Figure 1.

Homeostasis of blood glucose is controlled by a complex network of interactions. Multiple signals from the pancreas and further away from the brain, liver, muscle, intestine, stomach, and adipose tissue regulate blood glucose homeostasis. Glucagon, insulin (together with amylin), pancreatic polypeptide, and somatostatin are produced by cells in the pancreatic islets. Islet cells emit insulin in response to high glucose, such as from food intake; this insulin is detected by numerous peripheral tissues, which then synthesize or induce several molecules/pathways, such as lipogenesis and gluconeogenesis, and block others, such as glycogenolysis. Importantly, insulin secretion can be regulated both locally and at a distance, for example, by hormones and incretins in the colon and the stomach. Blood glucose homeostasis can be regulated by endogenous hormones like glucocorticoids, which also display rhythmicity, and by exogenous variables like light exposure and food consumption, which modulate circadian rhythms.