## **Core Concept**
Gastrin is a peptide hormone that stimulates the secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. Its release is a key component of the digestive process, promoting an acidic environment for protein denaturation and activation of digestive enzymes.

## **Why the Correct Answer is Right**
The correct answer, **G cells**, are a type of cell in the stomach lining, specifically found in the antrum and duodenum, responsible for the production and secretion of gastrin. When food enters the stomach, it stretches the gastric walls and increases the pH, triggering the release of gastrin from G cells. Gastrin then acts on parietal cells to increase the production of gastric acid.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Parietal cells are responsible for secreting gastric acid (HCl) in response to gastrin but do not produce gastrin themselves.
- **Option B:** Chief cells, or peptic cells, secrete pepsinogen, the inactive form of the digestive enzyme pepsin, but do not produce gastrin.
- **Option D:** Enterochromaffin-like cells (ECL cells) are involved in the regulation of gastric acid secretion, primarily through the release of histamine in response to gastrin, but they do not produce gastrin.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation is that gastrinomas, tumors that produce excessive amounts of gastrin, lead to Zollinger-Ellison syndrome. This syndrome is characterized by severe peptic ulcers, high levels of gastric acid secretion, and elevated gastrin levels.

## **Correct Answer:** C. G cells.