metaplasie

Metaplasia, or metaplasie, is a reversible change in which one mature cell type is replaced by another mature cell type that is better suited to a new local environment. It is an adaptive process and distinct from hyperplasia, dysplasia, and neoplasia. Metaplasia occurs in response to chronic irritation, inflammatory signals, hormonal shifts, or tissue injury, and may be reversed if the inciting factor is removed, though ongoing damage can increase the risk of dysplasia or cancer in some tissues.

The most common forms are squamous metaplasia and intestinal metaplasia. Squamous metaplasia replaces a columnar or glandular epithelium with a stratified squamous epithelium, often seen in the respiratory tract of smokers or patients with chronic bronchitis. Intestinal metaplasia replaces epithelium with intestinal-type epithelium containing goblet cells, as in Barrett's esophagus, where esophageal squamous mucosa changes to intestinal-type mucosa due to chronic gastroesophageal reflux. Gastric intestinal metaplasia arises from chronic gastritis and Helicobacter pylori infection. Metaplasia can also occur outside epithelia, including osseous or cartilaginous metaplasia in soft tissues during chronic inflammation or after injury.

Mechanistically, metaplasia is thought to involve reprogramming of resident stem or progenitor cells or transdifferentiation of mature cells, driven by signaling pathways and epigenetic changes in response to the new environment. It is typically diagnosed histologically by tissue biopsy. Clinical significance varies by site; Barrett's esophagus carries a higher risk of adenocarcinoma, while other metaplastic changes may be benign if the irritant is removed.