**Question:** Duodenum and Jejunum secrete ALL EXCEPT

A. Gastrin
B. Glucagon
C. Insulin
D. Somatostatin

**Core Concept:** The pancreas is an endocrine gland that plays a crucial role in maintaining glucose homeostasis by producing hormones that regulate blood glucose levels. The duodenum and jejunum are parts of the small intestine where the hormones secreted by the pancreas can exert their effects.

**Why the Correct Answer is Right:** Insulin and glucagon are the two primary hormones involved in blood glucose regulation. Insulin is released in response to high blood glucose levels, promoting glucose uptake into cells, while glucagon is released in response to low blood glucose levels, stimulating glycogenolysis and gluconeogenesis in the liver.

**Why Each Wrong Option is Incorrect:** Gastrin and somatostatin are also hormones secreted by the pancreas, but they are not primarily involved in glucose regulation. Gastrin stimulates the release of hydrochloric acid and pepsin from the stomach, while somatostatin inhibits the release of insulin, glucagon, and other gastrointestinal hormones. On the other hand, glucagon and gastrin are both involved in other physiological processes not directly related to glucose regulation.

**Duodenum and Jejunum Secrete:**

**Core Concept:** The duodenum and jejunum receive their blood supply from the superior mesenteric artery and vein. They are part of the small intestine, where nutrients are absorbed and processed after digestion in the stomach.

**Why Duodenum and Jejunum Secrete:**

**Core Concept:** The pancreas produces various hormones and enzymes that aid in digestion and nutrient absorption within the gastrointestinal tract. Duodenum and jejunum are the primary sites of action for these hormones and enzymes.

**Why Insulin and Glucagon are Not Secreted:**

**Core Concept:** Insulin and glucagon are primarily involved in glucose regulation, not digestion or nutrient absorption. In this context, they are not secreted by the duodenum and jejunum since their primary function is not related to digestion or nutrient absorption.

**Why Gastrin and Somatostatin are Secreted:**

**Core Concept:** Gastrin stimulates the secretion of hydrochloric acid and pepsin in the stomach, and somatostatin inhibits the release of insulin, glucagon, and other gastrointestinal hormones.

**Why Gastrin is Secreted:**

**Core Concept:** Gastrin is primarily secreted by the G cells located in the stomach's Gastric G cells. Gastrin stimulates the secretion of hydrochloric acid and pepsin from the gastric cells (chief cells) in the stomach, which aids in the digestion of proteins and neutralization of gastric juices.

**Why Somatostatin is Secreted:**

**Core Concept:** Somatostatin is secreted by the D cells in the stomach, pancreas, and duodenum. It acts as a brake on the digestive system by inhibiting