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An Overview of the Pineal Gland

Maintaining Circadian Rhythym

For being such a tiny structure, the pineal gland has a colorful and misunderstood history. It’s considered a somewhat mysterious organ, as its function was discovered last of the endocrine glands.
The pineal gland was once dubbed the “third eye,” which originated for many reasons, ranging from its location deep in the center of the brain to its connection to light. Also, the French philosopher and mathematician René Descartes was fascinated with the pineal gland. He even regarded it as the “principal seat of the soul, and the place in which all our thoughts are formed.” However, his observations have been widely rejected1.
And while researchers are still learning about the full purpose of the pineal gland, they believe it most likely concerns melatonin—the only hormone that the gland is known to produce and release.

Pineal Gland Essentials

  • Of the endocrine organs, the function of the pineal gland was the last discovered.
  • Located deep in the center of the brain, the pineal gland was once known as the “third eye.”
  • The pineal gland produces melatonin, which helps maintain circadian rhythm and regulate reproductive hormones.
Anatomy of the Pineal Gland
Located near the center of the brain, the pineal gland is a very small organ shaped like a pine cone (which is where it gets its name). It’s reddish-gray and about 1/3 inch long. Pineal cells and neuroglial cells (which support the pineal cells) mainly comprise the gland.
The pineal gland often appears calcified in x-rays, which is usually due to fluoride, calcium, and phosphorus deposits that build up with age.
Melatonin: The Pineal Gland Hormone
The pineal gland secretes a single hormone—melatonin (not to be confused with the pigment melanin). This simple hormone is special because its secretion is dictated by light. Researchers have determined that melatonin has two primary functions in humans—to help control your circadian (or biological) rhythm and regulate certain reproductive hormones.
Circadian Rhythm
Your circadian rhythm is a 24-hour biological cycle characterized by sleep-wake patterns. Daylight and darkness help dictate your circadian rhythm. Light exposure stops the release of melatonin, and in turn, this helps control your circadian rhythms.
Melatonin secretion is low during the daylight hours and high during dark periods, which has some influence over your reaction to photoperiod (the length of day versus night). Naturally, photoperiod affects sleep patterns, but melatonin’s degree of impact over sleep patterns is disputed.
Melatonin blocks the secretion of gonadotropins (luteinizing hormone and follicle stimulating hormone) from the anterior pituitary gland. These hormones aid in the proper development and functioning of the ovaries and testes.

The pineal gland’s full purpose is still a bit of a mystery. But research suggests that we’re getting closer to understanding the pineal gland—and more about the endocrine system as a whole.