Final answer:
A hiatal hernia involves the stomach protruding through the esophageal hiatus of the diaphragm, leading to potential digestive issues and discomfort.
Step-by-step explanation:
The anatomical structure involved in a hiatal hernia is C. Stomach. A hiatal hernia occurs when part of the stomach protrudes upward through the diaphragm, specifically through an opening called the esophageal hiatus, where the esophagus normally passes. Since the diaphragm separates the thoracic cavity from the abdominal cavity, this condition can lead to digestive issues as well as discomfort and requires proper medical attention.