From the perspective of function, the contents of the gut lumen lie outside the body and contain a toxic/antigenic load from which the body needs to be protected. Protection is supplied by complex mechanisms which support one another: intestinal secretions (primarily mucus and secretory IgA), the mucosal epithelium, and intramural lymphocytes. This primary, intestinal barrier is supported by the liver, through which all enterically-derived substances must pass before entering the arterial circulation for transport to other tissues and organs. Kupffer cells in the hepatic sinusoids remove absorbed macromolecules by phagocytosis. Hepatic microsomal enzymes alter gut-derived chemical substrates by oxidation and by conjugation to glycine and glutathione(GSH) for excretion into bile and for circulation to the kidneys. The cost of detoxification is high; reactive intermediates and free radicals are generated and anti-oxidants like GSH are consumed. Any compromise of intestinal barrier function increases the production of oxygen radicals and carcinogens by the liver’s cytochrome P-450 mixed-function oxidase system. The excretion of oxidation by-products into bile and the reflux of this “toxic” bile into the pancreatic ducts may be the major cause of chronic pancreatic disease.