About one to two hours after eating some food, the partially digested
food is then moved to the duodenum (start of the small intestine).
When the food reaches the duodenum, two hormones are released into the
bloodstream to signal the pancreas. These are secretin and
cholecystokinin (CCK). Secretin is used as a signal to tell the
pancreatic duct cells (which are about 15% of the pancreas) to release
bicarbonate (HCO3-) into the duodenum to raise its pH, since it is
very acidic from the stomach acids. The CCK is used as a signal to
tell the pancreas to release enzymes to the small intestine, in order
to absorb the food into the bloodstream. The enzymes, however, become
denatured (deactivated) if the pH does not rise above a certain level.
So why does the pancreas fail to do its job in CF? With a defective
CFTR protein, HCO3- is not released in adequate amounts to act as an
effective buffer to neutralize the stomach acid so that the enzymes
can absorb the food. Also the lack of HCO3- can create mucus plugs,
which will then limit the amount of enzymes that can reach to intestines.