**Question:** D cells of pancreas secrete: September 2012

**Core Concept:**
The pancreas is an endocrine and exocrine gland located in the abdomen, responsible for producing hormones and enzymes essential for digestion and blood glucose regulation. D cells are a subpopulation of pancreatic endocrine cells that play a crucial role in blood glucose control.

**Why the Correct Answer is Right:**
D cells are known for their role in the production of glucagon, a peptide hormone that helps maintain blood glucose levels within a normal range. When blood glucose levels are too low (hypoglycemia), glucagon is released from D cells, stimulating the liver to convert glycogen into glucose through glycogenolysis and gluconeogenesis processes, thereby raising blood glucose levels.

**Why Each Wrong Option is Incorrect:**
A. Insulin (A) and somatostatin (B) are produced by other pancreatic cell types, specifically beta cells and D cells, respectively.
C. Glucagon is not secreted by pancreatic alpha cells (C), which primarily produce insulin and somatostatin.
D. Gastrin (D) is a hormone secreted by G cells of the stomach, not D cells of the pancreas.

**Why the correct answer is right and the wrong options are incorrect**:

D cells are responsible for glucagon production, which helps maintain blood glucose levels within a normal range by stimulating glycogen breakdown and gluconeogenesis when blood glucose levels are low.

**Core Concept**: Glucagon is a peptide hormone produced by D cells of the pancreas. It plays a vital role in regulating blood glucose levels by stimulating glycogenolysis and gluconeogenesis in the liver when blood glucose levels are low, such as during hypoglycemia.

**Why the Correct Answer is Right**: D cells are specifically responsible for glucagon production, ensuring proper glucose homeostasis in the body.

**Why the Wrong Options are Incorrect**:

A. Insulin (A) and somatostatin (B) are produced by other pancreatic cells, namely beta cells and D cells, respectively. These hormones have distinct roles in maintaining blood glucose levels and are not associated with the D cells.
C. Glucagon is produced by alpha cells (C), which are responsible for producing insulin, not glucagon. D cells are distinct from alpha cells and have different functions.
D. Gastrin (D) is produced by G cells of the stomach, not D cells of the pancreas. Gastrin and glucagon have different origins and functions within the gastrointestinal system.

**Why the correct answer is right and the wrong options are incorrect**:

D cells produce glucagon, ensuring proper glucose regulation in the body by stimulating glycogenolysis and gluconeogenesis in the liver during low blood glucose conditions, while insulin, somatostatin, and gastrin are produced by different pancreatic cells and have distinct functions within the gastrointestinal system.