Figure 2.

Central and peripheral clocks. (a) The central clock, which is located in the suprachiasmatic nucleus, entrains environmental and endogenous cues. The most important signal is the light, which is transmitted to the SCN through the retina and the retinohypothalamic tract. The SCN then synchronises the peripheral clocks, found in all cells, via multiple direct and indirect routes; (b)The peripheral clocks, regulated by the central clocks, control the circadian rhythm of several systems, including the endocrine, gastrointestinal, cardiovascular and immune system. Abbreviations: CV cardiovascular, HDL high-density lipoprotein, SCN suprachiasmatic nucleus. For detailed explanation, please see [4] and references provided in the text.