What is metaplasia?

• A. Increase in tissue mass
• B. Abnormal changes in cell organization
• C. Conversion of one mature cell type into another
• D. Decrease in cell size

Answer: (C)

Metaplasia is defined as the conversion of one mature cell type into another mature cell type, often as an adaptive response to chronic irritation or inflammation. This process typically involves the transformation of one type of epithelial cell to another type that may be more suited to withstand environmental stressors. For instance, in response to cigarette smoke, the normal ciliated columnar epithelium of the respiratory tract can be replaced with stratified squamous epithelium. This change can help protect against damage from inhalants but may also lead to a decrease in the function of the respiratory epithelium’s ability to clear mucus and pathogens.

This process is distinct from other options: an increase in tissue mass describes hyperplasia; abnormal changes in cell organization are indicative of dysplasia; and a decrease in cell size refers to atrophy. Metaplasia does not imply an increase or decrease in the number of cells or their organization but rather a change in the type of mature cells present. Understanding metaplasia is crucial as it can serve as a precursor to more serious conditions, including neoplasia, under prolonged irritating influences.