Small intestine – It helps to further digest food coming from the stomach. It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.

Appendix – is designed to protect good bacteria in the gut. That way, when the gut is affected by a bout of diarrhea or other illness that cleans out the intestines, the good bacteria in the appendix can repopulate the digestive system and keep you healthy.

Esophagus – The esophagus functions to transport masticated and swallowed material (a bolus) through the mediastinum from the pharynx to the stomach.

References:
Hirsch, A. (2020). The Importance of Digestive Health. Retrieved from http://www.austingastro.com: https://www.austingastro.com/2020/02/07/the-importance-of-digestive-health/
M.Treuting, P. (2012). Upper Gastrointestinal Tract. Retrieved from http://www.sciencedirect.com: https://www.sciencedirect.com/science/article/pii/B9780123813619000111
Warner, J. (2007). Appendix May Actually Have a Purpose. Retrieved from http://www.webmd.com: https://www.webmd.com/digestive-disorders/news/20071012/appendix-may-have-purpose#:~:text=Researchers%20deduce%20that%20the%20appendix,system%20and%20keep%20you%20healthy.