These fluids, which enter the duodenum through an opening called the sphincter of Oddi, are important in aiding digestion and absorption. Peristalsis also aids digestion and absorption by churning up food and mixing it with intestinal secretions. These villi and microvilli increase the surface area of the duodenal lining, allowing for greater absorption of nutrients. The rest of the small intestine, located below the duodenum, consists of the jejunum and the ileum. This part of the small intestine is largely responsible for the absorption of fats and other nutrients.
Absorption is enhanced by the vast surface area made up of folds, villi, and microvilli.
The intestinal wall is richly supplied with blood vessels that carry the absorbed nutrients to the liver through the portal vein. The intestinal wall releases mucus, which lubricates the intestinal contents, and water, which helps dissolve the digested fragments. Small amounts of enzymes that digest proteins, sugars, and fats are also released. The consistency of the intestinal contents changes gradually as they travel through the small intestine. In the duodenum, water is pumped rapidly into the contents to dilute the stomach acidity.