Pancreas

THE PANCREAS IS a small organ in the abdomen that produces and secretes substances to aid digestion, as well as hormones that regulate the balance of blood sugar (glucose) levels. Recently, scientists have begun to characterize the stem cell population in the pancreas, but little is yet understood. A common disease associated with the pancreas is diabetes mellitus type I (DMI), an autoimmune disorder where a person's immune system attacks and destroys his or her own pancreatic islet cells, which produce and secrete insulin.

Pancreatic secretions are categorized as exocrine and endocrine. Exocrine secretions are released into ducts that connect to other organs, while endocrine secretions are hormonal and enter the bloodstream directly. The pancreas secretes the enzymes trypsin and chymotrypsin via ducts into the small intestine to aid in protein digestion, as well as pancreatic amylase for starch breakdown and pancreatic lipase for fat digestion. In addition, the pancreas secretes important hormones including glucagon and insulin. Glucagon and insulin have counteractive effects on blood sugar—glucagon stimulates the breakdown of sugar stores in the liver, raising blood sugar; in contrast, insulin stimulates cells to take up glucose, thus lowering blood sugar levels. Further hormones released by the pancreas are gastrin, somatostatin, and pancreatic polypeptide which act on additional organs. Therefore, the pancreas and its secretions affect multiple organ systems.

As with other organs, the pancreas has spécifie cancers. Pancreatic cancer falls into two main categories. The first type is an adenocarcinoma, or cancer of the epithelial cells. Epithelial cells line the body, both on the outside with skin, and inside such as the lining of the gastrointestinal tract and blood vessels. Adenocarcinomas are the majority of pancreatic cancers. For these cancers, the prognosis is poor. The minority of pancreatic cancers are in other cells such as the cells that produce insulin. These cancers generally have a better prognosis than adenocarcinomas.

A pancreatic disease with a potential stem cell—related cure is DMI. DMI has also been called juvenile onset diabetes, although this term is misleading because diabetes mellitus type II, also known as insulin—resistant diabetes, and sometimes adult onset diabetes, can also manifest in childhood. The result of both types of diabetes is an inability to control the levels of the sugar glucose in the blood, which can lead to devastating medical consequences. [Page 418]People with DMI have to take insulin shots several times daily; few people are able to have full pancreas transplants and in the case of a transplant 83 percent no longer need to take insulin. Although this transplant success rate is high, the availability of transplants is low compared to the prevalence of DMI. Given that only one cell type in the pancreas is affected in DMI, scientists believe it is possible to replace that cell type with stem cells and thereby cure DMI without the need for a full pancreatic transplant.

The first step is a better understanding of this cell type and how embryonic stem cells differentiate into cells. If researchers can determine the factors that induce development of the cells in an embryo, perhaps they can guide the differentiation of an embryonic stem cell into a pancreatic cell.

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