Page 175 - The Cell in 40 Topics

igested foods reaching the intestine from the stomach con-
tain powerful acids, which constitute a grave danger for the
duodenum—because unlike the stomach, the duodenum has
no special lining with which to protect itself.
How is it, therefore, that these acids leave the duodenum unharmed?
When we look at the events taking place during digestion in order to an-
swer that question, we encounter miraculous phenomena occurring in the
body.
When the amount of acid reaching the duodenum from the stomach
together with foodstuffs reaches danger levels, the intestine begins secret-
ing a hormone called secretin from the cells in its walls. In the small intes-
tine, this secretin that protects the duodenum exists in the form of
prosecretin. But under the influence of acidic digested foods, this hormone
transforms into secretin, a different chemical substance (Figures 141 and
142).
The hormone secretin enters the bloodstream and reaches the pan-
creas, where it asks the pancreas to secrete enzymes. Learning—by means
of the secretin—that the duodenum is in danger, the pancreas sends bicar-

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