Metaplasia is a biological process where one type of mature cell transforms into another type of mature cell. This change often occurs in response to chronic irritation or inflammation, allowing the tissue to adapt to new conditions. For example, in the respiratory tract, ciliated columnar epithelial cells may change to squamous epithelial cells when exposed to smoke or other irritants. While metaplasia can be a protective mechanism, it may also lead to complications. If the underlying cause of irritation persists, the altered cells can become dysfunctional or even progress to dysplasia, which is a precursor to cancer.