Insulin, we now know, is synthesized by a particular subset of islet cells in the pancreas—beta cells—and its secretion is stimulated by the presence of glucose in the blood. It then travels all over the body. Virtually every tissue responds to insulin: the presence of sugar means that the extraction of energy, and everything that flows from energy—the synthesis of proteins and fats, the storage of chemicals for future use, the firing of neurons, the growth of cells—can proceed. It is, perhaps, among the most important of the “long range” messages that acts as a central coordinator and
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