Which hormone is first released by the small intestine and helps to reduce the acidity of chyme?

The hormone released first by the small intestine that helps to reduce the acidity of chyme is secretin. Secretin plays a crucial role in the digestive process by signaling the pancreas to secrete bicarbonate into the small intestine. Bicarbonate neutralizes the hydrochloric acid present in chyme, the semi-liquid mixture of partially digested food and gastric juices that exit the stomach. This neutralization is essential for creating a suitable alkaline environment in the small intestine, allowing digestive enzymes to function optimally and facilitating proper nutrient absorption.

In addition to promoting bicarbonate release, secretin also regulates gastric acid secretion and slows down gastric emptying, ensuring that the digestive process in the small intestine is well-coordinated. The timing and release of secretin are crucial as they help maintain pH levels conducive to digestion and protect the intestinal lining from excessive acidity.