During teen years, melatonin in pineal gland kicks in two hours later than any other stage of life. This is why teens sleep so much!
The pineal gland synthesizes and secretes melatonin, a structurally simple hormone that communicates information about environmental lighting to various parts of the body. Ultimately, melatonin has the ability to entrain biological rhythms and has important effects on reproductive function of many animals. The light-transducing ability of the pineal gland has led some to call the pineal the “third eye”.