Ileum – The ileum is the last and longest section of the small intestine. Here the walls of the small intestine begin to thin and narrow, and blood supply is reduced. Food spends the most time in the ileum, where the most water and nutrients are absorbed. It connects to the cecum (the first part of the large intestine). The ileum helps to further digest food coming from the stomach and other parts of the small intestine. It absorbs nutrients (vitamins, minerals, carbohydrates, fats, proteins) and water from food so they can be used by the body.

Duodenum – The first and shortest section of the small intestine and is a key organ in the digestive system. The small intestine’s most important function is to digest nutrients and pass them into the blood vessels—located in the intestinal wall—to absorb the nutrients into the bloodstream. To help break food down, the small intestine receives digestive juices from other organs in your digestive system, including your liver, gallbladder and pancreas. Ducts from these organs feed into the duodenum.

Appendix – It sits in the lower right abdomen. The function of the appendix is unknown. One theory is that the appendix acts as a storehouse for good bacteria, “rebooting” the digestive system after diarrheal illnesses.

References:
Christiansen, S. (2022). The Anatomy of the Duodenum. Retrieved from http://www.verywellhealth.com: https://www.verywellhealth.com/duodenum-anatomy-4780308
Clinic, C. (n.d.). Small Intestine. Retrieved from my.clevelandclinic.org: https://my.clevelandclinic.org/health/body/22135-small-intestine#:~:text=small%20intestine%20work%3F-,Duodenum,organs%20feed%20into%20the%20duodenum.
Sullivan, D. (2017). What Does the Appendix Do? Things to Know. Retrieved from http://www.healthline.com: https://www.healthline.com/health/what-does-the-appendix-do