What do chief cells secrete in the stomach?

Chief cells, located in the gastric glands of the stomach, are responsible for the secretion of pepsinogen. This enzyme is a precursor to pepsin, which is crucial for protein digestion. When pepsinogen comes into contact with the acidic environment of the stomach, particularly hydrochloric acid secreted by parietal cells, it is activated to pepsin. This process is essential for breaking down proteins into smaller peptides, aiding in digestion.

While hydrochloric acid is secreted by parietal cells and mucous is produced by goblet cells and other cell types in the stomach lining, chief cells specifically focus on secreting pepsinogen. Thus, the other substances listed do not relate to the function of chief cells, confirming that pepsinogen is their primary secretion.