Which hormone is most associated with stimulating GI tract movement under normal circumstances?

The hormone most associated with stimulating gastrointestinal (GI) tract movement under normal circumstances is gastrin. Gastrin is produced by G cells in the stomach lining and plays a critical role in digestive physiology. Its primary function is to promote the secretion of gastric acid (HCl) from the parietal cells of the stomach, which aids in the digestion of food.

Additionally, gastrin also stimulates the motility of the stomach and enhances the contraction of the gastric muscles, facilitating the mixing and movement of food through the digestive system. This coordinated action helps ensure that food is broken down adequately and moves efficiently into the intestines for further digestion and nutrient absorption.

While pepsin is an enzyme that helps digest proteins in the acidic environment of the stomach, it does not actively stimulate GI tract movement. Insulin primarily regulates glucose levels in the blood and influences metabolism rather than directly affecting GI motility. Adrenaline (also known as epinephrine) typically has a suppressive effect on digestive processes during the 'fight or flight' response, as it diverts blood flow away from the digestive system to muscles and other critical areas. Therefore, gastrin is the hormone that most directly encourages appropriate movement within the gastrointestinal tract during regular digestive activities.