A peptide hormone produced
in the S cells of the duodenum. Secretin
is released in response to low duodenal pH caused
by the presence of hydrochloric acid
from the stomach, and stimulates the secretion
of bile from the liver,
alkaline pancreatic juice from the pancreas,
and biocarbonate from duodenal Brunner's glands. It also reduces acid secretion
from the stomach by inhibiting gastrin release
from G cells. The result of these actions is to help neutralize the pH of
the digestive products entering the duodenum from the stomach, which is
important as enzymes from the pancreas (e.g. pancreatic amylase
and pancreatic lipase) function optimally at neutral pH.
| Secretin molecule. Source: PubChem
Secretin, whose function was first demonstrated in 1902, was the first substance
to be described as a hormone.