Small intestine : Small intestine is distinguishable into three regions, a ‘C’ shaped duodenum, a long coiled middle portion jejunum and a highly coiled ileum.

(1) Duodenum : It has a length of 25 cm. It is C-shaped. The accessory pancreatic duct and haptopancreatic duct opens into duodenum independently. The haptopancreatic duct brings bile and pancreatic juice from gall bladder and pancreas into duodenum respectively. Its opening is guarded by sphincter of oddi. In duodenum, mainly digestion of food occurs. The bile and pancreatic juice act on food in duodenum.

(2) Jejunum : It has a length of bout 6.0 – 7.00 m. Jejunum has length of 4 m and ileum has length of 2.5 m.

(3) Ileum : It is 3 cm wide and is highly coiled. In jejunum-ileum digestion is completed. The inner lining of jejunum-ileum has folds called villi. The cells of villi has microvilli which increase the absorptive surface area.