What is secretin?
Secretin is a hormone that is chemically a peptide and belongs to the glucagon family of peptide hormones. It is composed of several amino acids and has hydrophilic properties.
This means that it is soluble in water. The hormone is formed in the small intestine when the chyme, with a ph of less than 3.5, is channeled 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. Target organ is mainly the pancreas, which releases bicarbonates as a result.
Function, effect & tasks
The main active site of the secretin are other digestive organs. This reaches the hormone via the bloodstream. In pancreas, gall bladder and small intestine secretin leads to increased production of sodium bicarbonate (NaHCO3).
Sodium bicarbonate is also known as soda and has the ability to neutralize acids. In healthy humans, secretin also inhibits the secretion of the hormone gastrin. Gastrin is a polypeptide and is produced in the stomach and small intestine. It stimulates, among other things, the production of hydrochloric acid in the stomach. However, if a human is suffering from a gastrinoma, secretin stimulates gastrin secretion. Of course, this is rather counterproductive because the secretin is supposed to raise the pH in the small intestine. Secretin also causes a contraction of the gallbladder. This then returns 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. Muzins are mucilages. On the one hand they protect the mucous membrane of the small intestine, on the other hand they delay the gastric emptying in the stomach. This prevents even more sour chyme from getting into the small intestine.
The secretion of insulin and somatostatin is also stimulated by secretin. Insulin is a hormone that is made in the pancreas. It injects the glucose circulating in the blood into the cells. Somatostatin is also produced in the pancreas. The hypothalamus also produces somatostatin. The hormone works as a kind of "brake". Among other things, it inhibits the secretion of many digestive hormones.
Education, occurrence, properties & optimal values
Secretin is a gastrointestinal hormone. It is formed in the duodenum and jejunum. Duodenum and jejunum are two sections of the small intestine. More specifically, the hormone is produced in the S cells. The stimulus for secretion is a low pH of the chyme in the small intestine.
The pH must be below 4.5. There are no optimal values for the hormone, as it is always released depending on the food consumed. By administering secretin, however, the function of the pancreas can be checked. If a healthy secretin is administered, the pancreas would have to release more bicarbonate-containing secretions. If this does not happen, there may be pancreatic insufficiency.
Diseases & Disorders
Secretin plays an important role in the clinical picture of Zollinger-Ellison syndrome. This syndrome is a paraneoplastic disease. Paraneoplastic syndromes appear as concomitant symptoms in different cancers.
The causative tumors are found in Zollin-Ellison syndrome mainly in the pancreas and small intestine. In more than 50% of 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 gastric acid. The increased acidity leads to ulceration with abdominal pain, bloody vomiting and diarrhea. Normally secretin inhibits the secretion of gastrin. In the gastrinoma, on the other hand, secretin causes excess gastrin secretion. To prove a Zollinger-Ellison syndrome, therefore, a secretin provocation test can also be performed.
In this test, the patient is first bled so that the gastrin level can be measured before the test. Secretin is then injected into the vein of the patient. At intervals of 2, 5, 10 and 30 minutes, starting from the first blood sample, further blood samples are taken. If an increase in serum gastrin concentration by more than 100% can be detected in these blood samples, this is considered evidence of the presence of Zollinger-Ellison syndrome.
In recent years, secretin has also caused more and more attention in autism research. Early childhood autism is a profound developmental disorder. Mostly, the disease manifests before the third year of life. Typical symptoms of the disorder include a lack of or disturbed speech development and a limitation of social interaction. Also stereotypical and repetitive behavior are 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 of the 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 sensation. In this study, the hormone secretin was given intravenously to three children. Within five weeks of this one-time dose, the children's social behavior improved. Since this publication, children with autism are treated with secretin especially in the US. Parents of the treated children speak in more than 75% of a noticeable improvement. The children are more attentive and the linguistic ability to communicate has improved significantly. However, 30% of parents also reported negative reactions such as hyperactivity or increased aggression.