Pancreatic Histology

  • The pancreas is formed from two basic tissue types termed the exocrine and endocrine pancreas. Although the exocrine and endocrine pancreas share a similar anatomic location, for all intensive purposes they are histologically and physiologically distinct. So too are the pathological processes which affect them.
Exocrine Pancreas
  • Architecture
    • The exocrine pancreas is architecturally analogous to salivary glands with a highly branched and lobulated ductal system that terminates in secretory acini. The smallest ducts which terminate in acini are referred to as intercalated ducts. Intercalated ducts merge into intralobular ducts which in turn merge into interlobular ducts. Interlobular ducts in turn drain into the main pancreatic duct which releases the secretions of the exocrine pancreas into the duodenum.
  • Cellular Components
    • Pancreatic Acinar Cells: These are plump, pyramidal cells that line the terminal pancreatic acini and primarily secrete pancreatic zymogens which are stored in characteristic cytosolic granules.
    • Pancreatic Ductal Cells: These are flat cells which line the pancreatic ducts and primarily secrete an aqueous bicarbonate-rich fluid.
Endocrine Pancreas
  • Cellular Components
    • The endocrine pancreas is formed from a collection of three functionally distinct polygonal cell types which can only be distinguished using special stains. These cell types have been given Greek alphabetical namesakes, Alpha Cells, Beta Cells, and Delta Cells, and secrete distinct peptide hormones. Alpha cells secrete glucagon, Beta cells secrete insulin, and Delta cells secrete somatostatin.
  • Architecture
    • The endocrine pancreas is diffusely scattered throughout the body of the pancreas in little balls of cells termed Islets of Langerhans. Islets of Langerhans make up about 2% of the total pancreatic mass and vary in size, being made up of a few hundred to few thousand endocrine cells. The Islets are highly vascular and are invested with a dense network of fenestrated capillaries. All three cell types are mixed together within the Islet although Alpha cells tend to be located toward the periphery. Beta cells compose about 60% of cells, about 25% are Alpha cells, while only 5% are Delta cells.