pineal gland

noun
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

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, OrlandoSentinel.com, "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, NOLA.com, "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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More Definitions for pineal gland

pineal gland

noun

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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Britannica.com: Encyclopedia article about pineal gland

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