Which cells in the stomach secrete acid and which secrete mucus?

• A. Parietal cells secrete HCl; mucous cells secrete mucus; chief cells secrete pepsinogen
• B. Chief cells secrete mucus; mucous cells secrete HCl
• C. G cells secrete acid; parietal cells secrete mucus
• D. Enterocytes secrete mucus; enteroendocrine cells secrete acid

Answer: (A)

In the stomach, different secretory cells have distinct roles. Parietal cells produce hydrochloric acid (HCl), which creates the highly acidic environment needed for digestion and for activating enzymes. Mucous cells secrete mucus that coats and protects the stomach lining from that acid and from enzymes. Chief cells release pepsinogen, the inactive precursor of pepsin; once exposed to the acidic pH, pepsinogen is converted to pepsin to start protein digestion. So the acid is from parietal cells, mucus from mucous cells, and pepsinogen from chief cells. Some other cells, like G cells, regulate acid secretion with hormones, and enterocytes line the small intestine, not the stomach. This is why the pairing in the statement—acid with parietal cells and mucus with mucous cells—best fits the question.