. Parietal cells secrete ________.
A. gastrin
B. hydrochloric acid
C. pepsin
D. pepsinogen
b) hydrochloric acid
- Correct: Parietal cells, also known as oxyntic cells, secrete hydrochloric acid (HCl) into the stomach lumen. HCl plays a critical role in the digestive process by creating an acidic environment necessary for the activation of pepsinogen to pepsin and for the breakdown of food proteins. Parietal cells also secrete intrinsic factor, which is essential for the absorption of vitamin B12 in the small intestine.
a) gastrin
- Incorrect: Gastrin is a hormone secreted by G cells in the gastric glands of the stomach. It stimulates the secretion of gastric acid (HCl) by parietal cells and promotes gastric motility and emptying.
c) pepsin
- Incorrect: Pepsin is an enzyme that digests proteins by breaking them down into smaller peptides. Pepsin is formed from the precursor molecule pepsinogen, which is secreted by chief cells in the gastric glands. Parietal cells do not directly secrete pepsin.
d) pepsinogen
- Incorrect: Pepsinogen is the inactive precursor of pepsin. It is secreted by chief cells in the gastric glands of the stomach. Pepsinogen is activated to pepsin by the acidic environment created by hydrochloric acid secreted by parietal cells.
Therefore, the Correct Answer is B.