The Islets of Langerhans are located in the pancreas. They are weirdly shaped patches of endocrine tissue throughout the pancreas of most vertebrates, including humans. They were first described by Dr. Paul Langerhans, a German physician, in 1869 and bear his name. A healthy human pancreas contains about 1 million islets, composed of four cell types, three of which produce hormones and the fourth, which still has no known function. Insulin is produced by one of these cells, essential to our bodies.