Islets of Langerhans

The endocrine (i.e., hormone-producing) cells of the pancreas are grouped in the islets of Langerhans. Discovered in 1869 by the German pathological anatomist Paul Langerhans, the islets of Langerhans constitute approximately 1 to 2% of the mass of the pancreas. There are about one million islets in a healthy adult human pancreas, which are interspersed evenly throughout the organ, and their combined weight is 1 to 1.5 grams. Each islet contains approximately one thousand cells and is 50-500 μm in diameter.

Cell types
Hormones produced in the Islets of Langerhans are secreted directly into the blood flow by (at least) four different types of cells:
 * Beta cells producing Insulin and Amylin (65-80% of the islet cells)
 * Alpha cells releasing Glucagon (15-20%)
 * Delta cells producing Somatostatin (3-10%)
 * PP cells containing polypeptide (1%)

Islets can influence each other through paracrine and autocrine communication, and beta-cells are coupled electrically to beta-cells (but not to other cell-types).

Paracrine feedback
The paracrine feedback system of the islets of Langerhans has the following structure:
 * Insulin: Activates beta cells and inhibits alpha cells.
 * Glucagon: Activates alpha which activates beta cells and delta cells.
 * Somatostatin: Inhibits alpha cells and beta cells.

Electrical activity
Electrical activity of pancreatic islets has been studied using patch clamp techniques, and it has turned out that the behavior of cells in intact islets differs significantly from the behaviour of dispersed cells.

As a treatment for type I diabetes
Since the islets of Langerhans are destroyed in type I diabetes, clinicians and researchers are actively pursuing islet transplantation technology as a means of curing this disease.

References in pop culture

 * A Harlan Ellison short story titled "Adrift Just Off the Islets of Langerhans: Latitude 38° 54' N, Longitude 77° 00' 13" W" appears in his collection Deathbird Stories. (Those coordinates locate the intersection of H and 2nd N.E. in Washington, D.C., behind Union Station)
 * American parodist "Weird Al" Yankovic released a song entitled Pancreas on his album Straight Outta Lynwood, which continually repeats the lyrics "Insulin, Glucagon, comin' from the Islets of Langerhans" to a catchy tune during the final minute of the song.
 * On their comedy album How Can You Be in Two Places at Once When You're Not Anywhere at All, The Firesign Theatre referred to immigrants who came "from little towns with strange names like Smegma, Spasmodic, Frog, and the far-flung Isles of Langerhans".