Interaction of histamine with H2 receptor in parietal cell results in
**Core Concept**
The interaction between histamine and H2 receptors in parietal cells plays a crucial role in regulating gastric acid secretion. Histamine binds to H2 receptors on the surface of parietal cells, stimulating them to release gastric acid into the stomach lumen.
**Why the Correct Answer is Right**
When histamine binds to H2 receptors on parietal cells, it activates the enzyme adenylate cyclase, leading to an increase in cyclic AMP (cAMP) levels within the cell. Elevated cAMP levels stimulate the H+/K+ ATPase pump, also known as the proton pump, to secrete more hydrogen ions into the stomach lumen. This results in increased gastric acid production, which is essential for protein digestion and absorption.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because histamine's interaction with H2 receptors does not directly stimulate the release of gastrin, a hormone that also regulates gastric acid secretion.
* **Option B:** This option is incorrect because histamine's interaction with H2 receptors does not directly inhibit the release of gastric acid.
* **Option C:** This option is incorrect because histamine's interaction with H2 receptors does not directly stimulate the release of bicarbonate ions.
**Clinical Pearl / High-Yield Fact**
The H2 receptor antagonist class of drugs, including ranitidine and famotidine, works by competitively inhibiting histamine's binding to H2 receptors on parietal cells, thereby reducing gastric acid secretion.
**Correct Answer:** C. Stimulation of H+/K+ ATPase pump to secrete more hydrogen ions into the stomach lumen.