melatonin(redirected from pineal hormone)
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Related to pineal hormone: thyroid hormone
melatonin:see pineal glandpineal gland
, small organ (about the size of a pea) situated in the brain. Long considered vestigial in humans, the structure, which is also called the pineal body or the epiphysis, is present in most vertebrates.
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A hormone secreted by the pineal gland that acts on melanophores in the skins of amphibians and reptiles to concentrate the melanin in the center of the cells, lightening the body surface; in higher vertebrates it conveys information about time that influences reproduction and circadian physiology.