<prompt> Barrets esophagus involves most commonly which pa of esophagusUpper 13rdlower 13rdMiddle 13rdDiffuse  <response>: BARRETTS OESOPHAGUS It is the metaplastic changes in the mucosa of the oesophagus as the result of GERD. Squamous epithelium of lower end of the oesophagus is replaced by diseased columnar epithelium columnar metaplasia. There is a macroscopically visible length of columnar mucosa with microscopic features of intestinal metaplasia. It affects lower oesophagus commonly often middle oesophagus also. Ref: SRB;s manual of surgery,3 rd ed , pg no 728 