Which three structures are visualized during an upper GI series?

During an upper GI series, the main structures that are visualized are the esophagus, stomach, and duodenum. This series primarily focuses on the upper portion of the gastrointestinal tract, which includes these specific areas. The esophagus is the tube that carries food from the mouth to the stomach, and the stomach is where food begins to be digested. The duodenum is the first part of the small intestine and follows the stomach, playing a crucial role in the digestion of food as it receives bile from the liver and digestive juices from the pancreas.

The other choices focus on structures that are not part of the upper GI series. For instance, the colon, rectum, and sigmoid are components of the lower gastrointestinal tract, while the gallbladder, liver, and pancreas, though involved in digestion, are not part of the upper GI tract series specifically visualized in this procedure. The upper GI series is designed to assess the function and structure of the esophagus, stomach, and the duodenum following the ingestion of a contrast medium, usually barium.