"The function of the lining of that tube is to break those substances down into particles that are so simple that, when absorbed, they can no longer be identified by our immune system as having come from something outside our body."
this reallypaints a clear picture of what the body is up against, if the lining isn't functional...and of course, there are so mnay ways we have to destroy it's integrity thse days.
Rampant Antibiotic use comes to mind as among the great evils of modernity.