Secretin is a
peptide hormoneproduced in the S cells of the duodenumin the crypts of Lieberkühn. Its primary effect is to regulate the pHof the duodenal contents via the control of gastric acidsecretion and buffering with bicarbonate. It was the first hormone to be discovered (see below).
Secretin is secreted in response to low duodenal pH due to
chyme, which contains hydrochloric acid, entering from the stomach. It is the active form of prosecretin.
Secretin stimulates the secretion of
bicarbonate(base) (bile) from the liver, watery bicarbonate solution from pancreatic duct epithelium, and duodenal Brunner's glands in order to buffer the incoming protonsof the acidic chyme [Guyton, Hall. Textbook of Medical Physiology 11edt. Elsevier, 2006. pp 800-801] . It also enhances the effects of cholecystokinin. It is known to promote the normal growth and maintenance of the pancreas.
blood glucoseconcentration spikes by triggering increased insulinrelease, following oral glucoseintake. [cite journal |author=Kraegen EW, Chisholm DJ, Young JD, Lazarus L |title=The gastrointestinal stimulus to insulin release. II. A dual action of secretin |journal=J. Clin. Invest. |volume=49 |issue=3 |pages=524–9 |year=1970 |pmid=5415678 |doi=10.1172/JCI106262 [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=322500 Free Full Text] ]
It also reduces acid secretion from the
stomachby inhibiting gastrinrelease from G cells. This helps neutralize the pH of the digestive products entering the duodenum from the stomach, as digestive enzymes from the pancreas (eg, pancreatic amylaseand pancreatic lipase) function optimally at neutral pH.
Secretin is a
peptide hormone, composed of 27 amino acids, of which 14 amino acids are homologousto the sequence of glucagon.
William Baylissand Ernest Starlingwere studying how the nervous system controls the process of digestion. It was known that the pancreas secreted digestive juices in response to the passage of food into the duodenum. They discovered (by cutting all the nerves to the pancreas in their experimental animals) that this process was not, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion "secretin". Secretin was the first such "chemical messenger" identified. This type of substance is now called a " hormone", a term coined by Bayliss in 1905.
* [http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/gi/secretin.html Overview at colostate.edu]
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