Editing Duodenum (section)

===Parts===
The ''first'' or ''superior part'' of the duodenum is a continuation from the [[pylorus]] to the transpyloric plane. It is superior (above) to the rest of the segments, at the [[vertebral]] level of [[lumbar vertebrae|L1]]. The [[duodenal bulb]], about {{Convert|2|cm|in|abbr=on|frac=4}} long, is the first part of the duodenum and is slightly dilated. The duodenal bulb is a remnant of the mesoduodenum, a [[mesentery]] that suspends the organ from the posterior abdominal wall in fetal life.<ref>{{cite book|last=Singh|first=Inderbir|author2=GP Pal|title=Human Embryology|publisher=Macmillan Publishers India|location=Delhi|date=2012|edition=9|page=163|chapter=13|isbn=978-93-5059-122-2}}</ref> The first part of the duodenum is mobile, and connected to the liver by the [[hepatoduodenal ligament]] of the [[lesser omentum]]. The first part of the duodenum ends at the corner, the ''superior duodenal flexure''.<ref name="GRAYS2005">{{cite book|last=Drake|first=Richard L.|title=Gray's anatomy for students|year=2005|publisher=Elsevier/Churchill Livingstone|location=Philadelphia|isbn=978-0-8089-2306-0|author2=Vogl, Wayne |author3=Tibbitts, Adam W.M. Mitchell  |author4=illustrations by Richard |author5= Richardson, Paul }}</ref>{{rp|273}}

<!-- Only the first 2 cm of the superior part is mobile (covered by [[peritoneum]]) – the [[Anatomical terms of location#Proximal and distal|distal]] 3&nbsp;cm of the first part along with the rest of the duodenum is retroperitoneal (immobile). unsourced-->Relations:{{citation needed|date=December 2013}}
* Anterior
** [[Gallbladder]]
** [[Quadrate lobe of liver]]
* Posterior
** [[Bile duct]]
** [[Gastroduodenal artery]]
** [[Portal vein]]
** [[Inferior vena cava]]
** [[Head of pancreas]]
* Superior
** [[Neck of gallbladder]]
** [[Hepatoduodenal ligament]] ([[lesser omentum]])
* Inferior
** [[Neck of pancreas]]
** [[Greater omentum]]
** [[Head of pancreas]]
The ''second'' or ''descending part'' of the duodenum begins at the superior duodenal flexure. It goes [[Anatomical terms of location#Superior and inferior|inferior]] to the lower border of vertebral body L3, before making a sharp turn [[Lateral and medial|medial]]ly into the ''inferior duodenal flexure'', the end of the descending part.<ref name="GRAYS2005" />{{rp|274}}

The [[pancreatic duct]] and [[common bile duct]] enter the descending duodenum, through the [[major duodenal papilla]]. The second part of the duodenum also contains the minor duodenal papilla, the entrance for the [[accessory pancreatic duct]]. The junction between the embryological [[foregut]] and [[midgut]] lies just below the major duodenal papilla.<ref name="GRAYS2005" />{{rp|274}}

The ''third'', ''horizontal'' or ''inferior part'' of the duodenum is 10~12&nbsp;cm in length. It begins at the ''inferior duodenal flexure'' and passes transversely to the left, passing in front of the [[inferior vena cava]], [[abdominal aorta]] and the [[vertebral column]]. The [[superior mesenteric artery]] and [[superior mesenteric vein|vein]] are [[anterior]] to the third part of the duodenum.<ref name="GRAYS2005" />{{rp|274}} This part may be compressed between the aorta and SMA causing [[superior mesenteric artery syndrome]].

The ''fourth'' or ''ascending part'' of the duodenum passes upward, joining with the [[jejunum]] at the [[duodenojejunal flexure]]. The fourth part of the duodenum is at the vertebral level L3, and may pass directly on top, or slightly to the left, of the [[aorta]].<ref name="GRAYS2005" />{{rp|274}}