Clinical Considerations: Metaplasia and Epithelial Tumors
- Metaplasia is conversion of one differentiated epithelial type into another in response to persistent injury.
- Persistent injury can trigger epithelial adaptation when the original epithelial type is poorly suited to chronic stress.
- Differentiated epithelium means mature epithelium with specialized features.
- Glandular epithelium can transform into squamous epithelium in some metaplastic responses.
- Chronic acid reflux exposes the lower esophagus to stomach acid and pepsin over time.
- Pepsin is a stomach enzyme that digests proteins and can injure esophageal lining when reflux is chronic.
- Stratified squamous nonkeratinized epithelium normally lines the esophagus.
- Barrett epithelium is glandular mucus-secreting epithelium that can replace normal lower-esophageal squamous epithelium during chronic reflux.
- Gastric cardia is the stomach region near the esophagus, and Barrett epithelium can resemble mucus-secreting epithelium from this region.
- Mucus-secreting change helps protect the esophagus from acid and pepsin but creates a clinically important abnormal lining.
- Esophageal adenocarcinoma risk increases because Barrett epithelium is a recognized precursor lesion.
- Epithelial-cell tumors arise when epithelial cells fail to respond properly to normal growth-regulatory mechanisms.
- Growth-regulatory mechanisms are signals that normally control when cells divide, stop dividing, repair, or die.
- Benign tumors remain localized and do not invade neighboring tissues.
- Malignant tumors invade neighboring tissues and may metastasize.
- Metastasis means tumor spread from the original site to distant sites.
- Carcinomas are malignant tumors that arise from surface epithelia.
- Adenocarcinomas are malignant tumors that arise from glandular epithelium.
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