What Is Secretin?

The first animal hormone found. Is a basic polypeptide. It consists of 27 amino acid residues and contains 11 different amino acids. Bayliss and Starling were discovered in 1902. Secretin producing cells are "S" cells, mainly in the duodenal mucosa, with a small amount distributed in the jejunum, ileum, and antrum.

Secretin

First discovered

Also known as

Secretin

Regarding the phenomenon of acidic chyme entering the small intestine causing pancreatic juice secretion, as early as 1850, the famous French experiment

Physiologist Claude Bernard discovered it, but it didn't seem to have caught the world's attention. It was later rediscovered by Dolinski, a physiologist at Pavlov's laboratory in Russia. We know that Ivan P. Pavlov is considered to be the founder of modern digestive physiology. His contribution to digestive physiology is very outstanding. He won the Nobel Prize in Physiology or Medicine in 1904 and won world honor. However, because of being bound by traditional old concepts, Pavlov and his colleagues were unable to draw conclusions from objective facts, and easily lost the opportunity to discover a truth that was near them.

According to the traditional dominant doctrine of neurology at that time, which was also a particular belief of the Pavlovians, they believed that the pancreas secretion caused by hydrochloric acid was a reflection. They originally envisioned that both the vagus nerve and the large visceral nerve may be the efferent nerves of this reflex, because before that, they found that stimulating both groups of nerves could cause pancreas secretion. In 1896, another student of Pavlov, Popielski, analyzed the mechanism of the above phenomenon. He found that the response persisted after the bilateral vagus nerve, the bilateral splanchnic nerve, and the medulla oblongata were destroyed. He imagined that there might be a "peripheral reflex center" secreted by pancreatic juice in the pylorus of the stomach. From 1901 to 1902, the French scholar Wertherimer and others also performed the same mechanism analysis in France alone: he completely removed the free nerve of the small intestine loop of the experimental dog, leaving only the arteries and veins connected to other parts of the body. After injecting the hydrochloric acid solution into this small intestine, it can still cause pancreatic juice secretion. But he still believed that the response was "local secretory reflex", a stubborn local reflex. Because he believes that it is difficult to remove the nerves of the small bowel cleanly and thoroughly.

Secretin Bold Attempt

In January 1902, two British physiologists William M. Bayliss (1860 ~ 1924) and Starling (Ernest H. Starling (1866 ~ 1927)) were studying a local motion reflex in the small intestine and they saw A newly published paper by French scientist Wertheimer claims a stubborn local reflex between the small intestine and pancreas. They are very interested in this. They immediately repeated the above experiment by a French scholar with a dog, and confirmed his results. After placing the hydrochloric acid solution in this small intestine with the nerve removed, it indeed caused pancreatic juice secretion. But they are convinced that the nerve removal is complete. So how do you explain this result? They boldly jumped out of the traditional concept of "nerve reflex" and imagined that this might be a new phenomenon-"chemical reflex"; that is, under the action of hydrochloric acid, the small intestinal mucosa may produce a chemical substance when it is absorbed After entering the blood, the blood is transported to the pancreas, causing pancreatic juice secretion.

A new chapter on secretin

In order to confirm the above assumption, Starling immediately cut off another jejunum of the same dog, scraped off the mucous membrane, crushed with sand and dilute hydrochloric acid, neutralized and filtered the immersion solution to make a crude extract, and injected it into the same rod. The dog's veins were removed; as a result, pancreatic fluid secretion was more pronounced than in previous experiments of nerve removal. In this way, they fully confirmed their vision. A chemical substance that stimulates the secretion of pancreatic juice was discovered. This substance was named secretin. This is a great discovery in the history of physiology! They took the advice of their colleague WB Hardy and coined the word hormone in 1905, derived from the Greek word horman, which means incentive. Secretin is the first hormone discovered in history. In this way, a new concept of "hormonal regulation" and an "endocrine" way of transmitting hormones through the blood circulation were created, thereby establishing a new field of "endocrinology".