pineal gland

noun

variants or less commonly pineal or pineal body or pineal organ

: 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.

Example Sentences

Recent Examples on the Web These devices emit blue light, Dr. Alpert explains, which can interfere with the release of melatonin, a hormone produced in the brain's pineal gland that helps with sleep onset. —

Anna Kaufman, USA TODAY, 12 Jan. 2023 The pineal gland is a pea-sized body located deep in the brain. —

Neuroskeptic, Discover Magazine, 30 Sep. 2020 Melatonin is a hormone made by the pineal gland, which is located in the middle of the brain. —

Larry Carroll, Discover Magazine, 12 Oct. 2022 Melatonin is a brain chemical that is released by the pineal gland. —

Amber Smith, Discover Magazine, 13 Oct. 2022 Melatonin is naturally released from the pineal gland, located in the middle of the brain and helps regulate the circadian rhythm, or the body’s internal clock. —

Byalexa Mikhail, Fortune, 1 Nov. 2022 Certain authorities maintain that fluoride can negatively affect the pineal gland. —

Deborah Treisman, The New Yorker, 12 Sep. 2022 Melatonin is a naturally occurring hormone produced by the pineal gland that helps regulate the sleep-wake system. —

Elizabeth Chang, Washington Post, 20 June 2022 The pineal gland is located in the brain’s center region. —

The Salt Lake Tribune, 25 May 2022 See More

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.

Word History

First Known Use

1712, in the meaning defined above

Time Traveler

The first known use of pineal gland was in 1712

See more words from the same year

Cite this Entry

Style

“Pineal gland.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/pineal%20gland. Accessed 24 Mar. 2023.

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Kids Definition

pineal gland

noun

pi·ne·al gland

ˈpī-nē-əl,

pī-ˈnē-

: a small usually cone-shaped part of the brain of most vertebrates that has an eyelike structure in reptiles and produces melatonin especially in response to darkness

called also pineal body

Medical Definition

pineal gland

noun

: 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