Pancreas: Location, Anatomy, and Dual Endocrine-Exocrine Functions

The pancreas is a retroperitoneal gland located in the upper left abdomen (epigastrium and left hypochondrium), posterior to the stomach, spanning the transpyloric plane (L1–L2). It measures ~15–20 cm long, ~2.5–3 cm thick, and weighs 70–100 g.

Anatomic Relations

• Head: Nestled in C-loop of duodenum (right side)
• Neck: Overlies portal vein formation (SMV + splenic vein)
• Body: Crosses aorta, IVC, left renal vein, superior mesenteric artery
• Tail: Extends to splenic hilum (left side)
• Ducts: Main pancreatic duct (Wirsung) joins common bile duct → ampulla of Vater → duodenum. Accessory duct (Santorini) may drain separately.

Exocrine Function (99% of mass) — Digestion

Acinar cells secrete digestive enzymes into the ductal system → duodenum:

• Proteases: Trypsinogen, chymotrypsinogen, procarboxypeptidases (activated in duodenum)
• Lipases: Pancreatic lipase (triglycerides), phospholipase A2, cholesterol esterase
• Amylase: Carbohydrate digestion (starch → maltose)
• Nucleases: DNA/RNA digestion
• Bicarbonate-rich fluid: Ductal cells neutralize acidic chyme (pH 7–8 optimal for enzymes)

Regulation: CCK (enzymes), secretin (bicarbonate), vagal stimulation.

Endocrine Function (1–2% of mass) — Glucose Homeostasis

Islets of Langerhans (1–2 million clusters):

• β-cells (60–70%): Insulin — lowers blood glucose (promotes uptake, storage, synthesis)
• α-cells (20–25%): Glucagon — raises blood glucose (glycogenolysis, gluconeogenesis)
• δ-cells (~5%): Somatostatin — inhibits insulin/glucagon/growth hormone
• PP-cells (~1%): Pancreatic polypeptide — regulates exocrine secretion, appetite
• ε-cells (rare): Ghrelin — hunger signaling

Clinical Relevance

• Acute pancreatitis: Premature enzyme activation → autodigestion (gallstones, alcohol top causes)
• Diabetes mellitus: Type 1 (β-cell destruction), Type 2 (insulin resistance + β-cell failure)
• Pancreatic cancer: Adenocarcinoma (90%); often late presentation; poor prognosis
• Exocrine insufficiency: Cystic fibrosis, chronic pancreatitis → malabsorption