The initial relationship between the duodenum and jejunum is that they are both included as sections of the small intestine. Beyond the anatomical relationship, both sections of the small intestine work together to help digest food and absorb nutrients. In addition, the duodenum and jejunum share some of the same anatomical markers, such as folds and microvilli.
Part of the gastrointestinal system, the small intestine is a vital part of the digestive process. Located in the abdominal cavity, the small intestine extends from the pylorus, the emptying valve of the stomach, to the colic valve, which connects to the large intestine. Three segments, including the ileum, the jejunum, and the duodenum, make up the small intestine.
The shortest and widest part of the small intestine is the duodenum. This section is responsible for receiving food already processed by the stomach. In addition, digestive fluids and enzymes from both the pancreas and liver enter the duodenum through the sphincter of Oddi. The combination of the digestive juices and anatomical features of the duodenum, such as folds and small projections, assist in further digestion of stomach byproducts and allow for the absorption of nutrients.
As the small intestine continues, the relationship between the duodenum and jejunum becomes clear. The jejunum represents the part of the small intestine that connects the duodenum to the ileum. Specifically, the jejunum continues the nutrient absorption process by absorbing fats and other nutrients from the contents processed by the duodenum.
The digestion process of the duodenum and jejunum is similar, however, the consistency of the contents passing through varies. For instance, as food passes between the duodenum and the jejunum it takes on a more liquid consistency. The goal of the digestive process is to allow the small intestine to absorb all possible nutrients resulting in the remaining liquid being passed through the ileum into the large intestine for further processing.
Both sections of the small intestine, the duodenum and jejunum, have anatomical differences and similarities. The duodenum begins with a smooth lining and then changes to a lining featuring folds and small projections, referred to as villi and microvilli. These folds and projections continue along the jejunum to help continue the digestive process. Additional features of both sections of the small intestine include mucus to help lubricate the contents and blood vessels, which help transfer nutrients to the liver. This transport of nutrients to the liver is done through the hepatic portal vein.