Why does the esophagus have 2 layers of muscle fibers?

Related questions

1. What is the outer layer of the esophagus called?
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3. What causes esophagus to narrow?
4. What type of epithelium is in the esophagus?
5. What size is your esophagus?
6. Does the esophagus have villi?
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Tags

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2. #muscles
3. #known
4. #sphincter
5. #bottom
6. #peristalsis
7. #strong
8. #cardiac
9. #called
10. #through
11. #contractions
12. #layers
13. #includes
14. #fibres
15. #esophagus
16. #series
17. #esophageal
18. #muscle
19. #these
20. #lower
21. #there