The primary function of the pineal gland is to secrete melatonin, which plays a role in regulating sleep cycles and in sexual development. The pineal gland also helps to regulate endocrine functions and to convert nervous signals into endocrine signals.
For many years, scientists and doctors have been confused about what the pineal gland actually does, long after discovering the functions of the rest of the endocrine organs. Scientists are not entirely sure of the full role that the pineal gland plays in the body, although they now believe that it mainly has to do with the secretion of melatonin, which is the only known hormone it produces.
Melatonin secretion is regulated by light, as the pineal gland produces high levels when it is dark and stops producing it when it is light.
The pineal gland has long been known as the "third eye," due to its location near the center of the brain. It is a small, reddish-gray organ that is shaped like a pine cone, and it is this shape that gives the pineal gland its name. As people age, the pineal gland often becomes calcified due to deposits of phosphorous, calcium and fluoride that build up over time.