The upper gastrointestinal tract consists of oesophagus, stomach, and duodenum. These are distinct from one another histologically. The lining of the oesophagus consists mainly of non-keratinising stratified squamous epithelium, and there is a variable amount of columnar epithelium distally. The stomach has three main histological regions, which from proximal to distal are the cardia, the body/fundus, and the antrum. All of these regions include surface epithelial cells that extend downwards into foveolae. Beneath the foveolae are a short isthmic zone and a deeper glandular layer. In the body/fundus, the glandular layer is thicker and the glands are more closely packed than in the antrum. Parietal cells and chief cells are the main component of the body/fundus glands while in the antrum they are sparse. The gastric cardia is a short segment that usually lacks parietal and chief cells. In the normal state, columnar mucosa extends from the stomach upwards into the distal oesophagus for a variable length. In contrast, Barrett’s oesophagus is pathological replacement of the distal oesophageal mucosa by metaplastic columnar mucosa that may be gastric or intestinal. The duodenal mucosa includes villi and crypts, both lined by columnar absorptive cells. Other epithelial cell types include goblet cells and Paneth cells. Endocrine cells are present at all sites but are difficult to identify and sparse in the oesophagus.