Ultrastructure of surface epithelial cells of the normal human rectum.

Luminal surface epithelial cells, excluding a few endocrine cells of the normal human rectum, were studied electron microscopically and 5 types of cells were recognized with special reference to some structure containing mucous substances. Principal-1 cells showing few tiny vesicles and Principal-2 cells containing some tiny vesicles seemed to belong to the absorptive cell group. Vesicle cells having numerous tiny vesicles, and Columnar mucous cells accompanied by numerous tiny vesicles and some round or oval mucous vacuoles, seemed to be labelled as of the secretory cell group. The common features of the epithelial columnar cells, except for the Goblet cell, were columnar shape, microvilli whose length and density had considerable variation, glycocalyceal bodies around the microvilli, and thick surface coat. Goblet cells were characterized by a goblet shape which was expanded by numerous mucous droplets. It is of special interest that 4 different types of columnar epithelial cells are recognized on the luminal surface of the normal human rectum, and that Vesicle cells and Columnar mucous cells are first observed on the luminal surface of the large intestine. Similar epithelial cells have only been reported in the crypt of the large intestine and not on the luminal surface.