S cell

S cells are a type of enteroendocrine cell found in the mucosa of the duodenum and, in smaller numbers, in the jejunum of the small intestine. They are responsible for the secretion of secretin, a hormone that plays a crucial role in the regulation of the body's bicarbonate levels. Secretin is particularly important in the digestive process, as it helps neutralize the acidic chyme entering the small intestine from the stomach, thereby protecting the intestinal lining and facilitating the action of digestive enzymes.

Function

The primary function of S cells is to produce and release secretin in response to the presence of acidic chyme in the small intestine. When the pH level in the duodenum drops, indicating the arrival of acidic chyme from the stomach, S cells are stimulated to release secretin into the bloodstream. Secretin, in turn, acts on the pancreas to secrete bicarbonate-rich pancreatic juice, which helps neutralize the acid. This mechanism is vital for the protection of the intestinal mucosa and the proper digestion and absorption of nutrients.

Secretin also has effects on the stomach, where it inhibits the production of gastric acid by the parietal cells, and on the liver and gallbladder, stimulating the production of bile, making it a key hormone in the digestive process.

Location and Structure

S cells are located in the mucosal layer of the duodenum and jejunum, embedded among other types of enteroendocrine cells. They are characterized by their ability to sense changes in the pH level of the intestinal contents. The exact mechanism by which S cells detect the acidity of chyme is still a subject of research, but it is known that they have receptors sensitive to hydrogen ions (H+), which allow them to respond to the acidity of the chyme.

Clinical Significance

Alterations in the function or number of S cells can lead to digestive disorders. For example, insufficient secretion of secretin can contribute to the development of duodenal ulcers by failing to neutralize stomach acid adequately. Conversely, excessive secretin production could lead to alkaline imbalances in the intestine.

Understanding the role and mechanisms of S cells and secretin has been crucial in the development of treatments for various gastrointestinal disorders, including therapies that mimic or inhibit the action of secretin.

Research Directions

Research on S cells continues to explore their broader role in gastrointestinal health and disease. Studies are investigating the potential of secretin and its analogs in treating conditions beyond traditional digestive disorders, such as autism spectrum disorders (ASD) and pancreatitis. The exploration of secretin's effects on the brain and nervous system opens new avenues for understanding and treating a range of conditions.