What causes the release of acetylcholine (ACh) in the duodenum?

The release of acetylcholine (ACh) in the duodenum is primarily stimulated by the presence of specific nutrients, such as fatty acids, amino acids, and hydrogen ions (H+). This release is part of the digestive process where ACh plays a crucial role in stimulating gastrointestinal motility and secretions.

When chyme enters the duodenum from the stomach, it is mixed with digestive juices and exposed to various stimuli. The presence of H+, fatty acids, and amino acids in the duodenum activates chemoreceptors in the intestinal lining. These receptors send signals to enteric neurons, which then lead to the release of ACh. The ACh facilitates contractions of the smooth muscle in the walls of the intestine, enhancing the digestive process and promoting further mixing of the chyme with digestive enzymes.

In contrast, while carbohydrates can promote various digestive processes, they do not directly trigger ACh release in the duodenum as effectively as the combination of H+, fatty acids, and amino acids. The response to high pH does not directly stimulate ACh release either; rather, a drop in pH due to the presence of acids is what more actively influences ACh release. The release of gastrin is important for promoting gastric