Final answer:
Chief cells are the gastric cells that secrete pepsinogen, which is later converted to the enzyme pepsin in the presence of hydrochloric acid, produced by parietal cells in the stomach.
Step-by-step explanation:
The type of gastric cells that secrete pepsinogen, which is converted to the enzyme pepsin by hydrochloric acid during digestion, are the chief cells. These cells are located primarily in the basal regions of gastric glands. Once pepsinogen is secreted by the chief cells, it is in an inactive form.
The conversion to the active enzyme pepsin requires the presence of hydrochloric acid, which is secreted by a different type of cell known as the parietal cells. The parietal cells are located primarily in the middle region of the gastric glands, and they produce hydrochloric acid which creates a highly acidic environment in the stomach, essential for activating pepsin and facilitating the digestive processes.