The endocrine (i.e. hormone-producing) cells of the pancreas are grouped in the so-called Islets of Langerhans. Discovered in 1869 by the German pathological anatomist Paul Langerhans (1847-1888), the Islets of Langerhans constitute 1-2% of the mass of the pancreas. Each islet contains a few thousand cells and is 0.2-0.5mm in diameter.
Hormones produced in the Islets of Langerhans are secreted directly into the blood flow by (at least) four different types of cells:
- 65-80% of the islet cells are insulin-producing beta-cells.
- The second most abundant cell type is the glucagon-releasing alpha-cells (15-20%).
- somatostatin-producing delta-cells (3-10%)
- and pancreatic polypeptide-containing PP-cells (1%).
The paracrine feed-back system of the Islets of Langerhans has the following structure:
Electrical activity of pancreatic islet-cells has been studied using the patch-clamp technique, and it has turned out that the behaviour of cells in intact islets differs significantly from the behaviour of dispersed cells.