Pancreatic Anatomy and Physiology

Pancreatic Anatomy and Physiology

Pancreatic Anatomy and Physiology

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Gross Anatomy - Pancreas Unveiled: Prime Position

  • Location: Primarily retroperitoneal (except tail); epigastrium & left hypochondrium (L1-L2 vertebrae).
  • Parts & Relations:
    • Head: Cradled by C-loop of duodenum. Uncinate process hooks posterior to Superior Mesenteric Vein (SMV) & Artery (SMA).
    • Neck: Overlies SMV, portal vein formation.
    • Body: Crosses aorta, L2 vertebra; posterior to stomach.
    • Tail: Reaches splenic hilum; only intraperitoneal part. 📌 Mnemonic: "Tail In Peritoneum" (TIP).
  • Arterial Supply:
    • Head/Uncinate: Superior (from Gastroduodenal Artery) & Inferior (from SMA) pancreaticoduodenal arteries.
    • Body/Tail: Splenic artery branches.
  • Venous Drainage: Parallels arteries; drains to portal system (SMV, splenic vein).

Pancreas anatomy with surrounding organs and ducts

⭐ The uncinate process of the pancreas passing posterior to the superior mesenteric vessels (SMV and SMA) is a critical surgical landmark and a common site for tumor involvement affecting resectability.

Vascular & Ductal System - Red Rivers & Duct Tales

Arterial Supply:

  • Pancreaticoduodenal Arcades: Key anastomotic loops.
    • Superior Pancreaticoduodenal A. (SPDA): from Gastroduodenal A. (GDA ← Celiac Trunk)
    • Inferior Pancreaticoduodenal A. (IPDA): from Superior Mesenteric A. (SMA)
  • Splenic Artery Branches: (Supply body/tail)
    • Dorsal Pancreatic A.
    • Great Pancreatic A. (Arteria Pancreatica Magna)
    • Caudal Pancreatic A.

Venous Drainage: (Generally mirrors arterial supply)

  • Pancreaticoduodenal Veins → drain into Superior Mesenteric Vein (SMV) / Portal Vein (PV)
  • Splenic Vein + SMV = Portal Vein (forms posterior to pancreatic neck)

Ductal System:

  • Main Pancreatic Duct (Wirsung):
    • Runs tail → head; joins Common Bile Duct (CBD) → forms Ampulla of Vater.
    • Opens at Major Duodenal Papilla (2nd part of duodenum).
    • Diameter: Head ~3mm, Body ~2mm, Tail ~1mm (📌 3-2-1 Rule).
  • Accessory Pancreatic Duct (Santorini):
    • Drains superior/anterior part of head; opens at Minor Duodenal Papilla.
  • Pancreas Divisum: Commonest congenital anomaly; failure of ventral & dorsal duct fusion.

Pancreatic vascular and ductal anatomy

⭐ The Portal Vein is formed by the confluence of the Splenic Vein and Superior Mesenteric Vein (SMV) posterior to the neck of the pancreas, a critical surgical landmark during pancreatectomy.

Histo & Exocrine Role - Cell City & Enzyme Elixir

  • Histology - The "Cell City":
    • Acinar cells: Pyramidal, house zymogen granules (inactive enzyme precursors).
    • Centroacinar cells: Pale cells at duct origin within acinus; secrete bicarbonate.
    • Ductal cells: Cuboidal; secrete large volumes of bicarbonate-rich fluid.
  • Exocrine Function - The "Enzyme Elixir":
    • Daily secretion: 1.5-3 L of alkaline pancreatic juice (pH ~8).
    • Key Enzymes:
      • Proteolytic: Trypsinogen, Chymotrypsinogen.
      • Lipolytic: Lipase, Colipase.
      • Amylolytic: Amylase.
    • Bicarbonate ($HCO_3^-$): Neutralizes acidic chyme from stomach.
    • Primary Stimulators:
      • Cholecystokinin (CCK): ↑ Enzyme release from acini.
      • Secretin: ↑ $HCO_3^-$ and water secretion from ducts.

Pancreatic histology: acini, ducts, and islets

⭐ Trypsinogen is activated to trypsin by duodenal enterokinase (enteropeptidase). Trypsin then auto-catalyzes more trypsinogen and activates other zymogens (e.g., chymotrypsinogen to chymotrypsin), a critical step preventing pancreatic auto-digestion.

Endocrine Role & Embryology - Sugar Bosses & Budding Beginnings

  • Islets of Langerhans (Endocrine Pancreas): Scattered cell clusters.
    • β-cells (60-70%): Insulin (↓ blood glucose), Amylin.
    • α-cells (20-25%): Glucagon (↑ blood glucose).
    • δ-cells (5-10%): Somatostatin (inhibits insulin, glucagon, GH).
    • PP/γ-cells (1-2%): Pancreatic Polypeptide (inhibits exocrine secretion, gallbladder contraction).
    • 📌 Mnemonic: Inside Beta, Glucagon Around (Insulin by Beta cells in center, Glucagon by Alpha cells in periphery).
  • Embryology: Dual origin from foregut endoderm.
    • Dorsal bud → Superior head, body, tail.
    • Ventral bud → Inferior head, uncinate process.
    • Rotation & fusion by 5th-7th week gestation.
    • Duct of Wirsung (main): Ventral duct + distal dorsal duct.
    • Duct of Santorini (accessory): Proximal dorsal duct.

⭐ Annular pancreas, a congenital anomaly, results from failure of complete migration and fusion of the ventral bud, potentially causing duodenal obstruction.

Pancreatic embryology and duct formation

High‑Yield Points - ⚡ Biggest Takeaways

  • Head of pancreas in duodenal C-loop; tail at splenic hilum.
  • Main duct (Wirsung) joins CBD at ampulla of Vater; regulated by sphincter of Oddi.
  • Accessory duct (Santorini) opens at minor papilla, superior to major.
  • Arterial supply: Celiac trunk (gastroduodenal, splenic arteries) & SMA (inferior pancreaticoduodenal).
  • Endocrine: Islets produce Insulin (β-cells), Glucagon (α-cells), Somatostatin (δ-cells).
  • Exocrine: Acinar cells secrete digestive zymogens (amylase, lipase, proteases).
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Practice Questions: Pancreatic Anatomy and Physiology

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CT scan of abdomen showing a structure branching within the liver. Identify the structure.

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Flashcards: Pancreatic Anatomy and Physiology

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Carcinomas situated in the _____ of the pancreas are usually larger than the head

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Carcinomas situated in the _____ of the pancreas are usually larger than the head

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