( A ) The pineal gland is located on the dorsal side of midbrain.
( B ) Pineal secretes a hormone called melatonin.
( C ) melatonin influences metabolism, pigmentation, the menstrual cycle as well as our defense capability.
( D ) Melatonin plays a very important role in the regulation of a diurnal rhythm (sleep-wake cycle, rhytm of body temperature).
