The pancreas is a glandular organ located in the retroperitoneum between the duodenal curvature and the splenic hilum. It has both exocrine and endocrine functions and is anatomically classified into four parts: the head, neck, body, and tail. Because it is embryologically derived from the foregut, the pancreas receives arterial supply from the celiac trunk and its branches. The veins of the pancreas drain into the portal vein and the lymphatics eventually drain into the celiac, superior mesenteric, and splenic lymph nodes. The pancreas receives both sympathetic and parasympathetic innervation via the celiac ganglia. Histologically, the pancreas has two functional structures: the exocrine acinar glands and the endocrine pancreatic islets. The exocrine glands produce digestive enzymes, which are secreted into the duodenum, and the endocrine islets produce blood glucose-regulating hormones such as insulin and glucagon, which are secreted into the blood.
- Glandular organ
- Length: 12–15 cm
- Weight: approx. 80 g
- In the abdominal cavity, between the duodenal curvature and the splenic hilum
- Secondary retroperitoneal organ
- Caudal to the omental bursa
- At vertebral level L1/L2
- Endocrine: produces somatostatin, glucagon, insulin
- Produces digestive enzymes that aid the absorption of macronutrients
- Produces bicarbonate, which neutralizes chyme
Anatomical subdivisions of the pancreas 
- Neck: lies anterior to the portal vein
- Body: lies anterior to the aorta and extends to the left kidney
The uncinate process is posterior to the superior mesenteric vessels. The head, body, and tail of the pancreas lie anterior to the superior mesenteric vessels.
Pancreatic ducts 
Pancreatic duct (duct of Wirsung): extends from the tail to the head of the pancreas
- Joins with the common bile duct → together they form the (ampulla of Vater) → empties into the
- Hepatopancreatic sphincter (sphincter of Oddi): controls the secretion of bile and pancreatic fluid into the duodenum
- Accessory pancreatic duct (duct of Santorini): begins in the head and drains the pancreatic head and body → empties at the minor duodenal papilla
Tumors in the pancreatic head often cause bile duct obstruction and can manifest with painless jaundice.
Vasculature, lymphatics, and innervation of the pancreas 
- Head and neck: pancreatic veins → superior mesenteric vein → portal vein
- Body and tail: pancreatic veins → splenic vein → portal vein
- Lymphatics: celiac, superior mesenteric, and splenic lymph nodes → para-aortic lymph nodes
- > 90% of the pancreas
- Produces digestive enzymes that are secreted into the gastrointestinal tract (see below)
- Composed of serous glandular tissue that is separated into lobules by collagenous septae
- Units of secretory acinar cells surrounding a small lumen
- Secrete proenzymes (e.g., trypsinogen, chymotrypsinogen) into intercalated ducts → ducts eventually merge to form the pancreatic duct → duct carries the enzymes out of the pancreas and to the duodenum
- Centroacinar cells: pale cells in the center of the acini, which secrete bicarbonate ions into the pancreatic fluid
- Electron micrographs of acinar cells show:
Histologically, the exocrine pancreas closely resembles the salivary glands. However, unlike the salivary glands, the pancreatic exocrine glands lack myoepithelial cells in the acini and do not possess striated ducts. Additionally, centroacinar cells are unique to the pancreas.
- Produces different hormones that are primarily involved in the regulation of blood glucose levels (see below)
- Composed of islets of Langerhans embedded within the exocrine pancreas
Islet cell types
- Alpha cells are located peripherally and produce glucagon. and make up ∼20%
- Beta cells are located centrally and produce insulin. and make up ∼70−80%
- Delta cells are dispersed within the islets and produce somatostatin. and make up ∼5%
- Epsilon cells are dispersed and make up ∼1%.
- Pancreatic polypeptide cells (formerly gamma cells) are dispersed throughout and make up ∼1%.
Pancreatic ducts 
- Smaller ducts have cuboidal epithelium; larger interlobular ducts have columnar epithelium.
- Most pancreatic malignancies are adenocarcinomas that originate in the ductal epithelium. 
The majority of pancreatic malignancies are located in the head of the pancreas and originate from epithelial cells within the tubules.
Content of secretions
- Digestive enzymes
Trypsin and chymotrypsin: digestion of proteins (proteases)
- Secreted as proenzymes (e.g., trypsinogen, chymotrypsinogen) by the pancreatic acinar cells into the pancreatic duct
- Activated in the duodenum: Trypsinogen is activated by enterokinases on the surface of the duodenal mucosa to form trypsin; once activated, trypsin activates chymotrypsinogen to form chymotrypsin.
- Pancreatic amylase: digestion of carbohydrates
- Pancreatic lipase: digestion of lipids
- Phospholipase A: digestion of phospholipids
- Nucleases: digestion of RNA/DNA
- Elastase: digestion of elastin fibers
- Trypsin and chymotrypsin: digestion of proteins (proteases)
- Electrolytes (Na+, K+, Cl-)
Cystic fibrosis is caused by a defective chloride channel that impairs pancreatic water and electrolyte secretion. This results in obstruction of the pancreatic ducts, with subsequent maldigestion and malabsorption.
- Inhibition: somatostatin
Acute pancreatitis leads to activation of the pancreatic enzymes within the pancreatic ducts, which also leads to subsequent autodigestion of pancreatic tissue.
Main endocrine cell types and hormones produced 
|Cell types||Substance secreted||Function||Feedback mechanism|
|ε-cells|| || |
|PP cells (formerly γ-cells)|| || || |
Insulin synthesis and secretion 
- Insulin gene transcription and translation in the rER of pancreatic β-cells → preproinsulin (precursor protein)
- Signal proteases remove the signal peptide of preproinsulin → proinsulin
- Protein folding and formation of one disulfide bridge in the α-chain and two disulfide bridges between the α-chain and β-chain
- Proinsulin is transported to the Golgi apparatus → packaged in membrane-bound secretory granules with proprotein convertases
- Proinsulin is cleaved by proteases → mature insulin + C-peptide
- Secretion of insulin and C-peptide via exocytosis
C-peptide is released by the β-cells in an equimolar proportion to insulin but is not present in exogenous insulin. It can, therefore, be used to differentiate between endogenous (e.g., insulinoma) and exogenous hyperinsulinism.
- Origin: derived from the foregut (endoderm)
The endoderm forms ventral and dorsal pancreatic buds.
- Ventral pancreatic bud → main pancreatic duct, uncinate process, lower part of pancreatic head
- Dorsal pancreatic bud → rest of pancreatic head, neck, body, and tail
- Foregut rotation → ventral pancreatic bud fuses with the dorsal pancreatic bud
- Secondary retroperitonealization
- The pancreas comes to rest under the lesser sac (omental bursa).
- The endoderm forms ventral and dorsal pancreatic buds.
Impaired development 
- Annular pancreas: a ring surrounding the duodenum is formed because of fusion and incomplete rotation of the pancreatic buds during foregut rotation → causes constriction of the duodenum
- Pancreas divisum
- See also .