Fig. 1.

Insulin action on multiple tissues. Insulin is primarily produced by the β cells of the pancreatic islets and secreted in response to glucose. In addition, food consumption promotes intestinal secretion of GLP-1, which acts on the β cells to enhance insulin release. Insulin release may also be modulated by the vagus nerve. Insulin acts on multiple tissues to regulate glucose metabolism. It stimulates glucose uptake and utilization in the muscle, while suppressing hepatic glucose release. Insulin promotes lipogenesis and suppresses lipolysis in the adipose tissue. While the effect of insulin action in the brain on appetite control is known, it may not play a significant role in glucose uptake. Insulin action on neuroprotection and cognitive function are being recognized recently