The surface topography of the colonic crypt in rabbit and monkey

Scanning electron microscopy (SEM) was used to investigate the epithelial topography of the surface and crypt in rabbit and monkey colon. Crypt openings in monkey colon are arranged in a hexagonal pattern, in sharp contrast to rabbit colon where they are randomly arrayed and frequently hidden by epithelial folds. Crypt lumens were exposed by freezing ethanol-dehydrated tissue in liquid nitrogen and fracturing the tissue with a razor blade. The resulting overview of crypt-cell luminal surfaces showed that as columnar cells mature and migrate up the crypt and onto the colonic surface, their microvilli become progressively more abundant. Goblet cells were readily identified in the cross-fractured crypt epithelium; their luminal surfaces are characterized by short, sparse microvilli. The changing appearance of the luminal surface of goblet cells was visualized by SEM during the exocytosis of single mucous granules from unstimulated crypt goblet cells, and during the compound exocytosis of multiple granules in response to acetylcholine.