Certified Neuroscience Registered Nurse (CNRN) Practice Exam

Which portion of the small intestine comprises the last three-fifths?

1. Duodenum

2. Jejunum

3. Ileum

4. Appendix

The correct answer is: Ileum

The correct response is the ileum, as it is the final and longest segment of the small intestine, accounting for approximately three-fifths of its total length. The small intestine is divided into three primary segments: the duodenum, jejunum, and ileum. The ileum plays a crucial role in nutrient absorption, particularly in absorbing vitamin B12 and bile salts, and it connects to the large intestine at the ileocecal valve. The structure of the ileum includes a greater abundance of lymphoid tissue known as Peyer's patches, which is important for immune function. In contrast, the duodenum, the first part of the small intestine, primarily functions in the initial phase of digestion and absorption, while the jejunum is involved in the absorption of nutrients but comprises only the middle portion. The appendix is not part of the small intestine; it is a small tube connected to the cecum of the large intestine, serving as a part of the gastrointestinal system but not involved in the digestion processes of the small intestine. This highlights the unique anatomical and functional roles each section plays within the digestive system.