it becomes chronic.


It's happened to all of us. You are walking alone, and suddenly you step in a hole or off of a curb and your ankle twists. Immediately, you feel pain. Soon, your ankle starts to swell and turn red, and it might even feel hot to the touch. What's going on inside your ankle that's making all these things happen? It's called inflammation, and it's an important way that your body repairs damage and fights off infection.

Inflammation Triggers

What triggers inflammation in your body? The inflammatory process is part of the innate immune system, which means that it is nonspecific and responds to many types of potential threats. Any damage to your tissues can trigger inflammation. Sometimes, this occurs because your body has been invaded by bacteria or viruses, but other times, inflammation is triggered by damage to tissues inside your body. When you sprained your ankle, the connective tissues and muscles were torn. This tissue damage causes the release of inflammatory molecules that begin the inflammatory process.


When tissues are damaged by infection or injury, they release inflammatory molecules called cytokines. Cytokines are a very important part of the inflammatory process, and they have several effects on the cells around them.

At the beginning of the inflammatory response, small blood vessels called arterioles dilate and become leakier. This brings more blood into the affected area. Other cytokines attract white blood cells called neutrophils, and the leaky arterioles make it much easier for them to move quickly out of your blood vessels and into the tissues where they can start fighting infection and repairing tissue damage. Of course, as blood vessels dilate and become leaky to allow cells out, a lot of fluid leaks out too, causing redness and swelling. As the swelling increases, the area becomes more and more painful as neighboring tissues are squeezed, triggering pain and pressure receptors.

Cytokines called pyrogens are also released to raise the temperature of the affected area. Sometimes, your entire body temperature may go up, and you may develop a fever, depending on the severity of the infection or injury.

By now, you would be experiencing all of the classic symptoms of inflammation, as denoted by their Latin words and their meanings: calor (heat), dolor (pain), rubor (redness), and tumor (swelling). These signs of inflammation were first described by physicians over 2000 years ago, and we still use them today to identify an acute inflammatory response.

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