The Pineal Gland

The small pineal gland, located in the central part of the brain, is part of the endocrine system of the body. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both daily and seasonal cycles.

The shape of the gland resembles a pine cone from which it derived its name. It is located in the epithalamus, between the two hemispheres of the brain, tucked in a groove where the two halves of the thalamus join.

Melatonin production is stimulated by darkness and inhibited by light. It has input from the optic nerve system and is thought to act as a biological clock.

Interestingly, the pineal gland is does not share the obstruction of the blood-brain barrier with most of the brain in mammals. It has an abundant blood supply.

The human pineal gland grows in size until about 1-2 years of age, then remains stable except for some gradual increase in mass. The abundant melatonin levels in children are believed to inhibit early sexual development.