ISLETS OF LANGERHANS

Slide #144 - Pancreas - Most of the pancreatic tissue is comprised of enzyme-producing pancreatic ascinar cells.   Scattered among the ascini are pale, large rounded clusters of endocrine cells.   The clusters are known as the Islets of Langerhans .   Each islet is surrounded by a delicate connective tissue that separates it from the ascinar cells.   Similar to the ascinar cells, pancreatic islet cells are derived from the embryonic endoderm.   At least 4 secretory cell types are found in the islets of Langerhans: alpha cells secreting glucagon; beta cells secreting insulin; delta cells secreting somatostatin; and PP cells secreting pancreatic polypeptide, which inhibits pancreatic exocrine secretion.   However, you cannot distinguish the secretory cell types of the pancreas without special stains or immunohistochemistry with antibodies against individual hormones.   On high power, you may be able to appreciate the numerous capillaries within the Islets of Langerhans.