Final answer:
Parietal cells in the gastric glands secrete hydrochloric acid, critical for protein digestion and the activation of pepsin. They also produce intrinsic factor, necessary for vitamin B12 absorption. However, they do not secrete mucous, pepsin, or gastrin.
Step-by-step explanation:
The parietal cells of gastric glands primarily secrete hydrochloric acid (HCl). This substance is crucial for creating the acidic environment in the stomach, which is needed to activate the enzyme pepsin for protein digestion.
Hydrochloric acid is not only involved in digestion but also plays a role in combating ingested bacteria and denaturing proteins, thereby facilitating their breakdown by enzymes. The parietal cells also produce intrinsic factor, a glycoprotein essential for vitamin B12 absorption in the small intestine.
Different cells in the stomach contribute to its functioning. While chief cells secrete pepsinogen, which is activated by HCl into pepsin, enteroendocrine cells produce hormones like gastrin. However, it is the parietal cells that are responsible for the production of hydrochloric acid, not mucous, pepsin, or gastrin.