The graph illustrates the activity level of three common digestive enzymes, across a range of pH values. Hydrochloric acid is us
ed by the stomach to aid in digestion and causes the stomach to have an average pH of 1.5 to 3.5. Which enzyme is likely to be active in the acidic environment of the stomach?
Digestion starts with the sight, thought, or smell of food. When the brain anticipates an incoming meal, the vagus nerve sends a message to the stomach causing the release of acetylcholine. The binding of acetylcholine to G cells in the stomach starts the secretion of gastrin and, in combination with acetylcholine and histamine, stimulates parietal cells in the gastric glands of the stomach body to start secreting hydrochloric acid (HCl).
