How is the circadian system organized?
Using engineering parlance, the organization of the circadian system consists of three parts: (1) input system, (2) oscillator network, and (3) output system. The input system is represented by the retinal hypothalamic tract (RHT). The oscillatory network , itself with three parts, is represented by SCN, entrainment and tissue oscillators. The output system is represented by tissue-specific peripheral circadian outputs. For example, circadian outputs of muscle could be glucose uptake and oxidation; in the liver, they could be glucose uptake and production; in adipose tissue, the circadian outputs are lipolysis and lipogenesis; and in the pancreas, they are insulin and glucagon secretion. In fact, through different experimental sources, epidemiologic, clinical, and, especially, mammalian genetic study techniques, recent work has demonstrated exciting links of circadian disruption with T2DM pathophysiology and its treatment.