There are species variability of esophageal muscle.

• A. True
• B. False
• C. Not specified
• D. Partially

Answer: (A)

There is species variability in esophageal muscle, which makes the statement true. Across different species, the proportion and arrangement of skeletal (striated) versus smooth muscle in the esophagus differ, and even where the transitions occur can vary. In humans, for example, the upper part is largely skeletal muscle under voluntary control, with a gradual shift to smooth muscle toward the lower end, reflecting both voluntary and reflexive control of swallowing. Other animals can have more smooth muscle throughout the esophagus or different regional patterns altogether. This variation across species is well documented, so the claim that there is species variability is accurate.