Secretin is a peptide hormone. It is produced in the small intestine and is used to neutralize the food pulp.
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 food pulp with a ph of less than 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 target organ is primarily the pancreas, which secretes bicarbonates as a result.
Function, action, and tasks
The main site of action of the secretin is other digestive organs. The hormone reaches these via the bloodstream. In the pancreas, gallbladder, and small intestine, secretin leads to increased production of sodium bicarbonate (NaHCO3). Sodium hydrogen carbonate is also known as baking 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. 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 secretin is supposed to raise the pH in the small intestine. Secretin also causes contraction of the gallbladder. This then releases the stored bile into the small intestine. Bile has a pH of 8.0 to 8.5 and is therefore alkaline. The hormone secretin also stimulates the mucosal cells of the stomach to produce mucins. Mucins are mucous substances. On the one hand, they protect the mucous membrane of the small intestine, and on the other hand, they delay gastric emptying in the stomach. This prevents even more acidic food pulp from entering the small intestine. The secretion of insulin and somatostatin is also stimulated by secretin. Insulin is a hormone produced in the pancreas. It carries glucose circulating in the blood into the cells. Somatostatin is also produced in the pancreas. The hypothalamus also produces somatostatin. The hormone functions as a kind of “brake.” Among other things, it inhibits the release of numerous digestive hormones.
Formation, occurrence, properties, and optimal levels
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 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 value must be below 4.5. There are no optimal values for the hormone, as it is always secreted depending on the food ingested. However, the function of the pancreas can be checked by administering secretin. If secretin is administered to a healthy person, the pancreas should secrete more bicarbonate-containing secretion. If this does not occur, pancreatic insufficiency may be present.
Diseases and disorders
Secretin plays an important role in the clinical picture of Zollinger-Ellison syndrome. This syndrome is a paraneoplastic disorder. Paraneoplastic syndromes occur as concomitant symptoms of various cancers. In Zolliner-Ellison syndrome, the causative tumors are mainly found 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 results in an overproduction of stomach acid. The increased acid load leads to ulceration with abdominal pain, bloody vomiting and diarrhea. Normally, secretin inhibits the secretion of gastrin. In gastrinoma, however, secretin causes excessive gastrin secretion. Therefore, a secretin provocation test can also be performed 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. At intervals of 2, 5, 10 and 30 minutes, starting from the first blood draw, additional blood samples are taken. If an increase of more than 100% in the serum gastrin concentration can be detected in these blood samples, this is considered evidence of the presence of Zollinger-Ellison syndrome.In recent years, Sekretin has also attracted increasing attention in autism research. Early childhood autism is a profound developmental disorder. In most cases, the disorder manifests before the age of three. Typical symptoms of the disorder are absent or impaired language development and a restriction of social interaction. Stereotypic and repetitive behavior are also observed. Exact causes are currently unknown, but genetic factors appear to play a role. Since the causes are not yet known, there is also no causal therapy. Mostly, the affected children are treated with neuroleptics or serotonin reuptake inhibitors (SSRI drugs). At the beginning of 2000, however, a study from the USA caused a sensation. In this study, the hormone secretin was administered intravenously to three children. Within five weeks of this single dose, the children’s social behavior improved. Since this publication, children with autism have been treated with secretin, particularly in the USA. Parents of the treated children report a noticeable improvement in more than 75%. The children were said to be more attentive and their ability to communicate in speech had also improved significantly. However, 30% of parents also reported negative reactions such as hyperactivity or increased aggression.
