pineal gland

variants: or less commonly pineal or pineal body or pineal organ

Definition of pineal gland

: a small, typically cone-shaped structure of the brain that arises from the roof of the third ventricle, is enclosed by the pia mater, and functions primarily as an endocrine gland secreting melatonin

Note: The pineal gland varies in morphological complexity, and in some nonmammalian vertebrates (such as various reptiles) may serve a photoreceptive function.

Examples of pineal gland in a Sentence

Recent Examples on the Web Infrared thermometers, which are held near the forehead to scan body temperature without direct contact, point an infrared light directly at the brain's pineal gland, exposing it to harmful radiation. Beatrice Dupuy, Star Tribune, "NOT REAL NEWS: A look at what happened this week," 31 July 2020 It is produced in the pea-size pineal gland, which is nestled in the middle of your brain and syncs melatonin production with the rising and setting of the sun. Anna Goldfarb, New York Times, "Considering Trying Melatonin for Sleep? Here’s a Guide to Help," 24 Apr. 2020 Melatonin, a hormone primarily secreted at night by the pineal gland, is a major driver of such changes. Jon Cohen, Science | AAAS, "Why do dozens of diseases wax and wane with the seasons—and will COVID-19?," 13 Mar. 2020 This portion of the brain instructs the pineal gland to secrete melatonin. John Schandelmeier, Anchorage Daily News, "Chemistry, not laziness, is why your couch beckons to you during the dark days of December," 21 Dec. 2019 Even when our eyes are closed, light can get through our eyelids’ thin skin, and reach the retina, which signals the pineal gland to stop making melatonin, a hormone that regulates sleep. Marni Jameson,, "5 steps to a healthier home," 4 Apr. 2018 Even when our eyes are closed, light can get through our eyelids' thin skin, and reach the retina, which signals the pineal gland to stop making melatonin, a hormone that regulates sleep. Contributing Writer,, "5 easy steps to a healthier home: From house plants to air filters," 2 Apr. 2018 The pineal gland emits melatonin in response to darkness. Lisa Alexia, Alaska Dispatch News, "Help our students with another hour of sleep," 12 Aug. 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'pineal gland.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of pineal gland

1712, in the meaning defined above

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The first known use of pineal gland was in 1712

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Cite this Entry

“Pineal gland.” Dictionary, Merriam-Webster, Accessed 25 Oct. 2020.

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More Definitions for pineal gland

pineal gland


Medical Definition of pineal gland

: a small body that arises from the roof of the third ventricle and is enclosed by the pia mater and that functions primarily as an endocrine gland that produces melatonin

called also pineal, pineal body, pineal organ

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