Secretin is a hormone produced by the small intestine in response to acidic chyme entering from the stomach. Its primary role is to regulate the pH of the digestive tract by stimulating the pancreas to release bicarbonate. This bicarbonate neutralizes the acidity, creating a more suitable environment for digestive enzymes to function effectively. In addition to its effects on the pancreas, secretin also influences the liver to produce bile, which aids in fat digestion. Overall, secretin plays a crucial role in maintaining the balance of the digestive system, ensuring that food is processed efficiently and safely.