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Pineal Gland | Location and Function

Pat Mccaw, Rebecca Gillaspy
  • Author
    Pat Mccaw

    Pat McCaw MD is a family physician and author. She earned her BS in Biology and MD in Medicine from the University of Iowa in 1998. She subsequently received her MFA in Creative Writing from Hamline University in 2016. She works part-time in family medicine while pursuing her love of writing. She has over 20 years of medical experience with an excellent grasp of the sciences, sociology, behavior, and emotional health. She writes middle grade and young adult fiction, and has experience with professional blog content from GILI Sports. She also maintains her own blog, Pat's Chat, and teaches online classes to educators on inventive ways to use picture books in the classroom to augment their curriculum, and fun exercises to teach creative writing.

  • Instructor
    Rebecca Gillaspy

    Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Learn about the pineal gland, its location, and the pineal gland's functions. See which hormone is secreted by the pineal gland and its importance in sleep. Updated: 01/20/2022

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Pineal Gland

The pineal gland definition is that of a small pea-sized organ within the brain that plays an important role in the endocrine system. It was the last organ of the body to be discovered and early researchers believed the pineal gland housed the soul. Although the soul and life's secrets are not hidden within the pineal gland, the gland secretes melatonin to regulate the body's circadian rhythms and normal sleep-wake cycle.

Researchers have studied the various roles that the pineal gland plays in development as well as in melatonin production. Different studies have suggested that the pineal gland can influence bone metabolism, mental health, puberty, and drug addiction. Pineal gland functions will be explored in more detail below.

Pineal Gland Location

The pineal gland's location influenced it being referred to as the "third eye." It is located at the midline of the brain between the two hemispheres (halves) of the brain. The pineal gland is also called the "pineal body" and is about the size of a pea. In Latin, "pinea" means pine cone, and the pineal gland was so named due to its pinecone shape.


The pineal gland is located between the right and left hemispheres of the brain.

The pineal gland is located between the right and left hemispheres of the brain.


The pineal gland weighs only 0.1 grams and is 5-9mm long. It is located between the two hemispheres of the brain at the midline and is composed of pinealocytes, endocrine cells that secrete melatonin. It is also composed of glial cells which are nerve cells that facilitate communication within the brain. Because the pineal gland is rich in calcium, it shows up well on an x-ray. Radiologists will use the pineal gland as a landmark on brain images to pinpoint the midline of the brain. The pineal gland is larger prior to puberty and its function decreases with age.

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  • 1:02 Melatonin
  • 2:01 Circadian Rhythm
  • 3:46 Seasonal Affective Disorder
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Pineal Gland Function

What does the pineal gland do? Its main function as an endocrine organ is to secrete the hormone melatonin. The pineal gland also plays a role in other bodily functions. These will be reviewed in detail below.

Hormone Secreted by the Pineal Gland

When asked which gland is responsible for releasing melatonin, the answer is the pineal gland. Melatonin is a hormone that plays a role in regulating circadian rhythms. Circadian rhythms manage the body's internal clock to make an individual feel drowsy, alert, or sleepy and to signal when they should wake up. Circadian rhythms are the twenty-four-hour cycle of bodily regulations that influence sleep and activity.


The pineal gland is responsible for the secretion of melatonin.

The pineal gland is responsible for the secretion of melatonin.


The hormone secreted by the pineal gland, melatonin, is released depending on the amount of light present. When there is more light present, melatonin secretion is inhibited to keep a person awake. When it is dark, more melatonin is secreted to promote drowsiness.


The pineal gland secretes melatonin which is important for restorative sleep.

The pineal gland secretes melatonin which is important for restorative sleep.


Melatonin's response to light explains why humans might become more sleepy after the sun goes down. If pineal gland sleep regulation is disrupted, supplemental melatonin is recommended to assist with sleep.

What Else Does the Pineal Gland Do?

In addition to melatonin production, the pineal gland plays a role in other regulatory processes in the body, as seen below:

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Frequently Asked Questions

What does the pineal gland do?

The main function of the pineal gland is to secrete the hormone melatonin. Melatonin plays a central role in a person's circadian rhythms and normal sleep-wake cycle.

The pineal gland is also associated with sexual development and maturation, bone metabolism, drug metabolism, and the aging process.

What is the function of melatonin?

Melatonin is secreted by the pineal gland and is a hormone that regulates circadian rhythms. More melatonin is produced in darkness to trigger drowsiness.

High melatonin levels may make a person drowsy while lower melatonin levels trigger someone to wake up from rest and to be more alert.

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