**Core Concept**
Peg cells, also known as intercalary cells or mucous neck cells, are a type of epithelial cell found in the stomach lining. They are characterized by their short, peg-like projections into the gastric lumen.

**Why the Correct Answer is Right**
Peg cells are involved in the secretion of mucus and are thought to play a role in protecting the stomach lining from acid damage. They are also involved in the production of pepsinogen, the inactive precursor to pepsin, a digestive enzyme. The presence of peg cells is an important diagnostic feature in the histopathological examination of gastric biopsies, particularly in the context of gastric ulcers and other gastric disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because peg cells are not a type of cell found in the small intestine.
**Option B:** This option is incorrect because goblet cells are a type of cell found in the intestinal tract, but they are not the same as peg cells.
**Option C:** This option is incorrect because parietal cells are a type of cell found in the stomach lining, but they are not the same as peg cells.

**Clinical Pearl / High-Yield Fact**
Peg cells are an important diagnostic feature in the histopathological examination of gastric biopsies, particularly in the context of gastric ulcers and other gastric disorders. They are also involved in the protection of the stomach lining from acid damage, making them an important consideration in the treatment of peptic ulcer disease.

**Correct Answer:** D.