Which sequence of events correctly describes how hydrochloric acid and pepsinogen work together to digest proteins while minimizing damage to the gastric gland cells that produce them?

• A. HCl degrades pepsinogen into amino acids which are absorbed by parietal cells to prevent pepsin formation; pepsin forms later in the intestine where pH is neutral
• B. Parietal cells secrete HCl lowering pH and denaturing proteins; chief cells secrete inactive pepsinogen; low pH converts pepsinogen to active pepsin in the lumen where it cleaves denatured proteins, while protective mucus and local zymogen storage prevent autodigestion of gland cells
• C. Pepsinogen is secreted active and stored within parietal cells, HCl is only produced when food reaches the colon to prevent stomach damage
• D. Chief cells secrete pepsin which activates parietal cells to make HCl; HCl then synthesizes pepsinogen into an inactive storage form to protect gastric cells

Answer: (B)