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Metaplasia: Definition, Symptoms & Examples

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  • 0:03 What Is Metaplasia?
  • 0:38 What Is Affected?
  • 1:17 Smoking Induced Metaplasia
  • 2:24 Stomach Acid Induced…
  • 3:16 Metaplasia in the Bladder
  • 3:50 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
In this lesson, learn how cell tissue can transform from one shape to another under certain conditions, called metaplasia. Learn where this might occur, for what reasons, and some signs and symptoms people may experience as a result.

What Is Metaplasia?

Have you heard of Dr. Jekyll and Mr. Hyde? Dr. Jekyll sometimes transformed into a different, darker version of himself, that of Mr. Hyde, and back again. Different tissues in your body can also transform and be replaced by totally different looking tissues when stimulated to do so. And, once the stimulus for the transformation is taken away, the change is reversible, much like for Dr. Jekyll and Mr. Hyde. This process is called metaplasia.

Let's go over some examples of this process and their accompanying signs and symptoms.

What Is Affected?

Metaplasia affects epithelial cells. An epithelium is a cellular cover that envelops the outer and inner surfaces of the body, including organs, blood vessels, body cavities, and so on. It's like an external car cover or an inner liner for a truck. Metaplasia often affects the epithelial layers and changes their cell types. There are many types, but the four we will discuss here are:

  • Columnar epithelia, which look like columns
  • Squamous epithelia, which look like single pancakes
  • Stratified squamous epithelia, which look like a stack of pancakes
  • Transitional epithelia, which can contract and expand to change shape

Smoking-Induced Metaplasia

A superb example of metaplasia occurs in smokers. In nonsmokers, part of the surface of their airway is made up of a type of columnar epithelium where the cells look like columns under the microscope. However, in people who smoke for a long time, the toxins act as a stimulus for these cells to be replaced by a different type. The surface turns into a squamous epithelium. Squamous cells are cells that look like single pancakes under the microscope; they're really flat.

On the one hand, having this kind of metaplasia occur is a 'good' thing because it helps better protect the person from the irritants found in the smoke. On the other hand, this squamous epithelium is not only differently shaped, but also devoid of tiny but important hairs that help move pathogenic (or disease-causing) organisms out of the respiratory system. The end result? Smokers are more prone to respiratory infections compared to people who don't smoke, partially as a result of this metaplasia. However, metaplasia is a potentially reversible process. Some smokers can undo the damage their smoking has caused to their respiratory epithelium if they stop smoking!

Stomach Acid Induced Metaplasia

Those of you who have heartburn as a result of reflux esophagitis may have another kind of metaplasia. Reflux esophagitis is a word for the inflammation of the esophagus as a result of stomach acid inappropriately refluxing (or moving up) into the esophagus from the stomach.

The irritation from the stomach acid is the stimulus for the transformation of healthy esophageal epithelium made up of stratified squamous cells (like a stack of pancakes) into a columnar epithelium. By stratified, I mean it's layered. This is a big problem because such a metaplastic change can lead to an adenocarcinoma (a type of cancer) of the esophagus if metaplasia progresses to another kind of cellular change called dysplasia, covered in other lessons.

People with this type of metaplastic change may often have heartburn, trouble swallowing, and even vomiting of blood.

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