This slide shows a cross section of the duodenum (a portion of the small intestine)Note that the intestinal villi (finger-like projections) are lined with  simple columnar epithelium.  Interspersed among these columnar cells are goblet cells that secrete mucus that coats the lumen of the intestine.  During routine histological preparation the mucus is lost, leaving a clear or lightly stained cytoplasm.