Pancreatic Islets (Islets of Langerhans)

The pancreatic islets, or islets of Langerhans, are the endocrine portion of the pancreas. Though they make up only a small fraction of the organ, they are the body's central regulators of blood glucose.

Structure and Location

The pancreas is a long gland lying behind the stomach, with most of its tissue dedicated to exocrine digestion (producing enzymes delivered to the intestine). Embedded throughout this exocrine tissue are roughly one to two million islets, microscopic clusters of endocrine cells that together account for only about 1-2% of the pancreas by mass. Islets are concentrated more heavily in the tail of the pancreas and are richly supplied with blood, receiving a disproportionately large share of pancreatic blood flow relative to their size.

Each islet contains several specialized cell types arranged in a characteristic pattern, often with a core of beta cells surrounded by a mantle of other cell types.

Key Functions

The islets contain at least four major endocrine cell types, each secreting a distinct hormone:

• Beta cells (the most abundant, roughly 65-80% of islet cells) produce insulin, which lowers blood glucose by helping cells take up sugar, and also secrete amylin.
• Alpha cells produce glucagon, which raises blood glucose by signaling the liver to release stored sugar.
• Delta cells produce somatostatin, which restrains the release of other hormones.
• PP (F) cells produce pancreatic polypeptide, involved in regulating digestion and appetite.

The opposing actions of insulin and glucagon keep blood sugar within a healthy range, a balance essential for steady energy supply to the brain and tissues.

Clinical Relevance

Disorders of the islets are central to diabetes mellitus. In type 1 diabetes, the immune system destroys beta cells, eliminating insulin production. In type 2 diabetes, tissues become resistant to insulin and beta-cell output eventually falls short. Rare islet-cell tumors such as insulinomas (excess insulin) or glucagonomas can also disrupt glucose control.

*This content is educational and not a substitute for professional medical advice.*