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Secretin is a hormone produced in the duodenum which plays an important role in the digestive process and also appears to be involved in osmoregulation, the process the body uses to keep the internal balance of salt and fluids stable. This hormone can also be introduced into the body, usually in a test which is designed to check on the function of the pancreas. Secretion for injection or introduction to the body through a gastric tube is available from several pharmaceutical companies, by prescription only.
A cascading series of reactions happen when people start to digest food. Secretin is one of the many players involved. As food moves through the stomach, it transitions into a partially digested state known as chyme. Chyme is very acidic as a result of the gastric juices it has been marinating in, and when it starts to be pushed into the intestines, secretin kicks into action.
One of the things secretin does is trigger the production of bicarbonates which are used to neutralize the acid in the chyme so that it does not damage the intestines. Unlike the stomach, the intestines are not equipped to deal with the harsh gastric juices used in the early stages of digestion. The release of secretin also tells the stomach to stop making gastric juices, indicating that the next phase of digestion is beginning and that the stomach can take a break.
Secretin also triggers the production of pancreatic juices and liver bile, which are used to lubricate the chyme as it moves through the digestive tract. Additionally, if the glucose content of the food is high, secretin will also stimulate the production of insulin to handle the glucose.
In the secretion stimulation test, a patient will be injected with secretin to see how the pancreas responds. If stimulation with this hormone does not result in the production of pancreatic juices, it indicates that the patient has a medical issue which needs to be identified and treated. This test can be uncomfortable, as the secretin is often introduced through a stomach tube, and many people gag during the placement and removal of the tube.
This hormone has another distinction: It was the first hormone identified. Researchers working with the digestive tract in the early 1900s noted that this compound appeared to play an important role, sending chemical signals to moderate the digestive process. This contradicted the expectation that the digestive process was mediated by the nervous system, changing the way that scientists thought about the body and paving the way to the discovery of other “chemical messengers,” which came to be called hormones.