Neither the upper nor the lower portion of the esophagus has a well-defined sphincter muscle comparable to those located elsewhere along the digestive tract.

Question

Quizplus · Accepted Answer

The esophagus does not have a well-defined sphincter muscle like other parts of the digestive tract such as the pyloric sphincter and the anal sphincter. Rather, it has a functional sphincter mechanism created by the circular muscle fibers that constrict the esophagus at various points.

Neither the Upper nor the Lower Portion of the Esophagus