Final answer:
The middle portion of the small intestine is called the jejunum. It is responsible for absorbing most of the nutrients from digestion before passing the remaining contents to the ileum, the last part of the small intestine.
Step-by-step explanation:
The middle portion of the small intestine is known as the jejunum. The small intestine is divided into three main regions: the duodenum, the jejunum, and the ileum. The duodenum is the first part where most chemical digestion occurs. The jejunum is the second part, about 0.9 meters (3 feet) in length, connecting the duodenum to the ileum, and it plays a crucial role in the absorption of nutrients. The ileum is the final and longest part, associated with the absorption of bile salts and vitamins and it connects to the cecum of the large intestine. It is important to note that no clear demarcation exists between the jejunum and ileum. However, the jejunum is the specific segment where most of the absorption of the products of digestion, such as sugars, amino acids, and fatty acids, occurs.