Despite that anatomists consider the cardia as a portion of the stomach, there is disagreement in the literature over whether the cardia mucosa, described as columnar-lined with mucus-producing glands (CLMMG) with or without occasional interspersed oxyntic cells, is part of the stomach, part of the esophagus or a distinct entity. For some authors this mucosa phenotype is a metaplastic glandular change of the distal esophagus caused by protracted gastro-esophageal reflux (GER). In this survey,

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... e presence of CLMMG mucosa was searched for at the esophagus-gastric junction in 50 non-human primates (NHP). The length of the CLMMG (between the squamous epithelium of the esophagus and the first oxyntic fundic gastric gland) was assessed by the aid of an ocular microscale. In all three foetuses, all four stillborn baboons and one 4 day old baboon, the columnar-lined mucosa showed depressions that corresponded to early epithelial pits without glands. In the remaining 45 post-natal NHP, the length of the CLMMG mucosa varied from 0.8 mm to 25.2 mm, and the CLMMG mucosa had replaced the distal esophageal squamous epithelium. The size was neither influenced by the post-natal age nor by the gender of the animals. In NHP, regurgitation with rumination is a natural physiological process leading to GER. The present investigation substantiates the notion that the columnar-lined mucosa with mucus-producing glands is a post-natal developmental process in NHP. These animals seem to offer an excellent spontaneous model to study the series of histological events that take place in the distal esophagus of NHP, most likely under the influence of protracted GER.