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Villi Damage
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The villi are the most important part of the absorptive system in the
small intestine.  Normal villi are long and slender, giving a healthy
small intestine the appearance of a deep pile carpet.  All these villi
give the small intestine an enormous absorptive surface; if laid out
flat it would cover an area the size of a tennis court.
 
Now consider the "worst case" scenario for CD, where the villi are
completely flattened.  This decreases the absorptive surface down from
a tennis court to about the size of a small table.  So you have a
dramatic reduction in the amount of area for digesting and absorbing
nutrition from your food.  But there are other factors to consider as
well.  The villi aren't just flattened, they are also inflamed; just
like your skin is inflamed after being burned.  It can produce pain.
(But the pain is not as obvious and localized as it is for inflamed
skin; you just know that there is pain in there somewhere.)
 
Often the villi are not completely flat.  Dr. Murray showed a slide
in which the villi were a little "stubby".  In these cases the villi
are still different enough to be classified as not fully formed.  But
then he showed a slide in which the villi appeared to be normal size.
Many pathologists would look at such a case and be tempted to rule out
CD as a possibility.  However, if you carefully examine the surface of
the villi you'll see that there is a marked increase in lymphocytes,
the small immune cells that reside in the intestine.  It is the
lymphocytes which are mostly responsible for the damage in the small
intestine.  These are the cells that are responding to gluten.
 
Dr. Murray talked about five degrees of severity of villi damage:
 
  1. Healthy, undamaged villi.
 
  2. Infiltrated villi.  The villi are still standing up long and
     straight, but the is an increase in the surface lymphocytes.
 
  3. Partially-shortened villi.  The villi are somewhat short and
     stubby, and the crypts (the basement parts of the villi) are
     expanding and becoming inflamed.
 
  4. Flattened villi.  This is the typical or classic form of CD, in
     which the villi are destroyed.
 
  5. Burned-out villi.  This can occur in older celiacs, where the
     villi don't necessarily have the ability to recover on a GF diet.