Which organ does NOT belong to the circulatory system?

The esophagus does not belong to the circulatory system; it is part of the digestive system. Its primary function is to transport food from the mouth to the stomach through a series of muscular contractions known as peristalsis. In contrast, the organs that are part of the circulatory system, such as the heart, veins, and arteries, are responsible for the movement of blood throughout the body, delivering oxygen and nutrients to tissues and removing waste products. The heart pumps blood, arteries carry oxygenated blood away from the heart, and veins return deoxygenated blood back to the heart. This fundamental difference in function clearly distinguishes the esophagus from the other organs listed.