Cells of gastric glands secrete two substances necessary for the active pepsin
The correct answer and explanation is:
Correct Answer:
The cells of the gastric glands secrete pepsinogen and hydrochloric acid (HCl), which are necessary for the active form of pepsin.
Explanation:
The gastric glands in the stomach lining contain different types of specialized cells that produce substances essential for digestion, particularly protein digestion.
- Pepsinogen secretion by Chief Cells:
Chief cells (also called zymogenic cells) in the gastric glands secrete pepsinogen, which is an inactive precursor (zymogen) of the enzyme pepsin. Pepsinogen itself is inactive to prevent the cells that produce it from being digested. - Hydrochloric acid secretion by Parietal Cells:
Parietal cells in the gastric glands secrete hydrochloric acid (HCl) into the stomach lumen. This acid has multiple critical roles:
- It creates an acidic environment in the stomach with a very low pH (around 1.5 to 3.5).
- The acidic pH is necessary to convert pepsinogen into its active form, pepsin. This conversion is an example of an activation by cleavage: HCl causes pepsinogen to unfold and cleave itself to form active pepsin.
- HCl also helps denature dietary proteins, making them easier targets for enzymatic digestion.
- It kills many microorganisms ingested with food, acting as a defense mechanism.
- Pepsin Function:
Once activated, pepsin is a protease enzyme that breaks down proteins into smaller peptides, aiding in their digestion and absorption later in the intestines.
Summary:
- Pepsinogen (from chief cells) + HCl (from parietal cells) → Active pepsin
- Pepsin breaks down proteins in the stomach under acidic conditions.
- This process is essential for the digestive system to efficiently process dietary proteins.
Understanding these cellular secretions helps explain how the stomach initiates protein digestion and protects itself from self-digestion by secreting enzymes in inactive forms until they reach the proper environment.