What are the three primary regions of the small intestine?

The three primary regions of the small intestine are the duodenum, jejunum, and ileum. This sequential organization reflects the functional and anatomical progression of the small intestine.

The duodenum is the first section of the small intestine, directly connected to the stomach. It plays a critical role in digestion, as it receives chyme from the stomach along with bile from the liver and pancreatic juices from the pancreas, which help to further break down food.

Following the duodenum is the jejunum, which is primarily responsible for the absorption of nutrients. It is characterized by a greater vascular supply and a higher surface area, thanks to its numerous folds and villi, which optimize nutrient absorption into the bloodstream.

Lastly, the ileum serves as the last section of the small intestine and continues the process of nutrient absorption, particularly vitamin B12 and bile salts. It also connects to the large intestine at the ileocecal valve.

This anatomical classification highlights the distinct roles each section plays in the digestive process, which aligns with the physiological functions characterized by their specialized structures.