What is the Pineal Gland?

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

Sleep is essential for all of us, but difficult for some. For those who have trouble, sometimes the solution lies in resetting our internal clocks by retraining our pineal glands. This lesson defines the pineal gland, explains how essential its production of melatonin is, and outlines a possible secondary effect that melatonin has on the body.

Small, Yet Important

It's no secret that the human body is an amazing vessel. Thousands of organs, each with their own very specific function work in a harmony to which - unless something goes awry - we are mostly oblivious. While organs like the heart and the lungs and their functions are relatively well known, there are dozens of parts and pieces that go largely unnoticed, but are no less fascinating.

The pineal gland, for instance, is just one of those organs. The pineal gland is a very small gland located in the brain that is responsible for producing and releasing the hormone melatonin. While this sounds simple enough - after all, what is one hormone among the many that the body uses to regulate its processes? - this tiny little gland is so important it was once thought to be the source and very seat of the human soul!

Definition of the Pineal Gland

In the 17th century, the mathematician and philosopher Rene Descartes theorized that the soul itself resided in the pineal gland and that the tiny organ was the point of junction between the body and soul. Though science today does not support Descartes' opinion, it does agree with both the important function and mystery of the pineal gland.

The pineal gland is in the center of the brain.
Diagram of pineal gland

Not everything is known about the pineal gland. We do know that the gland is reddish-gray in color, small (about 5-8mm or 1/3 of an inch), and located in the epithalamus. The epithalamus is located roughly in the middle of the brain between the two hemispheres, at the rear-most part of the forebrain. If you were to isolate the pineal gland from the rest of the epithalamus, the tiny organ is pinecone-shaped; its shape is what gives the gland its name.

Gland's Function

We know for sure that the pineal gland performs at least one essential function - it is responsible for the production of the hormone melatonin. Not to be confused with melanin (which is pigment in the human body that gives hair and skin), melatonin is the hormone that helps determine your natural sleep-wake cycle, or circadian rhythm.

It may seem menial: a teeny, tiny organ makes one hormone, so what? But it's melatonin that allows you to feel naturally more sleepy at night, and the disruption of the production of melatonin that causes jet lag and has been linked to insomnia. It's rather impressive that an organ the size of a grain of rice has so much power over how well you are able to rest your body and when, and it's all dependant on light.

You see, the pineal gland releases melatonin in response to the presence or absence of light. The more light there is, the less melatonin is produced; the less light there is, the more melatonin is released. Putting it simply, when the eyes detect light, that information is translated by the hypothalamus (an area of the brain that serves to connect the nervous system to the endocrine system). The signal then travels down the spinal cord before being translated a second time by the superior cervical ganglia (a very special set of nerve groupings). The 'light is present' message is then sent back up the body and received by the pineal gland, which adjusts the amount of melatonin its producing accordingly.

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