Secretin

• Secretin is a hormone produced in the small intestine, primarily in response to acidic chyme entering the duodenum.
• Its main function is to stimulate the pancreas to release bicarbonate-rich fluid, neutralizing stomach acid and optimizing conditions for digestive enzymes.
• Secretin also inhibits gastric acid secretion and motility, further aiding in pH regulation.
• The role of secretin in body extends beyond digestion, influencing bile production and potentially other physiological processes.
• In medicine, secretin is utilized in diagnostic tests, such as the secretin stimulation test, to assess pancreatic function and diagnose certain conditions.

What is Secretin?

Secretin is a peptide hormone produced by S cells, which are enteroendocrine cells located in the mucosa of the duodenum, the first part of the small intestine. It is released into the bloodstream primarily when acidic chyme from the stomach enters the duodenum. This release mechanism makes secretin a key player in maintaining the delicate pH balance necessary for proper digestion.

As a vital gastrointestinal hormone, secretin is part of the secretin family of hormones, which also includes glucagon and vasoactive intestinal peptide (VIP). Its primary stimulus for secretion is a decrease in duodenal pH below 4.5, signaling the presence of highly acidic gastric contents. The role of secretin in body is fundamentally linked to protecting the small intestine from acid damage and creating an optimal environment for nutrient absorption.

Secretin’s Role in Digestion

The primary Secretin function in digestion is to regulate the pH of the duodenal contents. Upon its release, secretin travels through the bloodstream to its target organs, mainly the pancreas and the stomach. In the pancreas, it powerfully stimulates the secretion of a bicarbonate-rich fluid into the pancreatic duct. This bicarbonate acts as a buffer, neutralizing the acidic chyme and raising the pH in the duodenum to a level suitable for the activity of pancreatic digestive enzymes, which function optimally in a neutral to slightly alkaline environment.

Beyond its effects on the pancreas, secretin also influences gastric function. It inhibits gastric acid secretion and reduces gastric motility, slowing down the emptying of stomach contents into the duodenum. This coordinated action prevents an overwhelming influx of acid, allowing the bicarbonate from the pancreas to effectively neutralize the chyme. Furthermore, secretin stimulates the liver to produce bile, which aids in fat digestion and absorption.

Key digestive actions of secretin include:

• Stimulating pancreatic bicarbonate secretion to neutralize duodenal acid.
• Inhibiting gastric acid secretion and reducing stomach emptying.
• Promoting bile production by the liver.

Secretin Medical Applications

The unique physiological actions of secretin have led to its application in various medical diagnostic procedures. One of the most significant Secretin medical applications is the secretin stimulation test. This diagnostic test is used to evaluate pancreatic exocrine function, particularly in patients suspected of having chronic pancreatitis or pancreatic insufficiency. During the test, synthetic secretin is administered intravenously, and the pancreatic fluid collected is analyzed for bicarbonate concentration and volume. A diminished response can indicate pancreatic dysfunction.

Additionally, the secretin stimulation test is valuable in the diagnosis of gastrinomas, which are tumors that produce excessive amounts of the hormone gastrin, leading to Zollinger-Ellison syndrome. In healthy individuals, secretin inhibits gastrin release, but in patients with gastrinomas, secretin paradoxically stimulates gastrin secretion, making it a crucial diagnostic marker. While therapeutic applications of secretin are less common, its role in understanding and diagnosing gastrointestinal disorders remains significant in clinical practice.