Final answer:
A hiatal hernia occurs when a portion of the stomach protrudes through the esophageal hiatus, an opening in the diaphragm that allows the esophagus to pass from the thoracic cavity to the abdomen.
Step-by-step explanation:
A hiatal hernia occurs when a portion of the stomach protrudes through the esophageal hiatus, which is an opening in the diaphragm. This muscular partition separates the thoracic cavity from the abdominal cavity and has openings to allow for structural passages between the two regions. Unlike the aortic hiatus, which is the opening in the diaphragm that allows passage of the thoracic aorta into the abdominal region to become the abdominal aorta, the esophageal hiatus is specifically associated with the part of the digestive system that sees the esophagus running through it to enter the abdomen. When a hiatal hernia occurs, the stomach pushes up through this opening, often resulting in various symptoms and potential complications.