Intestinal absorption of particulate matter.

Evidence for and against the movement of intact particulates across the normal intestinal mucosa is reviewed. The effects of type of particulate and age of animal are considered. Small particulates unquestionably enter the gut-associated lymphoid tissues of adult animals and are engulfed by macrophages. Published evidence also favors the conclusion that small particulates are taken into absorptive cells of adults by an endocytotic mechanism. The evidence for passage of particulates between intestinal absorptive cells or into villus tips at the extrusion zone is not yet conclusive.