Pancreas: Parts, Relations, Ducts and Blood Supply

By Dr Richard Miller, MBChB FRCS · Reviewed 1 October 2026

The pancreas is a mixed exocrine and endocrine gland lying across the posterior abdominal wall at L1 to L2, behind the stomach. Its head sits in the C-loop of the duodenum and its tail reaches the splenic hilum. It is retroperitoneal except for the tail and draws blood from both the coeliac trunk and the superior mesenteric artery.

Pancreas · key facts

Location: Posterior abdominal wall, epigastrium to left hypochondrium, behind the stomach
Vertebral level: L1 to L2; the neck lies on the transpyloric plane (L1)
Blood supply: Superior pancreaticoduodenal (coeliac via gastroduodenal), inferior pancreaticoduodenal (SMA), splenic artery branches
Venous drainage: Splenic vein and superior mesenteric vein to the portal vein
Lymphatic drainage: Pancreaticosplenic, pyloric and pancreaticoduodenal nodes to coeliac and superior mesenteric nodes
Nerve supply: Vagus (parasympathetic) and thoracic splanchnic nerves via the coeliac and superior mesenteric plexuses
Function: Exocrine digestive enzymes and bicarbonate; endocrine insulin, glucagon and somatostatin

3D model of the pancreas: hepatic portal vein, pancreas, pancreatic duct and 5 more — 3D model showing the hepatic portal vein, pancreas, pancreatic duct and 5 more.BodyParts3D, © The Database Center for Life Science licensed under CC Attribution 4.0 International

Structure

The pancreas has five parts, named from right to left: head, uncinate process, neck, body and tail.

Head: the widest part, lying inside the concavity of the duodenum, to the right of the superior mesenteric vessels.
Uncinate process: a hook from the lower left of the head that passes behind the superior mesenteric vein and ends near the superior mesenteric artery.
Neck: a short constricted part in front of the portal vein, which forms behind it from the union of the superior mesenteric and splenic veins.
Body: crosses the aorta, the origin of the superior mesenteric artery, the left crus, left adrenal gland and left kidney.
Tail: the only intraperitoneal part, running in the splenorenal ligament with the splenic vessels to the hilum of the spleen.

Duct system

The main pancreatic duct runs the length of the gland, turns down in the head and joins the bile duct to form the hepatopancreatic ampulla (of Vater). This opens on the major duodenal papilla in the posteromedial wall of the second part of the duodenum, guarded by the sphincter of Oddi. An accessory pancreatic duct drains the upper head through the minor duodenal papilla, a short distance above the major papilla.

Development

The gland forms from dorsal and ventral buds. The ventral bud rotates behind the duodenum to form the lower head and uncinate process, and its duct becomes the proximal main duct. Failure of the ducts to fuse gives pancreas divisum; a ring of ventral tissue around the duodenum is an annular pancreas.

Relations

The pancreas lies behind the stomach, separated from it by the lesser sac, and in front of the great vessels, the left kidney and the bile duct.

Part	Anterior	Posterior
Head	Transverse colon and transverse mesocolon, jejunum	IVC, right renal vessels, left renal vein, bile duct in a groove or tunnel
Uncinate process	Superior mesenteric vein and artery	Aorta and IVC
Neck	Pylorus, gastroduodenal artery	Portal vein formation
Body	Stomach across the lesser sac	Aorta, SMA origin, left crus, left adrenal, left kidney, splenic vein
Tail	Splenic flexure of colon	Left kidney; ends at the splenic hilum

The splenic artery runs a tortuous course along the upper border of the body, while the splenic vein runs straight behind it. The transverse mesocolon attaches along the anterior border of the gland.

Blood supply and innervation

The head is supplied by an arcade formed by the superior and inferior pancreaticoduodenal arteries, and the body and tail by branches of the splenic artery.

The superior pancreaticoduodenal arteries (anterior and posterior) come from the gastroduodenal artery, a branch of the common hepatic artery from the coeliac trunk. The inferior pancreaticoduodenal artery comes from the superior mesenteric artery. Their anastomosis marks the junction of foregut and midgut territory. The splenic artery gives the dorsal pancreatic, great pancreatic and caudal pancreatic arteries to the body and tail.

Veins follow the arteries into the superior mesenteric and splenic veins, and so into the portal vein. Lymph drains to nodes along these vessels and finally to the coeliac and superior mesenteric nodes, which is why pancreatic cancer spreads early to nodes around both arteries.

Parasympathetic fibres from the vagus stimulate exocrine secretion. Sympathetic fibres from the thoracic splanchnic nerves reach the gland through the coeliac and superior mesenteric plexuses and carry its pain afferents, which explains epigastric pain radiating through to the back.

Clinical relevance

The deep central position of the pancreas means its disease often presents through the structures around it.

Carcinoma of the head: compresses the distal bile duct, causing painless obstructive jaundice with a palpable gallbladder (Courvoisier's law).
Acute pancreatitis: commonly follows a gallstone impacted at the ampulla, or alcohol. Fluid collects in the lesser sac and may mature into a pseudocyst.
Splenic vein thrombosis: from pancreatitis or tumour, gives left-sided portal hypertension with isolated gastric varices.
Pancreaticoduodenectomy (Whipple procedure): removes the head with the duodenum because they share the pancreaticoduodenal blood supply.
Blunt trauma: a seatbelt or handlebar can crush the neck or body against the L1 vertebra.
Splenectomy: the tail at the hilum can be injured, leading to a pancreatic fistula.

How it is examined

On a cadaveric spotter, in an OSPE and in MRCS Part B anatomy.

On a prosection of the posterior abdominal wall, the vessel emerging between the neck of the pancreas and the uncinate process is the superior mesenteric vein, with the artery on its left; the uncinate process lies behind the vein.
Examiners ask where the bile duct runs: behind the first part of the duodenum, then in a groove on the back of the pancreatic head, to join the main pancreatic duct at the ampulla.
Do not confuse the splenic artery (tortuous, on the upper border) with the splenic vein (straight, behind the body, receiving the inferior mesenteric vein in most people).
The standard viva follow-up is Courvoisier's law and why a head tumour gives jaundice while a tail tumour presents late.

Key points

The pancreas has a head, uncinate process, neck, body and tail, running from the duodenum to the spleen.
It is retroperitoneal except for the tail, which lies in the splenorenal ligament.
The portal vein forms behind the neck from the superior mesenteric and splenic veins.
The head is supplied by both the coeliac trunk and the SMA via the pancreaticoduodenal arcades.
The main pancreatic duct joins the bile duct at the ampulla, opening in the second part of the duodenum.

Common questions

Where is the pancreas located?

The pancreas lies across the back of the upper abdomen at the level of L1 to L2, behind the stomach and the lesser sac. The head sits in the C-shaped curve of the duodenum on the right, the neck lies in front of the portal vein, and the body and tail stretch to the left across the aorta and left kidney to the hilum of the spleen.

What arteries supply the pancreas?

The head and uncinate process are supplied by the superior pancreaticoduodenal arteries, from the gastroduodenal artery, and the inferior pancreaticoduodenal artery, from the superior mesenteric artery. These form anterior and posterior arcades. The body and tail are supplied by pancreatic branches of the splenic artery, including the dorsal pancreatic, great pancreatic and caudal pancreatic arteries. Venous blood drains to the portal vein.

Why does pancreatic cancer cause jaundice?

The distal bile duct runs through a groove or tunnel on the back of the pancreatic head before it joins the main pancreatic duct at the ampulla. A tumour in the head compresses the duct, blocking bile flow and producing obstructive jaundice with dark urine, pale stools and itching. The gallbladder often distends and becomes palpable, which is described by Courvoisier's law.

Is the pancreas retroperitoneal?

Most of the pancreas is secondarily retroperitoneal: the head, neck and body lost their mesentery during development and fused to the posterior abdominal wall, so they are covered by peritoneum only in front. The tail is the exception. It runs within the splenorenal ligament to the hilum of the spleen and is therefore intraperitoneal, which puts it at risk during splenectomy.

References

Gray's Anatomy: The Anatomical Basis of Clinical Practice. Standring S (ed). Elsevier. 42nd edition, 2020.
Moore's Clinically Oriented Anatomy. Moore KL, Dalley AF, Agur AMR. Wolters Kluwer. 9th edition, 2022.
Last's Anatomy: Regional and Applied. Elsevier.