Gastrin is produced by:
**Core Concept**
Gastrin is a peptide hormone produced in the gastrointestinal tract that plays a crucial role in regulating gastric acid secretion. The production of gastrin is primarily controlled by the hormone's interaction with specific receptors in the stomach lining.
**Why the Correct Answer is Right**
Gastrin is primarily produced by G cells, which are specialized endocrine cells located in the antrum of the stomach. When food enters the stomach, it stimulates the release of gastrin from G cells, which then binds to cholecystokinin type B (CCK-B) receptors on parietal cells, stimulating the secretion of gastric acid. This process is essential for breaking down food in the stomach.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because gastrin is not primarily produced by chief cells, which are responsible for secreting pepsinogen and other enzymes that help break down proteins in the stomach.
**Option B:** Incorrect because somatostatin, a hormone produced by D cells, actually inhibits gastrin release and gastric acid secretion, rather than producing gastrin.
**Option C:** Incorrect because enterochromaffin cells, also known as enterochromaffin-like cells (ECL cells), are involved in the production of histamine, which stimulates gastric acid secretion, but they are not the primary source of gastrin.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that gastrinomas, a type of neuroendocrine tumor, can lead to excessive gastrin production, resulting in Zollinger-Ellison syndrome, a condition characterized by severe peptic ulcers and gastric acid hypersecretion.
**Correct Answer: G cells. Gastrin is primarily produced by G cells.**