用戶:Zorro tnbz/sandbox

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File:Islet.png

A porcine islet of Langerhans. The left image is a brightfield image created using hematoxylin stain; nuclei are dark circles and the acinar pancreatic tissue is darker than the islet tissue. The right image is the same section stained by immunofluorescence against insulin, indicating beta cells.

Beta cells (beta-cells, β-cells) are a type of cell in the pancreas in areas called the islets of Langerhans. They make up 65-80% of the cells in the islets.

Function

Beta cells make and release insulin, a hormone that controls the level of glucose in the blood. There is a baseline level of glucose maintained by the liver, but it can respond quickly to spikes in blood glucose by releasing stored insulin while simultaneously producing more. The response time is fairly quick, taking approximately 10 minutes.

Apart from insulin, beta cells release C-peptide, a byproduct of insulin production, into the bloodstream in equimolar quantities. C-peptide helps to prevent neuropathy and other symptoms of diabetes related to vascular deterioration. Measuring the levels of C-peptide can give a practitioner an idea of the viable beta cell mass.

β-cells also produce amylin, also known as IAPP, islet amyloid polypeptide. Amylin functions as part of the endocrine pancreas and contributes to glycemic control. Amylin's metabolic function is now somewhat well characterized as an inhibitor of the appearance of nutrient [especially glucose] in the plasma. It thus functions as a synergistic partner to insulin. Whereas insulin regulates long term food intake, increased amylin decreases food intake in the short term.

Pathology

• Diabetes mellitus type 1 is caused by the destruction or dysfunction of insulin-producing beta cells by the cells of the immune system.

• In Diabetes mellitus type 2, by contrast, beta cells decline gradually over time, and insulin resistance plays at least as large a role in the disease

• Insulinoma is a rare tumor derived from beta cells. Insulinomas are usually benign and not malignant, but may be medically significant and even life-threatening due to recurrent and prolonged attacks of hypoglycemia.

Research

Much research is being done in the field of beta-cell physiology and pathology, focusing mostly on diabetes. Many researchers are trying to find ways to use these beta-cells to help control or prevent diabetes. A major topic is the replication of adult beta-cells and the application of these to diabetes. The Larry L. Hillblom Islet Research Center at UCLA is a leading research center in the field, within the Diabetes and Endocrinology Research Center, directed by Dr. Peter Butler.

A team science effort also exists, known as the Beta Cell Biology Consortium (BCBC). The BCBC is responsible for facilitating interdisciplinary approaches that will advance the understanding of pancreatic islet development and function. The long-term goal of the BCBC is to develop a cell-based therapy for insulin delivery.

In a study presented on June 8, 2008 at the American Diabetes Association’s 68th Scientific Sessions, a team showed that mice lacking insulin receptors in their beta cells had problems in the processing of insulin leading to excess, unprocessed levels of the hormone. Unprocessed insulin is unable to properly control glucose levels in the body. High circulating levels of unprocessed insulin and insulin resistance, a condition in which normal amounts of insulin are inadequate to produce a normal insulin response, are both known to be early indicators of type 2 diabetes.

See also

• insulin
• amylin
• C peptide
• Gastric inhibitory polypeptide receptor
• ATP-sensitive potassium channel
• List of terms associated with diabetes

External links

• 醫學主題詞表（MeSH）：Pancreatic+beta+cells