About Secretin

Secretin is a hormone that is synthesized and released into our body to aid the processes necessary for the body to function. Hormones are basically regulating substances that are vital for the body to function. The hormones can be natural, that is they are synthesized in our body or can be infused into the body via an external medium. When the hormone is produced in the body it is often by an organ and follows the path to its target. It is transported in tissue fluids like blood to stimulate specific cells or tissues into their respective action. There are many gastrointestinal hormones that are secreted by the organs engaging in carrying out the digestion process of the body. 

Role of Secretin Hormone in The Body

Secretin was discovered by William Bayliss and Ernest Starling in the year 1902 when they were researching the role of the nervous system in the digestion process and they determined that a substance secreted by the intestinal lining stimulates the pancreas and not the nervous system, after being transported via the bloodstream. They named this intestinal secretion “secretin” and it was the first hormone to be discovered however the term “hormone” was coined much later in the year 1905 by Starling. The secretin hormone was first identified and recognised as a ‘chemical messenger.’ Before diving into the secretin function and its effects on the body of the secretin hormone, let us understand the pathway of the digestive tract to understand the secretin hormone better.

Digestive System Pathway

The gastrointestinal tract has 12 parts that work together to process the food and in their order of function it starts from the mouth- where food is broken down into smaller digestible matter via chewing, this enters the oesophagus which is a long tube that transports food from the mouth to the stomach, the stomach releases several hormones and acids for further digestion post which it enters the small intestine which consists of three parts, the duodenum, jejunum and ileum and then enters the large intestine where waste products which do not aid in the betterment of the body reach the rectum followed by the anus.  Helping them along the way in the motility, digestion of food, absorption of food and secretion of hormones are the various other organs like the pancreas, gallbladder and liver.

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Secretin is produced by the small intestine of the digestive tract whose main function is maximum absorption of nutrients from the food consumed. When the food reaches the stomach hormone gastrin is released which creates an acidic environment for further digestion. After which the food reaches the small intestine and secretin hormone is secreted by the duodenum the S cells of the duodenum, which are located in the intestinal gland produce it. People often mistake these main hormones released by the gastrointestinal tract when in reality secretin and gastrin counteract each other’s function and maintain the equilibrium. Gastrin is a hormone that is secreted by the stomach-pyloric mucosa which stimulates the production of gastric acid in the stomach while secretin is a peptide hormone produced by the duodenum to regulate and balance the acidity created by the gastrin.

Release of The Secretin Hormone

The precursor of the secretin hormone is the prosecretin which is already during digestion. Secretin which is stored in the duodenum S cells in an inactive and unstable form is activated when prosecretin in the digested food enters the duodenum of the small intestine along with the gastric acid. The secretin release is thus triggered by the gastric acid for the purpose of protecting the duodenum from any sort of acid damage. When the duodenum increases above the pH of 4.5, the secretin release is blocked by the H2 antagonists and the basic pH is maintained once the secretion of the secretin hormone stops. 

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Structure of the Peptide Hormone Secretin

The Chemical Structure of the Secretin Hormone

The precursor prosecretin is a 120 amino acid protein that contains the secretin itself in the residues from 28-54, an N-terminal signal peptide, a 72- amino acid C-terminal peptide and a spacer. When this matures into the activated and stable secretin peptide, it becomes a linear peptide hormone. In the mature peptide hormone, a helix is formed between positions 5 and 13 of the amino acids. It has a molecular weight of 3055 and is composed of 27 amino acids. The mature peptide Secretin hormone also has valine which is an amidated carboxyl-terminal.  The sequence of amino acids is similar to glucagon where 14 of them reside in the same position as that of the mature peptide hormone secretin, and 10 of them reside in the same position as GIP (gastric inhibitory peptide) and 7 of the amino acids have the same place of residence as VIP (Vasoactive Intestinal Peptide). 

Function of Secretin 

  1. Secretin helps regulate the pH to a more neutral to basic state of the duodenum.

  2. Secretin inhibits the secretion of gastric acid when it is no longer required from the parietal cells of the stomach.

  3. Secretin functions by stimulating the production of various digestive chemicals and enzymes that help enhance the digestion and absorption process.

  4. The bicarbonate is stimulated by the secretin hormone from the ductal cells of the pancreas.

  5. Secretin also stimulates the liver for bile production that helps in emulsifying the dietary fats in the duodenum. 

  6. Alkalization of bile is also regulated by the secretin hormone.

  7. Secretion function by regulating the water homeostasis in the entire body.

  8. Secretin plays an important role in osmoregulation which is the active regulation of the osmotic pressure of an organism's body fluids by acting on the hypothalamus, pituitary gland, and kidneys.

  9. In concert with secretin's actions, simultaneously cholecystokinin (CCK), another hormone is issued by the duodenum, that stimulates the gallbladder contraction which enables the delivery of stored bile.

  10. Secretin hormone modulates water and transportation of electrolytes in epididymis epithelial cells, liver cholangiocytes and in pancreatic duct cells.

  11. It plays a vital role in the vasopressin-independent regulation in the kidneys for renal water reabsorption.

Secretin is an important hormone for the regulation of water and other fluids in the body and often its functional activity extends beyond just the small intestine. It activates the pancreatic enzymes which lend themselves to the absorption of the nutrients from the digested food. When the pancreas fails to respond to the activated secretin it is to be assumed that one suffers from cystic fibrosis, chronic pancreatitis, and pancreatic cancer. One can experience symptoms due to disentanglement or disengagement with the secretin hormone by the pancreas through signs of abdominal pain, nausea, and vomiting and initial stages of pancreatitis. 


This condition of pancreatic insufficiency is tested through a secretin stimulation test wherein a tube is inserted through the nose that passes through the oesophagus and stomach and extends till it reaches the duodenum. In the duodenum, the secretin hormone is injected intravenously and the response of the pancreas is then monitored and the damage or insufficiency is determined and the treatment is given accordingly. 


Ways to Balance Secretin Hormone Levels

  • To optimize hormone health,  a protein-rich diet is a must and experts recommend a minimum of 20–30 grams of protein consumption per meal. A Protein-rich food or meal must include meat, especially lean meats, seafood and poultry. 

  • Regular activity and engaging in some form of exercise be it dancing, yoga, strength training, aerobics, etc. will keep the hormonal balance game strong and one will be devoid of health problems.

  • Management of stress: When one is stressed, the release of hormones are affected and in most cases declination is seen that can be very concerning and lead to severe health problems.

  • Avoid refined foods and sugars that also damages the digestive system which messes up the secretin release as well.

  • Have healthy habits like consuming green tea, avoid undereating like do not starve yourself in the name of diets and other fads and there is no need for overeating as well, both are damaging in the long run.

  • Consume fatty fish and other healthy and good fats. Unlike the other diets that suggest avoiding fat, it is important to keep in mind that healthy fats are good for the body that aids hormone release. 

  • Having eggs and eating fibre-rich food is very crucial for hormonal balance. Fruits like berries, oranges, melon and pear, broccoli, carrots and sweetcorn are the high fibre containing vegetables and others are nuts and seeds.

  • Stay away from sugary and carbonated drinks that can damage your entire body and its functions.

  • The most important of all is to consistently get good sleep and not be sleep deprived to have a hormonally healthy and balanced body.

Conclusion

The digestive process is impossible without this important hormone secreted by the duodenum of the small intestine called secretin. The balance of it is important for physical and mental health as hormones like secretin also regulate water homeostasis. This chemical messenger also plays a major role in controlling the appetite as when there is no secretin, the acidity increases and slowly reaches other parts making it unlikely for the body to be able to consume more food. When secretin is produced in excess, it can also pose a problem. One must look at it that it is in an optimum release as per requirement and regular checkups and blood tests will help you keep a check on your health and when any issue is there, it can be diagnosed early and necessary changes can be made. 

FAQs (Frequently Asked Questions)

Q.1) Is the Secretin Hormone Secretion Triggered by Bodily Functions?

Ans.) The bodily functions are a great example of balancing and regulating all the functions necessary for the body to be active and do the work to maintain equilibrium. Secretin is one of the first hormones to be discovered which was initially referred to as a ‘chemical messenger’. The discovery was during a study on digestion and was determined that the release of this chemical messenger is stimulated by gastric acid. The gastric acid is released in the stomach and digests the food after which the food reaches the small intestine and the acidity due to the gastric acid triggers the secretion of the secretin hormone by the S cells in the upper part of the small intestine, that is the duodenum.  

Q.2) What Happens to the Body If There is No Release of Secretin Hormone?

Ans.) For the body to function properly and thrive in any environment, energy and balance are needed, and the secretion of the secretin hormone plays an important role in both of these processes. Osmoregulation and water homeostasis is regulated by the secretin and secretin is crucial for the release of pancreatic enzymes that absorb essential nutrients from the body which helps provide nutrition and energy to the body. The role of the secretin hormone is prominent even in the hypothalamus and kidneys and there are so many functions along with the aforementioned roles performed by the secretin hormone. Without it, the acidity will increase and curb the digestion process and then no other function can be carried out by the body. 

Q.3) Is Excess Production of Secretin Toxic to the Body?

Ans.) One of the main roles of secretin is to protect the duodenum from the acidity of the gastric acid released by the stomach cells. It helps neutralize the pH in the duodenum. Along with it, it also acts on the pancreas and the liver and gallbladder contraction to aid the release of pancreatic enzymes and bile juice respectively. And when the secretin release becomes more than required, the basic pH rises and the body does not function well in either highly acidic or basic functionality. The perfect balance of pH in our body is crucial for proper functioning.  Excess production of secretin is not a favourable condition for the body it can be damaging. 

Q.4) How is Gastrin Affected by Secretin?

Ans.) The gastrin hormone that creates an acidic environment for digestion is contradicted by the secretin hormone in order to protect other organs from acidity and helps neutralize the pH. Secretin affects gastrin by neutralizing its levels as it enters the duodenum which is the first part of the small intestine.