What anatomic structure is represented by the letter D in an illustration of the stomach?

The pylorus is the correct answer because it is the anatomical structure that serves as the junction between the stomach and the small intestine. It plays a critical role in regulating the passage of partially digested food (chyme) from the stomach into the duodenum, the first part of the small intestine. The pylorus consists of the pyloric canal and pyloric sphincter, ensuring that food is adequately processed before moving on for further digestion and absorption.

When considering the other structures, the stomach encompasses the entire organ, and the duodenum and jejunum are sections of the small intestine, located distal to the stomach. The other options do not specifically describe the exit point of the stomach, which is what the pylorus represents. Recognizing the anatomical relationships and functions of these structures is crucial for understanding gastrointestinal physiology and the digestive process.