Circadian Rhythms

The word circadian comes from the Latin root circania meaning circle. For modern purposes, the word circadian refers to anything that occurs in 24 cycles or periods. Rest and activity, taking in of fluid, formation of urine, body temperature, cardiac output, oxygen consumption, cell division, and the secreting activity of endocrine glands all participate in 24 hour cycles in many organisms, and are referred to as circadian rhythms. One of the most well understood circadian rhythms is the sleep circadian rhythm. The circadian rhythm, commonly known as the biological clock, is thought to have three components, including the genetic machinery that allows the clock to regulate the expression of specific genes, the timekeeping machinery of the clock, and receptors that collect input from the outside world to set the clock.
Melatonin, the primary product of the pineal gland, has been known to regulate sleep cycles during the night for some time now. Just recently, scientists have discover...