Pancreas

Curved, ~15cm long.  Transv mesocolon attaches just above inferior border \ most of gland is in supracolic compartment. 

Development

2 buds, ventral & dorsal from respective mesogastria. 

Ventral lower head & uncinate process, dorsal rest. 

Head

Moulded to C of duodenal loop.  Overlies IVC and renal veins.  Uncinate process projects from L inferior margin behind SM vessels.
Is about 3-4cm thick; vs 1-2cm for body.

2 Ducts pass thro head: accessory duct (of Santorini) = minor papilla; main duct  (of Wirsung) = major papilla 2cm further distal. 
Main papilla usually 7cm distal to pylorus but may be at junction of D2 & D3, or in D3.
- minor papilla usually 2cm proximal and more anteriorly.

CBD and PD have common channel within duodenal wall to from ampulla of Vater in 70%; open separately into duodenum in 5%. 

- run in parallel for 2-10cm before uniting.
 
PD begins 2.5cm from tail (diam 0.5mm) body diam 1.5-3mm head diam 3.5mm. 

PD:  commonest arrangement = accessory duct communicating with both duodenum & main PD (40%).  Acc. duct may lose communication with duodenum (40%) or with PD. 

In remainder, accessory duct is main duct. 

Relations

Posteriorly: IVC, renal veins, CBD (latter may run within gland itself), posterior superior pancreaticoduodenal artery.
To L posteriorly lies portal vein & its formation by SMV and splenic vein. 

Anteriorly: hepatic flexure (which is acquiring a mesentery), anterior inferior pancreaticoduodenal artery, inferior pancreaticoduodenal vein.
- mobiliing pancreatic head off gland can cause tear to R colic veins communicating with the SMV at the head of the pancreas.

Vessels of head of pancreas & duodenum

Arterial supply mainly from coeliac axis; some SMA. 
Vessels approach duodenum from concavity of its C-shape \ mobilisation off IVC and aorta is bloodless. 

Supraduodenal artery

- when present, arises off the proximal GDA, passes above or behind bile duct.
Gastroduodenal artery

Gives off post superior p-d before terminal branching into anterior superior p-d and R gastroepiploic vessels.

Inferior Pancreaticoduodenal artery

From SMA --> anterior & post branches which anastomose with their superior counterparts, forming arcades supplying duodenum and pancreatic head.
--> avoid dissecting in plane between the pancreatic head and duodenum or may devascularize duodenum.

Variations

R Hepatic arises from SMA in 10% runs up behind head of pancreas.

High origin of middle colic artery, which may even emerge from pancreas itself at risk. 

Veins

Veins correspond to arteries but mode of emptying variable.  Inferior p-d veins most at risk operatively; may drain into side of SMV.  Middle colic vein drains into SMV where that passes behind neck of pancreas \ forms guide to SMV.   

Body & Tail

Neck overlies formation of portal vein (SMV + splenic). Body & tail incline up, back & to L.
Tail can be tucked into hilum of spleen, when at risk during ligations for splenectomy.
Stomach overlies this section, can be accessed by going through lesser omentum and elevating stomach posteriorly

Posteriorly: origin of SMA, splenic vein (which may be within pancreatic tissue).  Splenic vein can be located by tracing up IMV. 

Arterial Supply

Dorsal pancreatic artery from coeliac trunk or splenic artery R branch to head & uncinate process, L branch to rest. 
2-10 branches arise from splenic artery; one of these is larger (at middle-distal thirds) = arteria pancreatica magna ('great pancreatic artery' though smaller than dorsal artery). 

Venous Drainage

Numerous small veins drain into splenic which are vulnerable in dissection of splenic vein in pancreas-preserving splenectomy
Inferior pancreatic vein courses along bottom of gland; runs with the artery of same names.

Lymphatics

Tail --> splenic hilar nodes

Body & Head --> nodes corresponding to arterial supply.

- so Ca HOP can spread to nodes along the SMA.
Pain Fibres

Afferent pathways probaly run with sympathetic supply; interconnect through celiac and SM plexi
Often ablation of these pathways is unsuccessful, suggesting other patways active.


Other points


Annular Pancreas
Congential abnormality with a ring of pancreas around duodenum

Can compress it; duodenoduodenostomy warranted.