The Science of Diabetes
The Islets of Langerhans
(Endocrine cells of the pancreas)
Paul Langerhans (1847-1888)
Paul Langerhans was a German medical student writing has M.D. dissertation in Berlin in 1869. He was studying the pancreas and observed small collections of "clear cells" within the pancreas that appeared distinct from the surrounding pancreatic tissue.
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Figure
1. Diagram of the pancreas
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Figure 2. This is the pancreas as seen under a light microscope. In the center of the field is the Islet of Langerhans. The surrounding tissue is the part of the pancreas that makes digestive juices. |
It was known that the pancreas produced digestive enzymes, but Langerhnas could not guess what the function of these isolated cells was. 24 years later, in discussing the anatomy of the pancreas, Gustave-Edouard LaGuesse (1861-1922) referred to the "islet of Langerhans" and secured Paul Langerhans place in medical history.
Within the islets are 4 distinct types of cells. The terms alpha and beta cell were first used by M. A. Lane in 1907. The alpha cell produces glucagon. Glucagon raises blood sugar levels by releasing glucose stored in the liver as glycogen and causing glucose to be formed in the liver in a process called gluconeogenesis. Glucagon was identified in the A cell in 1962. The beta (ß) cell produces insulin. Insulin was identified in the B cell in 1938.
| Figure 3. This is a photomicrograph of an islet that has been stained to show the alpha cells containing glucagon on the left and the beta cells containing insulin on the right. |
A thid type of cell in the islet was observed by Dr. Shields Warren in his book Pathology of Diabetes (1930) and the cell was named the D or delta cell by Bloom in 1931. We now know that the D cell contains a hormone called somatostatin. Somatostin was identified in the D cell in 1975. Somatostatin is a smaller molecule that is also found in a part of the brain called the hypothalamus.
The fourth cell type is the PP cell which produces pancreatic polypeptide. PP is released along with insulin, but its function is not known. PP was identified in this cell in 1976.
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Figure
4. Diagram of the cells of the islet of Langerhans
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The electron microscope is a powerful tool that allows us to see the ultrastructure of cells. Islet cells have granules in them which contain the hormone of the cell. Different cells have different sized granules.
| Figure 5. Electron microscopic image of beta cell |
| Figure 6. A (alpha) cell granules containing glucagon |
| Figure 7. B (beta) cell granules containing insulin |
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Cells of the islet of Langerhans
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Cell type
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Hormone
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Size of granule
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A cell
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Glucagon
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200-300 nm
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B cell
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250-400 nm
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D cell
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Somatostatin
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150-400 nm
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PP cell
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Pancreatic polypeptide
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100-200 nm
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