11/1/2022 0 Comments Type to learn jr.3![]() In liver cells, an important function is to produce glucose (either by the breakdown of glycogen or de novo synthesis of glucose). In fat and muscle cells, glucose normally serves as an important source of energy which can be converted into fat or glycogen (as a form of stored energy) if necessary. These transporters increase glucose uptake into the cell. Insulin binds to a receptor for insulin in the plasma membrane of the cells in these tissues, and stimulates intracellular signaling pathways that ultimately cause the translocation of glucose transporters (GLUT4 in the case of fat and muscle cells) to the cell membrane. ![]() Important among these are fat, muscle, and liver. Subsequently, insulin circulates and acts on cells in a variety of tissues. This accumulation of calcium causes the secretion of insulin into the blood by particular cells in the islet called beta cells. As potassium channels close and cell depolarization increases, this causes calcium channels in the cell membrane to open and allow the flow of calcium into the cell. This, in turn, increases the ATP/ADP ratio, which results in closing of potassium channels in the cell membrane and subsequent depolarization of the cell. As glucose is taken up into beta cells, it is metabolized, which leads to an increased production of ATP. Glucose is taken up into pancreatic beta cells through a glucose transporter called GLUT2 (Figure 1). Multiple factors regulate the level of glucose in the blood, and central among these are insulin and glucagon. ![]() Given that, researchers are working to define the role of GPCRs in normal pancreatic islet physiology as well as in the pathophysiology of diabetes (Winzell & Ahren 2007).įollowing a meal, glucose levels in the blood circulation increase. GPCRs are a major class of receptors mediating extracellular messages to intracellular signaling pathways in islets, and, more importantly, have the potential to be drug targets. One particularly intriguing group of molecules involved in islet cell signaling is the G protein-coupled receptors (GPCRs). Although scientists have learned that glucose is the primary regulator of secretion in islets, a major focus of research in the field has been to define additional extracellular factors that regulate the secretion of both hormones, such as the hormone receptors and the intracellular signaling pathways they activate. These hormones are produced within specialized "islands" of cells in the pancreas called islets (or islets of Langerhans). Given the central role of these hormones in diabetes, scientists are seeking to understand their role in the physiology and pathophysiology of the control of blood glucose. Beyond insulin, the secretion of a second hormone, glucagon, may also be altered in diabetes. Physicians and researchers recognize that the defining characteristic of diabetes is low or absent insulin secretion and/or insulin signaling. Diabetes mellitus is a disease characterized by hyperglycemia (elevated glucose), which, because of its association with obesity, has become an epidemic in industrialized, first world societies. ![]()
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