FERNANDO DA CUNHA / BSIP / SCIENCE PHOTO LIBRARY FERNANDO DA CUNHA / BSIP / SCIENCE PHOTO LIBRARY
Melatonin is a hormone secreted by the pineal gland (red) at night. It regulates the body's daily biological rhythm depending on luminosity as light regulates its secretion via a path involving the suprachiasmatic nucleus (green), the paraventricular nucleus (yellow) and the preganglionic sympathetic neurons.
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