The function of the relationship of the duodenum and ileum in the small intestine is to work together to digest the material passed from the stomach, making the nutrients available to be absorbed. A second part of the relationship between the duodenum and ileum is for the duodenum to receive and use pancreatic juices and bile to aid in digestion and for the ileum to reabsorb the byproducts of these secretions. This re-absorption allows for the recycling by the body of some of the components needed in digestion.
Located in the center of the abdomen, the small intestine is composed of the duodenum, located just after the stomach; the jejunum, the middle section of the small intestine; and the ileum, the last section of the small intestine. The duodenum, ileum, and jejunum are responsible for most of the breakdown and absorption of the food that passes from the stomach. These organs release to the body most of the nutrients and much of the energy available in the food that is eaten.
While the duodenum and ileum are both responsible the digestion and absorption of food, the relationship of the duodenum and ileum differs somewhat in the way each works. The first job of the duodenum is to counter the acidic nature of the chyme or the partially digested food passing from the stomach. In the duodenum, the acidic chyme is countered by the secretion of pancreatic juices, which contain high concentrations of bicarbonate ions, capable of neutralizing acid. Once the pancreatic juices are released, the environment inside the small intestine becomes much more hospitable. This makes it possible for enzymes, released by the duodenum and later the jejunum, to work to break down the protein and starch in the chyme.
The duodenum is responsible for the digestion and absorption of many nutrients. Calcium and iron, essential nutrients in many biological systems, are absorbed in the duodenum, as are the energy-bound molecules known as carbohydrate. In the duodenum, fat is emulsified by secreted bile into tiny globules called micelles, which allows the fat to be more readily taken up by the body.
The main role of the ileum is to complete the digestion and clean up the digestion juices used in the small intestine. To do this, the ileum will continue to break down the chyme and to absorb the final nutrients, especially vitamin B12. In addition, the ileum will soak up the remaining bile salts that were secreted by the duodenum and the jejunum and recycle the components to make new bile.