**Question:** Motilin is secreted by cells in

A. Pancreas
B. Stomach
C. Small intestine
D. Enteric nervous system

**Correct Answer:** C. Small intestine

**Core Concept:** Motilin is a hormone that plays a significant role in the regulation of gastrointestinalmotility and gastric emptying. It is primarily involved in stimulating the release of gastric acid and promoting the contraction of the smooth muscle in the upper gastrointestinal tract.

**Why the Correct Answer is Right:** Motilin is secreted by enteroendocrine cells (G cells) in the small intestine. These cells are responsible for releasing various gastrointestinal hormones, including motilin, in response to the need for increased gastrointestinal motility and gastric emptying. When the stomach detects a decrease in pH or an increase in pressure, motilin is released, leading to the stimulation of the migrating motor complex (MMC), a cyclical series of contractions that help in the movement of food through the gastrointestinal tract.

**Why Each Wrong Option is Incorrect:**

A. Pancreas: Motilin is not secreted by the pancreas, which is responsible for producing digestive enzymes and hormones like insulin and glucagon.
B. Stomach: While motilin does stimulate gastric motility, it is not produced by the stomach itself but by the small intestine. The stomach is primarily involved in the secretion of gastric acid and the processing of food, not the regulation of gastrointestinal motility.
D. Enteric nervous system: While the enteric nervous system (ENS) is involved in the regulation of gastrointestinal motility, motilin is not a part of its regulation. The ENS plays a crucial role in controlling the smooth muscle contractions, but motilin is produced in the small intestine by enteroendocrine cells.

**Clinical Pearl:** The role of motilin in gastrointestinal motility regulation highlights the complex interplay between different gastrointestinal organs and the hormones they secrete. Understanding the physiological processes, such as the migrating motor complex (MMC), is essential for clinical practice, as it helps in assessing and treating gastrointestinal disorders related to impaired motility.