Pancreatic islets

Pancreatic islets (Islets of Langerhans), are clusters of endocrine cells scattered throughout the exocrine pancreas that serve as the primary regulators of blood glucose homeostasis. They were first described by Paul Langerhans in 1869 and constitute approximately 12% of total pancreatic volume, with humans having roughly 13.2 million islets.

Darker-staining cells form clusters called acini, which are arranged in lobes separated by a thin fibrous barrier. The secretory cells of each acinus surround a small intercalated duct. Because of their secretory function, these cells have many small granules of zymogens that are visible. The intercalated ducts drains into larger ducts within the lobule, and finally interlobular ducts. The ducts are lined by a single layer of columnar cells. With increasing diameter, several layers of columnar cells may be seen.