Pancreas - Exocrine pancreas

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Pancreas

Exocrine pancreas

Reviewer: Deepali Jain, M.D. (see Reviewers page)
Revised: 22 November 2012, last major update August 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● Acini comprise 80% of pancreas
● Composed of columnar to pyramidal epithelial cells with minimal stroma
● Basophilic due to prominent rough endoplasmic reticulum
● Have well developed Golgi complex
● Cells form apical oriented secretory complex with zymogen granules containing digestive enzymes (PAS+)
● After stimulation, zymogen granules migrate to apical plasma membrane and release contents into lumen
● Luminal border has prominent microvilli
● Centroacinar cells: in center of acini, occasionally in clusters, with pale cytoplasm and oval nuclei
● Intercalated duct: drains acini via intralobular ducts (cuboidal epithelium), to interlobular ducts lined by mucin secreting columnar cells

Physiology
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● Pancreas produces 2 liters/day of bicarbonate rich fluid containing digestive enzymes and proenzymes, regulated by neural stimulation (vagus nerve) and humoral factors (secretin, cholecystokinin)
● Pancreatic enzymes: trypsin, chymotrypsin, aminopeptidases, elastase, amylases, lipase, phospholipases, nucleases
● Cholecystokinin: promotes discharge of digestive enzymes by acinar cells; released from duodenum in response to fatty acids, peptides and amino acids
● Secretin: stimulates water and bicarbonate secretion by duct cells; is stimulated by acid from stomach and luminal fatty acids
● Trypsin: catalyzes activation of the other enzymes
● Pancreatic self-digestion: prevented by: packaging of most proteins as inactive proenzymes, enzyme sequestration in zymogen granules, proenzymes activated only by trypsin which is activated only by duodenal enterokinase, trypsin inhibitors are present in ductal and acinar secretions, intrapancreatic release of trypsin activates enzymes which degrade other digestive enzymes before they can destroy pancreas, lysosomal hydrolases can degrade zymogen granules to prevent auto destruction if acinar secretion is impaired, acinar cells themselves are highly resistant to trypsin, chymotrypsin and phospholipase A2

Micro images
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Acinar cells

Low power

Intercalary duct

Large excretory duct

Electron microscopy images
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Two centroacinar cells with electron-lucent cytoplasm, poor in organelles, surrounded by acinar cells rich in zymogen granules

Left: ductular cells with cell cytoplasm, some mitochondria, several elongated endosomes
Right: secondary interlobular duct has columnar cells containing juxtaluminal mucin granules with a homogeneous dense inner structure and irregularly distributed microvilli along the luminal borders

Pancreatic acinar cells

End of Pancreas > Exocrine pancreas

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