With all these normal daily activities that would trigger regurgitation, the esophagus seems to be highly exposed to reflux?
Actually the esophagus has many defenses against acid reflux and its consequences. Anatomical barriers in the form of muscles inside and outside(diaphragmatic) the wall of the esophagus enforce its lower sphincter to prevent reflux. Acid clearance from the lumen of the esophagus is mechanically assisted by gravity and its propulsive movement towards the stomach. Acid is chemically antagonized by saliva and the esophageal gland secretion.
The third mechanism against reflux is tissue resistance. It includes the bicarbonate content of the glandular secretions on the surface of the esophagus; the tight junctions between cells lining its lumen and the normal blood flow in the wall of the esophagus.
These defenses would be efficient only in cases of mild infrequent reflux.