The small intestine can be divided into three portions, viz. duodenum, jejunum and ileum.
Duodenum: This is the anterior- most portion of small intestine and is connected to pylorus. All the digestive juices come into duodenum and digestion of food takes place here.
Jejunum: This is the middle portion of small intestine. Absorption of most of the digested food takes place in jejunum. Absorption is carried by specialized cells which are called enterocytes.
Ileum: This is the last portion of small intestine and is connected to large intestine. Some of the substances which are not absorbed by jejunum are absorbed in this portion, e.g. bile salts and vitamins.