Question

Which one of the following chemicals is responsible for the production of HCl in the stomach leading to irritation and pain ? 

• A. A
• B. B
• C. C
• D. D

Hint:

The connection between histamine and stomach acid is a classic example in medicinal chemistry. Remembering that histamine stimulates acid secretion helps in understanding the mechanism of action of a major class of antacid drugs, the H\(_2\) receptor antagonists (e.g., cimetidine, ranitidine).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks to identify the biological chemical that stimulates the secretion of hydrochloric acid (HCl) in the stomach. Excessive secretion of this acid causes hyperacidity, leading to symptoms like irritation and pain.
Step 2: Detailed Explanation:
The regulation of gastric acid secretion is a complex biological process. A key chemical messenger involved is histamine.
When food enters the stomach, histamine is released from certain cells in the stomach wall. It then binds to specific receptors (H\(_2\) receptors) on the surface of parietal cells. This binding triggers an internal signaling pathway within the parietal cells that activates the "proton pump" (H\(^+\)/K\(^+\)-ATPase), which actively secretes H\(^+\) ions into the stomach lumen. These ions combine with Cl\(^-\) ions to form HCl.
Overproduction or overstimulation by histamine can lead to excess acid, which is the cause of acidity and related problems. Drugs that are used to treat acidity, known as antacids, often work by blocking these histamine receptors (H\(_2\)-blockers like Ranitidine) or by neutralizing the acid directly.
Step 3: Identifying the Structure of Histamine:
We need to identify the correct chemical structure of histamine from the given options. Histamine is an amine derived from the amino acid histidine. Its chemical name is 2-(1H-imidazol-4-yl)ethanamine. It consists of an imidazole ring attached to an ethylamine chain (–CH\(_2\)CH\(_2\)NH\(_2\)).
- Option (A) shows a molecule with an imidazole ring and an ethylamine side chain. This is the correct structure of histamine.
- Option (B) is phenelzine, an antidepressant.
- Option (C) is serotonin, another neurotransmitter.
- Option (D) is saccharin, an artificial sweetener.
Step 4: Final Answer:
The chemical responsible for stimulating HCl production in the stomach is histamine, whose structure is shown in option (A).