Editing Small intestine (section)

== '''Duodenum''' ==
Structure

* C-shaped tube lying in front of the IVC and aorta. Loops around head of pancreas, which is at L2 level.
* Total length 25cm
* First 2.5cm are contained within the peritoneum of the lesser and greater omenta, but the rest is retroperitoneal
* Four parts:
** Superior (D1)
*** Proximal 2-4cm
*** Incorporating duodenal bulb
*** Lies in front of GDA, CBD, and PV
*** Lies posterior to GB/inferior surface of right lobe of liver
*** Pancreas inferomedially, but not intimately related
*** Separate blood supply to pancreas
** Descending (D2)
*** Commences at the superior duodenal angle, which is where the first circular fold is found
*** Retroperitoneal structure
*** Curves downwards over hilum of right kidney
*** HOP medially
*** Covered anteriorly with peritoneum, where the transverse mesocolon attachment crosses
*** Posteromedial wall receives common opening of CBD and main pancreatic duct
*** Contains valvulae conniventes/Kerckring's valves, which are the circular folds seen on endoscopy
*** Mobilisation
**** 'Kocher manoeuvre'
**** Incise the peritoneum along its right border
**** Elevate the duodenum anteriorly and to the left
**** Does not disrupt blood supply
** Horizontal (D3)
*** Curves forward from the right paravertebral gutter over the slope of the right psoas muscle, and passes over the forwardly projecting IVC and aorta to reach the left psoas muscle
*** Lies on commencement of IMA at inferior border
*** Posterior to base of small bowel mesentery containing SMA/SMV
*** Blood supply comes from pancreatic uncinate process
*** Hardest to mobilise because of the anterior relationships
** Ascending (D4)
*** Blood supply from branches off SMA
* Blood supply
** Superior and inferior pancreaticoduodenal arteries
** First 2cm receives blood from the hepatic, GDA, supraduodenal, right gastric and right gastroepiploic arteries
*** See 'liver' for full description of GDA/hepatic
** Venous drainage to tributaries of SMV and PV