The small intestine is separated into three sections. Partially digested food from the stomach, or gastric chyme, enters the small intestine through the duodenum. Most of the nutrients are absorbed as it passes through the jejunum. Then, what remains of the chyme passes through the ileum to the large intestine.
As gastric chyme enters the duodenum, it mixes with bile from the liver, mucus rich bicarbonate secretions from the Brunner's glands, and pancreatic juice. The bicarbonate neutralizes the remaining stomach acid and the enzymes in the pancreatic juice break down proteins and bile and emulsify fats.
Sugars, amino acids, and fatty acids are absorbed into the bloodstream in the jejunum, as is about ninety five percent of the water and salt from the chyme. Afterward, the remaining solids move through the ileum, where vitamin B12, bile acids, and any other remaining nutrients are absorbed from the chyme before it passes into the large intestine.