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Metaplasia is a benign process where one cell type changes into another due to pathological or physiological stress. Common types include changes from squamous cells to glandular cells or vice versa, and changes from one glandular cell type to another. Barrett’s esophagus, a type of metaplasia, involves the replacement of squamous cells with glandular cells in the lower end of the esophagus due to gastroesophageal reflux disease (GERD), and increases the risk of esophageal cancer. Other types of metaplasia occur in the bronchi, vagina, stomach, small intestine, and bladder.
Metaplasia, a benign process that causes one cell type to change into another, comes in many forms. The most common varieties involve changes from squamous cells to glandular cells or vice versa. Another variety involves changes from one glandular cell type to another. A rarer type affects transition cells, which is a cell type unique to the urinary tract. Metaplasia usually occurs due to pathological or physiological stress in different parts of the body.
A common type of metaplasia is called Barrett’s esophagus, a process involving the cells lining the lower end of the esophagus. Normally, the part of the esophagus immediately above the stomach is lined with squamous cells, which are flat, compressed cells that protect deeper structures from damage. If a patient has a condition called gastroesophageal reflux disease (GERD), hard stomach acid backs up into the esophagus and damages squamous epithelial cells. Due to the pathological stress on the esophagus, the squamous cells are replaced by glandular cells, a different type of cell. While this is a benign change, patients with this condition have a higher risk of developing esophageal cancer in the future.
Another type of metaplasia involves a change in cell type from glandular cells to squamous cells, which is the opposite of what happens with Barrett’s esophagus. This process takes place in the bronchi, which are the tubes that carry air from the trachea to distant parts of the lung. Usually these bronchi are lined with glandular cells, which help produce secretions that trap inhaled particles and protect other parts of the lung from blockage. In patients exposed to cigarette smoke or other environmental toxins, glandular cells are replaced by squamous cells. This reduces the lung’s defenses against inhaled irritants.
Glandular cell to squamous cell metaplasia can also occur in the vagina. Typically, the vagina is lined with squamous cells, but this lining changes into glandular cells at the beginning of the cervix. This transition point between squamous and glandular cells changes throughout women’s lives and throughout their menstrual cycles. This metaplastic process is considered a benign change that has no major repercussions.
Another type of metaplasia involves transformations from one glandular cell type to another glandular cell type. The stomach and small intestine are lined with glandular cells. Because the environments are different within these parts of the gastrointestinal tract, especially because the contents of the stomach are much more acidic than that of the intestines, different glandular cells are needed to protect the underlying structures from damage. When there is inflammation of the stomach, a condition known as gastritis, a part of the intestine near the stomach may have a change in the type of gland cells present.
A rare type of this condition affects the bladder, which is normally lined with a type of cell called transition cells. With chronic irritation of the bladder, such as with infection, this transient cell lining changes to a scaly lining. This process is benign, but can put a patient at risk for a malignant tumor called squamous cell carcinoma of the bladder.
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