The duodenum begins to develop in the 4th week from the caudal-most part of the foregut and cranial part of the midgut. In the adult the junction of foregut and midgut lies just distal to the opening of the common bile duct. Thus, the first part of duodenum and second part upto the opening of the common bile duct develop from the foregut, whereas the rest of the second part and the third and fourth parts of the duodenum are derived from the midgut. Consequently, the duodenum receives its arterial supply from the branches of the celiac trunk (the artery of the foregut) and superior mesen-teric artery (the artery of the midgut).
The developing duodenum grows rapidly and forms a C-shaped loop that projects ventrally. The junc-,tion of the foregut and midgut is at the apex of this loop, just distal to the origin of the liver bud which grows out from
the ventral surface of duodenum. At this time the duodenum possesses a dorsal mesentery (mesoduodenum) that attache's the duodenum to the posterior abdomen wall.
Originally the C-shaped duodenal loop lies-in the sagittal plane. However, when the stomach rotates to the left, the duodenal loop rotates to the right and comes in contact with the posterior abdominal wall. Its mesentery is absorbed and, thus, the duodenum becomes retroperitoneal.
Initially the common bile duct opens into the duodenum at its ventral surface. Due to the rotation of the duodenal loop the ventral surface of duodenum becomes its right surface. Differential growth in the wall of the duodenum gradually shifts the opening of bile duct from the right surface to dor-somedial surface of the duodenum. When this shifting is complete, the common bile duct passes posterior to the second part of duodenum.
Like other portions of the gut tube, the lumen of the duodenum is also temporarily obliterated by the proliferation of the lining endodermal cells during the 5th and 6th week of development. However, normally, complete recanalization and restoration of the lumen occurs by the end of the 8th week.