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An islet cell is an insulin-secreting cell type located in the pancreas. These cells congregate in regions of the pancreas called the islets of Langerhans, where they produce several other hormones in addition to insulin. The cells are named after German scientist Paul Langerhans. In a healthy adult human pancreas, there are approximately one million islet cells, of which there are five known types.
The most prevalent type of islet cell in the pancreas is the beta cell. These are the cells that produce insulin, one of the principal hormones involved in maintaining healthy levels of blood sugar. Other islet cell types include alpha cells, which produce glucagon, somatostatin-producing delta cells, ghrelin-producing epsilon cells, and PP cells, which produce pancreatic polypeptide.
Each of these islet cell types produces hormones which work together with insulin to regulate the body's blood sugar and other systems. For example, glucagon increases blood sugar levels, and therefore has the exact opposite effect of insulin, which reduces blood sugar. The somatostatin produced by delta cells is involved in a number of pathways which act to limit the release of human growth hormone and regulate digestion. Ghrelin is a hunger-stimulating hormone, while pancreatic polypeptide is mainly involved in regulating the secretion of several pancreatic hormones.
One of the main diseases that can affect the islet cells of the pancreas is type 1 diabetes. This type of diabetes develops as a result of a type of immune system dysfunction called autoimmunity. A person with type 1 diabetes cannot produce insulin, because the immune system has attacked and destroyed all of the insulin-producing islet cells in the pancreas. Until recently, the only available medical treatment for type 1 diabetes has been close monitoring of blood sugar and diet, along with regular daily injections of insulin to keep blood sugar levels stable.
A new and potentially effective treatment for type 1 diabetes is called islet cell transplantation. In this treatment, beta islet cells from a deceased donor are transplanted into the liver or pancreas of a person with type 1 diabetes. If successful, this treatment can provide the patient with cells that can continue to produce a normal supply of insulin for a year or more. A person who receives donor cells must take immunosuppressive drugs to prevent transplant rejection by the immune system. Currently, this treatment is reserved mainly for people who are unable to control their blood sugar levels with insulin injections and dietary restriction, and who are at risk for severe hypoglycemic episodes.