**Core Concept:** Somatostatin is a peptide hormone produced by specific cells within the pancreas, playing a role in regulating various physiological processes, including insulin and glucagon secretion.

**Why the Correct Answer is Right:** Somatostatin is primarily produced by the D-cells in the islets of Langerhans within the pancreas. These cells are responsible for synthesizing and releasing somatostatin, which acts as a brake on insulin and glucagon secretion, helping to modulate blood glucose levels.

**Why Each Wrong Option is Incorrect:**

A. Alpha cells (alpha cells) are responsible for secreting glucagon, not somatostatin.
B. Beta cells (beta cells) produce insulin, not somatostatin.
C. Epsilon cells are not associated with somatostatin secretion; they secrete ghrelin, a hormone involved in appetite regulation and stomach motility.
D. Gamma cells are involved in producing and releasing ghrelin, not somatostatin.

**Clinical Pearl:** Understanding the role of somatostatin and its secretion helps in understanding glucose homeostasis, as well as recognizing the distinct functions of various pancreatic cell types.

**Correct Answer:** D. D-cells, also known as somatostatin-secreting cells, are the correct answer. They play a crucial role in regulating blood glucose levels and maintaining pancreatic homeostasis.