Which part of the small intestine is primarily responsible for the completion of digestion and nutrient absorption?

The primary site for the completion of digestion and nutrient absorption in the small intestine is indeed found in the jejunum and ileum.

The jejunum is the middle section of the small intestine, where most of the nutrient absorption occurs. Its structure, with numerous folds and villi, maximizes surface area for absorption, allowing for efficient uptake of carbohydrates, proteins, fats, vitamins, and minerals as chyme passes through.

Following the jejunum, the ileum continues the process of nutrient absorption, particularly for vitamin B12 and bile acids, which are critical for fat digestion. The ileum's specialized structures, such as Peyer's patches (associated with immune function), also play a significant role in the overall health of the intestinal environment.

Thus, while both the jejunum and ileum contribute significantly to digestion and absorption, stating that both are responsible acknowledges the roles they play in completing these essential processes in the small intestine.