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Portrait of Islets of Langerhans

Anatomy · Glands & the immune system

Islets of Langerhans

Described by Paul Langerhans in 1869

Endocrine system · scattered through the pancreas

Small round clusters of hormone-making cells scattered like islands through the pancreas, whose bulk is a digestive gland. There are around a million of them in an adult, yet together they make up only one or two per cent of the organ. Beta cells make insulin, alpha cells glucagon, delta cells somatostatin and PP cells pancreatic polypeptide; together they keep blood glucose steady. They were found in 1869 by a Berlin medical student, Paul Langerhans, who did not know what they did.

How to spot them

  • ▸Pale-staining, roughly round clusters of cells surrounded by darker, grainy, enzyme-making acini
  • ▸Packed with capillaries, giving a richer blood supply per gram than the surrounding tissue
  • ▸More numerous in the tail of the pancreas than the head
  • ▸Made of several cell types: mostly beta cells, plus alpha, delta and PP cells
  • ▸Easy to miss in a slide of the pancreas until you look for the paler islands in the pink sea

What to know

Around a million pale cell clusters dotted through a digestive gland, together only 1–2% of its mass

Islets of Langerhans — the endocrine part of the pancreas.

Discovered in 1869 by a German medical student in his doctoral thesis, who did not know their purpose (1869)

Islets of Langerhans — Paul Langerhans; Édouard Laguesse named them in 1893.

Beta cells here release the only hormone that lowers blood glucose

Islets of Langerhans — insulin.

Alpha cells here make the hormone that raises blood glucose between meals

Islets of Langerhans — glucagon.

Their autoimmune destruction causes type 1 diabetes

Islets of Langerhans — the beta cells are attacked.

Transplanting these from a donor gave the 'Edmonton protocol' for hard-to-control diabetes in 2000 (2000)

Islets of Langerhans — islet transplantation, first reported from Edmonton, Canada.

Von Mering and Minkowski's dogs in 1889 became diabetic when the organ that holds these was removed (1889)

Islets of Langerhans — the link between pancreas and diabetes.

Key ideas

  • Beta cells sense glucose directly: as blood glucose rises, they take it up, their metabolism closes potassium channels, calcium enters and insulin granules are released.
  • Alpha and beta cells act as opposites: insulin lowers blood glucose by pushing it into cells; glucagon raises it by making the liver release stored glucose.

Quick-fire facts

  • •Roughly one million islets in a human pancreas; each is about 100–200 micrometres across
  • •They form only about 1–2% of the pancreas by mass but receive a much larger share of its blood flow
  • •Beta cells are the majority of an islet — roughly half to three-quarters, depending on the source — and alpha cells about a fifth
  • •Delta cells (about 4%) make somatostatin, which restrains both insulin and glucagon
  • •PP cells make pancreatic polypeptide; epsilon cells (rare) make ghrelin
  • •Paul Langerhans (1847–1888) described them as a 21-year-old student in Berlin, as 'islands of clear cells' he could not explain
  • •Frederick Banting and John Macleod shared the 1923 Nobel Prize in Physiology or Medicine for the discovery of insulin
  • •In type 1 diabetes the beta cells are destroyed by the immune system; in type 2 they fail to keep pace with insulin resistance

Drill it — 8 cards

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Sources