Endocrine Pancreas, Islets of Langerhans

Examine these two sections of pancreas (sample 1, sample 2) and identify the islets of Langerhans, Islets range in size from 100-200 microns in diameter and contain few to several hundred cells, including alpha, beta, and delta cells that secrete glucagon, insulin, and somatostatin, respectively. Collectively, the islets constitute 1-2% of the total volume of the pancreas.

• At low magnification note the size, number, and distribution of islets within the pancreas.
• At higher magnification, note the histological differences between the exocrine and endocrine pancreatic tissues. Examine the distinctive acinar epithelium with its relatively intense eosinophilic and basophilic staining compared to the uniform, pale staining appearance of the epithelium in the islets. In routinely prepared H&E stained specimens, it is not possible to distinguish the alpha, beta, and delta cells of the islets as this requires special stains.
• Unlike the exocrine pancreas, endocrine glands do not use a ductal system to deliver their secretory products to their target sites. Rather, their secretory products (e.g. the endocrine hormones insulin, glucagon, and somatostatin) are taken up by nearby capillaries for delivery to their target tissues and organs throughout the body.

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