Secretin is a peptide hormone. It is formed in the small intestine and serves to neutralize the chyme.
What is secretin?
Secretin is a hormone that is chemically a peptide and belongs to the glucagon family of peptide hormones. It is made up of several amino acids and has hydrophilic properties.
That means it is soluble in water. The hormone is formed in the small intestine when the chyme with a pH value below 3.5 is passed from the stomach into the small intestine. Secretin is released into the blood of the portal vein and thus reaches the other organs of the digestive tract. The main target organ is the pancreas, which releases bicarbonates as a result.
Function, effect & tasks
The main place of action of the secretin are other digestive organs. The hormone reaches this via the bloodstream. In the pancreas, gall bladder and small intestine, secretin leads to an increased production of sodium hydrogen carbonate (NaHCO3).
Sodium hydrogen carbonate is also known as baking soda and has the ability to neutralize acids. In healthy people, secretin also inhibits the secretion of the hormone gastrin. Gastrin is a polypeptide and is produced in the stomach and small intestine. Among other things, it stimulates the production of hydrochloric acid in the stomach. However, if a person suffers from gastrinoma, secretin stimulates gastrin secretion. This is of course rather counterproductive, since the secretin is supposed to raise the pH value in the small intestine. Secretin also causes the gallbladder to contract. This then releases the stored bile into the small intestine.The bile has a pH of 8.0 to 8.5 and is therefore basic.
The hormone secretin also stimulates the mucous membrane cells of the stomach to produce mucins. Mucins are slimy substances. On the one hand, they protect the mucous membrane of the small intestine, on the other hand, they delay gastric emptying. This prevents even more acidic chyme from getting into the small intestine.
The release of insulin and somatostatin is also stimulated by secretin. Insulin is a hormone made in the pancreas. It pushes the glucose that circulates in the blood into the cells. Somatostatin is also made in the pancreas. The hypothalamus also produces somatostatin. The hormone works as a kind of "brake". Among other things, it inhibits the release of numerous digestive hormones.
Education, occurrence, properties & optimal values
Secretin is a gastrointestinal hormone. It is formed in the duodenum and jejunum. The duodenum and jejunum are two sections of the small intestine. More precisely, the hormone is produced in the S cells. The stimulus for secretion is a low pH value of the chyme in the small intestine.
The pH value must be below 4.5. There are no optimal values for the hormone, as it is always released depending on the food consumed. The function of the pancreas can be checked by administering secretin. If secretin is administered to a healthy person, the pancreas would have to secrete more bicarbonate-containing secretions. If this does not happen, there may be pancreatic insufficiency.
Diseases & Disorders
Secretin plays an important role in Zollinger-Ellison syndrome. This syndrome is a paraneoplastic disease. Paraneoplastic syndromes occur as accompanying symptoms in various types of cancer.
The causative tumors in Zolliner-Ellison syndrome are mainly found in the pancreas and the small intestine. In more than 50% of the cases they are malignant. The tumors produce the hormone gastrin. That is why they are also called gastrinomas. The overproduction of gastrin leads to an overproduction of stomach acid. The increased acid load leads to ulcer formation with abdominal pain, bloody vomiting and diarrhea. Secretin normally inhibits the release of gastrin. In gastrinoma, however, secretin causes excessive gastrin secretion. A secretin provocation test can therefore also be carried out to detect Zollinger-Ellison syndrome.
In this test, blood is first drawn from the patient so that the gastrin level can be measured before the test. Secretin is then injected into the patient's vein. Further blood samples are taken at intervals of 2, 5, 10 and 30 minutes, starting from the first blood sample. If an increase in the gastric concentration in the serum of more than 100% can be determined in these blood samples, this is considered to be evidence of the presence of Zollinger-Ellison syndrome.
In recent years, secretin has also caused a stir in autism research. Early childhood autism is a profound developmental disorder. The disease usually manifests itself before the age of three. Typical symptoms of the disorder are a lack of or impaired language development and impaired social interaction. Stereotypical and repetitive behavior are also observed. Exact causes are not yet known, but genetic factors seem to play a role. Since the causes are not yet known, there is no causal therapy. Most affected children are treated with neuroleptics or serotonin reuptake inhibitors (SSRI preparations).
At the beginning of 2000, however, a study from the USA caused a stir. In this study, three children were given the hormone secretin intravenously. Within five weeks of this single dose, the children's social behavior improved. Since this publication, especially in the USA, children with autism have been treated with secretin. Parents of the treated children speak of a noticeable improvement in more than 75%. The children are more attentive and the linguistic communication skills have also improved significantly. However, 30% of the parents also reported negative reactions such as hyperactivity or increased aggression.
