Jennifer's physician suspects she may have an ulcer in the _duodenum_, which is the first section of her small intestine.
The small intestine connects directly to the stomach via the pyloric sphincter. A peptic ulcer involves the spilling of very acidic stomach juice into the duodenum, which is the closest portion of the small intestine to the stomach. This can present as epigastric pain (in the upper center abdomen, just below the xiphoid process, or lower portion of the sternum). Usually it is brought on by ingesting acidic or spicy liquids, alcohol, or after going several hours without eating. Those ingestions can ramp up gastric acid production, and having nothing in the stomach allows pure acid to spill into the duodenum, which irritates an already eroded mucosal epithelium. Eating non-acidic, non-spicy foods like bread or milk helps to alleviate the pain by soaking up the acid in the stomach (bread) or neutralizing some of it (milk). But an empty stomach poses the largest risk of irritation. Also the epigastric region hones the pain in on the duodenum, since it crosses midline from the left upper abdomen (stomach) towards the right side as it continues on. If it were acutely painful in only the left upper quadrant (LUQ) of the abdomen, it would almost assuredly be gastritis or a gastric ulcer (gastro- meaning stomach).