Final answer:
An upper GI series (barium swallow) is used to examine the upper gastrointestinal (GI) tract, which includes the mouth, pharynx, esophagus, and stomach.
Step-by-step explanation:
An upper GI series (barium swallow) is used to examine the upper gastrointestinal (GI) tract. This includes the mouth, pharynx, esophagus, and stomach. During the procedure, the patient swallows a contrast agent called barium, which coats the gastrointestinal tract and provides greater detail in the X-ray images taken.