Pancreas

The pancreas (plural: pancreata) is a retroperitoneal organ that has both endocrine and exocrine functions: it is involved in the production of hormones (insulin, glucagon and somatostatin), and also involved in digestion by its production and secretion of pancreatic juice.

Gross anatomy

The pancreas may have the shape of a dumbbell, tadpole or sausage. It can be divided into four main parts:

• head: thickest part; lies to the right of the superior mesenteric vessels (superior mesenteric artery (SMA), superior mesenteric vein (SMV))
  • uncinate process: extension of the head, posterior to SMV
  • attached to "C" loop of duodenum (D2 and D3)
• neck: thinnest part; lies anterior to SMA, SMV
  • SMV joins splenic vein behind pancreatic neck to form portal vein
• body: main part; lies to left of SMA, SMV
  • anterior surface is covered with peritoneum forming the posterior surface of the omental bursa (lesser sac)
  • splenic vein lies in groove on posterior surface of body
• tail: lies between layers of the splenorenal ligament in the splenic hilum

Pancreatic juice is secreted into a branching system of pancreatic ducts that extend throughout the gland. In the majority of individuals, the main pancreatic duct empties into the second part of duodenum at the ampulla of Vater. 

See article: Main pancreatic ducts for more information.duct

• runs length of pancreas draining tail, body, posteroinferior head and uncinate process
• joins the common bile duct at concavity of duodenum before entering D2 duodenum at major duodenal papilla

Accessory pancreatic duct

• drains anterosuperior part of head
• empties independently into D2 duodenum above and anterior to joint opening of chief pancreatic duct and common bile duct into minor duodenal papilla

Relations:

• posterior
  • L2 vertebral body
  • right kidney hilum, portal vein and IVC behind head 
  • common bile duct grooves posterior surface of upper part of head close to duodenum
  • aorta behind neck and uncinate process 
  • left kidney hilum, left suprarenal gland and right crus behind body 
  • splenic vein joined by inferior mesenteric vein, and confluence of splenic vein and superior mesenteric vein to form portal vein
• anterior
  • lesser sac separating it from stomach
  • lesser omentum and liver through it above the lesser curvature 
  • attachment of transverse mesocolon across head and lower margin of neck and body 
  • D1 duodenum anterior to (or above) head of pancreas 
  • infracolic compartment infrom of lower part of head, neck and body
• superior
  • origin of coeliac trunk
  • common hepatic artery runs to the right across upper margin of head and neck
  • splenic artery runs to the left across upper margin of body  

Blood supply

Arterial supply to the head is primarily from the inferior and superior pancreaticoduodenal arteries. Branches of the splenic artery supply the neck, body and tail via multiple branches including the dorsal pancreatic artery, greater pancreatic artery (arteria pancreatica magna) and transverse pancreatic artery.

The pancreaticVenous return is by numerous small veins into the splenic hilum. From the head the superior pancreaticoduodenal vein drains into the portal vein and the inferior pancreaticoduodenal veins drain bloodvein drains into the superior mesenteric vein. 

Innervation

• parasympathetic vagal fibres mainly from the pancreas draining to the splenic vein,posterior vagal trunk and coeliac plexus 
• sympathetic vasoconstrictor impulses via splanchnic nerves and the spleniccoeliac plexus (T6-T10)
• pain fibres accompany the sympathetic supply 

Lymphatic drainage

• left of the neck - retropancreatic node 
• upper head - coeliac group
• lower head and portal veins respectively. uncinate process - superior mesenteric group of pre-aortic nodes

Variant anatomy

Annular pancreas 

An annular pancreas is an uncommon (~1 in 20,000 ¹) variation with partial or complete surrounding of the duodenum with pancreatic tissue. The ventral pancreatic anlage is responsible for this anomaly by dividing early into two segments:

• often detected incidentally in asymptomatic patients
• may be associated with duodenal stenosis, postbulbar ulcerations, pancreatitis or biliary obstruction

Bifid pancreas

Rare branching anomaly of the pancreas tail and its duct system, also known as fishtail pancreas ⁶.

Ectopic pancreatic tissue

Ectopic pancreatic tissue refers to pancreatic rests that lie outside and separate to the pancreatic gland. It is reportedly quite common, affecting ~5% (range 1-10%) ¹ of people, most of whom are completely asymptomatic.

Recognised locations for ectopic pancreatic tissue include the gastric antrum, proximal duodenum, ileum and Meckel diverticula.

Pancreatic clefts

Linear clefts may be seen which contain fat where small vessels enter the pancreas and are a common mimic of pancreatic laceration. They are most prominent at the junction of the body and neck ².

Related pathology

• traumatic pancreatic injury
• pancreatitis
• pancreatic neoplasms
• pancreatic calcifications