pineal gland


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.

Examples of pineal gland in a Sentence

Recent Examples on the Web Melatonin is a hormone produced in the brain’s pineal gland that helps maintain our circadian rhythm—the 24-hour internal clock that regulates our sleep/wake cycles. Margaret Osborne, Smithsonian Magazine, 18 Dec. 2023 Part of the problem, said Khan, is the disruption of production of melatonin, a naturally occurring hormone that is secreted by the pineal gland in response to darkness. Cara Lynn Shultz, Peoplemag, 28 Aug. 2023 Secreted by the pineal gland, its presence in sufficient amounts is vital for the maintenance of a healthy sleep wake cycle. Amber Smith, Discover Magazine, 14 Aug. 2023 The pineal gland, which is located in the middle of the brain, does have a connection to sleep. Caitlin Pagán, Verywell Health, 11 July 2023 Melatonin is a hormone secreted by the pineal gland. Discover Magazine, 29 Apr. 2023 Instead, melatonin is a hormone that is made by the pineal gland, located deep within the brain, and released into the bloodstream to regulate the body’s sleep cycles. Sandee Lamotte, CNN, 25 Apr. 2023 It’s believed that the DMT found in ayahuasca activates the DMT naturally found in a person’s pineal gland, often considered the third eye portal amongst the spiritual set and Indigenous healers. Michaela Trimble, Condé Nast Traveler, 17 Jan. 2023 Melatonin is a hormone that is produced by the pineal gland in the brain. Amber Smith, Discover Magazine, 15 Dec. 2022

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'pineal gland.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1712, in the meaning defined above

Time Traveler
The first known use of pineal gland was in 1712

Dictionary Entries Near pineal gland

Cite this Entry

“Pineal gland.” Dictionary, Merriam-Webster, Accessed 22 Jul. 2024.

Kids Definition

pineal gland

pi·​ne·​al gland
: 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

: 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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