**Core Concept**
Somatostatin is a regulatory peptide hormone involved in inhibiting the release of various hormones, including growth hormone, insulin, and gastrin. It plays a crucial role in the regulation of endocrine and exocrine functions in the body.

**Why the Correct Answer is Right**
Somatostatin is secreted by the delta cells of the pancreas, specifically in the islets of Langerhans. These delta cells produce and secrete somatostatin, which then acts on nearby cells to inhibit the release of other hormones. The somatostatin receptors, particularly SSTR2, are responsible for mediating the inhibitory effects of somatostatin. The action of somatostatin is mediated through G-protein coupled receptors, leading to a decrease in intracellular cAMP levels and subsequent inhibition of hormone release.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, but typically, other options might include incorrect sources of somatostatin secretion.
**Option B:** Other cells in the pancreas, such as alpha cells, secrete glucagon, not somatostatin.
**Option C:** The enteric nervous system is involved in regulating bowel movements and secretion, but it is not the primary source of somatostatin secretion.

**Clinical Pearl / High-Yield Fact**
Somatostatin analogs, such as octreotide, are used clinically to treat acromegaly, carcinoid syndrome, and other conditions characterized by excessive hormone production.

**Correct Answer:** D