The islets of Langerhans are clusters of cells in the pancreas that produce a variety of hormones. They are named for German pathologist Paul Langerhans, who first observed them in 1869. A healthy human pancreas contains approximately one million of these cells, but their total weight is only 1 to 1.5 grams (0.03 to 0.05 ounces), or about 1% of the weight of the pancreas. The rest of the pancreas serves to produce enzymes that aid in the digestion of food, while the islets of Langerhans produce hormones that help to regulate levels of sugar, also called glucose, in the blood.

Distributed throughout the pancreas, the islets of Langerhans are made up of at least five specific types of cells. The beta cells are the most prevalent, making up about 65 to 80% of the total islets. Beta cells are responsible for making the hormones insulin and amylin.

Insulin is the primary hormone involved in regulating the levels of glucose in the blood. It stores excess sugar in tissues in the form of glycogen, preventing blood levels of glucose from becoming too elevated. Damage to the insulin-producing beta cells in the islets of Langerhans is one of the primary causes of type 1 diabetes.

The beta cells in the islets of Langerhans also produce the hormone amylin. Amylin slows the emptying of the stomach after eating. It also works with insulin to limit the amount of glucose in the blood.

Alpha cells make up approximately 15 to 20% of the islets of Langerhans and produce the hormone glucagon. When blood glucose levels become too low, glucagon signals the liver to convert stored glycogen into glucose and release it into the bloodstream. Glucagon and insulin work against one another to keep blood glucose levels in check.

About 3 to 10% of the islets of Langerhans are made up of delta cells, which produce somatostatin. Somatostatin is not understood as well as insulin and some of the other hormones, but it is believed to slow emptying of the stomach, inhibit some gastrointestinal hormones, and work with glucagon against the release of too much insulin.

The remainder of the cells of the islets of Langerhans are made up of epsilon cells. These cells produce the hunger hormone ghrelin and pancreatic polypeptide (PP) cells, which regulate the secretions the pancreas makes. The functions of the epsilon and PP cells are not well understood.

Transplanting of cells from the islets of Langerhans has been explored as a possible way to control or even cure diabetes, especially type 1. Whole pancreas transplants have been successful, but are considered major surgeries with a variety of risks. Research continues to explore ways to transplant just the islets of Langerhans, which would bring similar benefits and fewer surgical risks for diabetic patients.