Embryonic origins of the relation of gastroesophageal reflux disease and airway disease.

The human tendency to have gastroesophageal reflux is a result of the upright stance, with the head and pelvis in the same plane, and bipedal locomotion. Compared with quadrupedal mammals, human embryologic developments shift in orientation, so that the ventral surface becomes anterior, the dorsal surface becomes posterior, anterior becomes dorsal, and posterior becomes ventral. Shifts in the position of the stomach and esophagus lead to relatively ineffective cardioesophageal sphincter mechanisms. This lends itself to reflux and reflux-associated problems. By the end of fetal development, all of the changes are present.