In which part of the gut does motilin primarily exert its effects?

Motilin primarily exerts its effects in the upper small intestine. This hormone plays a key role in regulating gastrointestinal motility, particularly during the fasting state. It is secreted by the M cells in the duodenum, which is part of the upper small intestine, and acts on receptors in the gastrointestinal tract to stimulate the contraction of smooth muscle, enhancing peristalsis. This action effectively promotes the movement of food and waste through the digestive system.

Additionally, motilin is important for initiating the migrating motor complex, which helps to clear residual food and bacteria from the upper gastrointestinal tract during periods of fasting. This mechanism is crucial for maintaining gut health and preparing the digestive system for the next meal.