Pancreas

The pancreas (plural: pancreata) is an unpaired, mostly retroperitoneal organ that has endocrine and exocrine functions, involved in glucose metabolism and digestion.

Gross anatomy

Location

The pancreas is located at approximately the L1-L2 vertebral level in the anterior pararenal space of the retroperitoneum with the exception of its tail, which is intraperitoneal. It is an elongated, mostly midline structure which extends further left laterally. It lies slightly oblique with its tail more superior to its head. Developmentally, it is considered a secondarily retroperitoneal structure ⁶.

Structure

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, SMA ¹

  • lies within "C" shaped concavity 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 and is the only intraperitoneal part

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: pancreatic ducts for more information. 

Function

Its is involved in production of endocrine hormones, including insulin, glucagon, and somatostatin. Its exocrine function is secretion of enzymes involved with digestion.

Relations

• posterior

  • L1/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

  • 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 in front 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  

Arterial 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.

Venous drainage

Venous 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 vein drains into the superior mesenteric vein. 

lnnervation

• sympathetic: greater and lesser splanchnic nerves to the coeliac and superior mesenteric plexuses

• parasympathetic: from posterior vagal trunk

Lymphatic drainage

• follows blood vessels → collects in splenic, coeliac, superior mesenteric and hepatic nodes

Embryological development

The primitive pancreas develops from separate primordial buds in the dorsal and ventral mesogastrium, representing small evaginations from the foregut. The buds form around 32 days after ovulation and migrate to fuse into one gland at 41 days.

• dorsal pancreatic bud

  • develops into the anterior part of the head, body, and tail (and a small variable portion of the uncinate process)

  • contains a long duct continuing from the accessory pancreatic papilla to the tail

• ventral pancreatic bud​

  • smaller of the two buds that develops into the posterior part of the pancreatic head and most of the uncinate process

  • contains a short main pancreatic duct which is connected to the common bile duct

  • develops just distal to the developing biliary tree

  • starts to the right of the duodenum

  • rotates to the left underneath the dorsal pancreas

The ducts continue to fuse throughout the second and third trimesters but often continue into the neonatal period. Most of the dorsal duct drains into the proximal part of the ventral duct. The remaining proximal part of the dorsal duct forms the accessory duct.

Variant anatomy

• annular pancreas

• fishtail pancreas

• ectopic pancreatic tissue

• horseshoe pancreas

• accessory pancreas when head beneath mesenteric vessels separate

• pancreatic duct variations

• 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

• intrapancreatic accessory spleen

• Portal annular pancreas

• Agenesis or hypogenesis of the pancreas (rare)

Related pathology

• gamuts

  • hypervascular pancreatic lesions

  • cystic lesions of the pancreas

  • pancreatic calcifications

• neoplastic

  • pancreatic neoplasms

• traumatic

  • traumatic pancreatic injury

• Inflammatory

  • pancreatitis

• others

  • lipomatous pseudohypertrophy of the pancreas

  • pancreatic atrophy

  • pancreatic lipomatosis