In protein digestion, which stage occurs first in the digestive process?

The initial stage of protein digestion takes place in the stomach, making gastric digestion the correct choice. During this stage, the enzyme pepsin is secreted in an inactive form known as pepsinogen. When pepsinogen comes into contact with the acidic environment of the stomach, it is activated to pepsin, which begins the breakdown of protein molecules into smaller peptides.

This process is critical because it prepares proteins for further digestion and absorption in the subsequent stages that occur in the pancreas, intestines, and colon. The gastric stage not only starts the mechanical breakdown of food but also sets the stage for further enzymatic action, as the smaller peptide chains need to be processed further by enzymes released from the pancreas in the next stage.

The other stages mentioned occur after the gastric stage. Pancreatic digestion follows, where additional enzymes continue the breakdown process in the small intestine. The intestinal stage refers to the absorption and further processing that happens in the small intestine. The colonic stage relates primarily to water absorption and fermentation of undigested food residues, occurring after protein digestion has largely been completed. Thus, the gastric stage is unequivocally the first in the series of steps involved in protein digestion.