Pineal gland

The pineal gland is a small, pine-cone-shaped endocrine gland located deep in the brain, near the center of the two hemispheres. It is best known for producing melatonin, a hormone derived from serotonin that regulates the sleep-wake cycle (circadian rhythm) and seasonal biological rhythms. Its secretion is inhibited by light detected by the retina, making it a crucial neuroendocrine transducer of light-dark information.