HCI is secreted by which cells of stomach ?
**Core Concept**
The question is testing the student's knowledge of the gastric mucosa and the secretion of histamine, a key neurotransmitter involved in gastric acid secretion. Histamine plays a crucial role in the parietal cell's secretion of gastric acid, and its release is mediated by the vagus nerve and histamine-releasing cells in the stomach.
**Why the Correct Answer is Right**
Histamine is secreted by enterochromaffin-like (ECL) cells, which are a type of endocrine cell found in the gastric mucosa. When the vagus nerve stimulates the ECL cells, they release histamine, which binds to H2 receptors on the surface of parietal cells. This binding causes an increase in intracellular cAMP, leading to the secretion of gastric acid. The histamine also stimulates the release of gastrin, which further enhances gastric acid secretion.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ECL cells are not responsible for the secretion of gastrin, which is secreted by G cells.
**Option B:** This option is incorrect because chief cells are responsible for secreting pepsinogen, not histamine.
**Option C:** This option is incorrect because parietal cells are responsible for secreting gastric acid, not histamine.
**Clinical Pearl / High-Yield Fact**
ECL cells are also known as Leu cells because they contain the amino acid leucine. This is a classic histopathological finding in patients with pernicious anemia, where the ECL cells are increased in number.
**Correct Answer: D. ECL cells**