The major physiological actions of secretin are stimulation of pancreatic fluid and bicarbonate secretion. S cells in the small intestine emit secretin. Gastric acid stimulates secretin release, allowing movement into the duodenal lumen.
Secretin, a digestive hormone secreted by the wall of the upper part of the small intestine (the duodenum) that regulates gastric acid secretion and pH levels in the duodenum. Secretin is a polypeptide made up of 27 amino acids.
Secretin release is inhibited by H2 antagonists, which reduce gastric acid secretion. As a result, if the pH in the duodenum increases above 4.5, secretin cannot be released.
Secretin causes the pancreas, liver, and stomach to release substances that help digest food. During a secretin stimulation test, a tube is inserted through the nose or throat into the stomach and small intestine. Secretin is given to the patient by injection into a vein.
| Endocrine gland/ source of hormone | Hormone | Target organ or tissue |
|---|
| Thyroid | Thyroxine (T4) Triiodothyronine (T3) | Most tissues |
| Calcitonin | Bone |
| Parathyroids | PTH (parathyroid hormone) | Bone, kidneys, intestine |
| Thymus (regresses in adulthood) | Thymopoetin | T-lymphocyte cells in blood |
CCK is produced by two separate cell types: endocrine cells of the small intestine and various neurons in the gastrointestinal tract and central nervous system.
The lower infusion rate produced increments in secretin in the blood within the range attainable during endogenous secretion. By comparison with effects of glucose alone each secretin infusion enhanced the increments of immunoreactive insulin in the blood.
Secretin is synthesized and secreted by S cells in the small intestine, and neurons in the brain. Secretin release is mainly stimulated by gastric acid delivered into the duodenal lumen. In addition, secretin is released by digested products of fat and protein.
What kinds of definition are used for “hormone” to replace “secretin”? “To excite” or “to set in motion” which translates to hormon in Greek were the definitions that are used for “hormone” to replace “secretin”.
Cholecystokinin (CCK) is well-known as a key hormone that inhibits stomach emptying and stimulates midgut motility in gastric species.
Pure secretin has shown to stimulate pepsin release in cats, dogs, and humans. Very small doses of secretin increase serum group pepsinogen I and pepsin output in young, healthy human volunteers.
Secretin stimulates the secretion of other substances. It helps digestion by causing the stomach to make pepsin, prompting the liver to make bile, and causing the pancreas to make digestive juices [3]. In addition, this hormone is important for processes that are involved in water/fluid balance [4].
Cholecystokinin is also known to stimulate secretion of bile salts into the biliary system.
The major nutrients that stimulate CCK release are fats and ingested proteins. Of these, the specific meal components that cause CCK release include fatty acids and amino acids. In some species, proteins appear to stimulate CCK secretion by virtue of their ability to inhibit intralumenal trypsin activity (20, 31).
The key difference between secretin and cholecystokinin is that the secretin is a peptide hormone produced by S cells of the duodenum and jejunum while the cholecystokinin is another peptide hormone secreted by I cells of the duodenum.
What is cholecystokinin? Cholecystokinin is produced by I-cells in the lining of the duodenum and is also released by some neurons in the brain. It acts on two types of receptors found throughout the gut and central nervous system. The most recognised functions of this hormone are in digestion and appetite.
Strategies to increase CCK:
- Protein: Eat plenty of protein at every meal ( 102 ).
- Healthy fat: Eating fat triggers the release of CCK ( 103 ).
- Fiber: In one study, when men ate a meal containing beans, their CCK levels rose twice as much as when they consumed a low-fiber meal ( 104 ).
Cholecystokinin is a potent inhibitor of gastric emptying. It is known to both relax the proximal stomach and contract the pyloric sphincter, and either one or both of these actions could mediate inhibition of gastric emptying.
Cholecystokinin, a hormone secreted by the APUD cells located in the proximal mucosa of the small intestine is administered intravenously, this stimulates the pancreatic secretion of the digestive enzymes amylase, trypsin, and lipase. These are measured by a catheter placed in the duodenum.
We conclude that endogenous CCK plays a significant role in fat-stimulated pancreatic secretion, and it is apparent that both endogenous CCK and secretin are equally important for stimulation of pancreatic bicarbonate secretion, which results from potentiation of the action of the two hormones.
CCK2 receptors have been localized to acid secreting cells in the the oxyntic mucosa of the stomach and extensively throughout the brain [19].
Also secretin exerts an inhibitory effect on gastric emptying. The peptide YY which is released from the ileum and colon after ingestion of carbohydrates or fat and which inhibits gastric acid secretion also reduces the amount of food emptied from the stomach.
What triggers the release of secretin from the small intestine? - The presence of acidic, fatty chyme in the small intestine causes the release of secretin. - This, in turn, inhibits further entry of stomach contents into the intestine until the fat has been emulsified and the pH raised.
The small intestine breaks down food from the stomach and absorbs much of the nutrients from the food. The duodenum is the first part of the small intestine. The main role of the duodenum is to complete the first phase of digestion.
Gastrin helps the pancreas produce enzymes for digestion and helps the liver produce bile. It also stimulates the intestines to help move food through the digestive tract. Sometimes a test for gastrin is done after eating a high-protein diet or after receiving an injection of the digestive hormone secretin into a vein.
