Which of the following is NOT a segment of the small intestine?

The stomach is not a segment of the small intestine; instead, it is a distinct organ in the digestive system. The small intestine is comprised of three specific sections: the duodenum, jejunum, and ileum.

The duodenum is the first part of the small intestine and is where the majority of chemical digestion occurs, aided by bile and pancreatic juices. Following the duodenum is the jejunum, which is primarily responsible for nutrient absorption. The ileum, the final segment of the small intestine, continues the absorption process and is also involved in absorbing vitamin B12 and bile salts. Each of these segments plays a critical role in the digestive process, while the stomach serves a different function by breaking down food through mechanical and chemical means before it enters the small intestine.