yes it is
True
It would be an overstatement that a gland is responsible for sleep, however, the pineal gland does have some connection to sleep. It secretes a hormone called melatonin which contributes to sleepiness.
There is no adverb for sleepiness (tiredness). But there is an adverb for sleep, which is sleepily.
Want of sleep; inability to sleep; wakefulness; sleeplessness.
Pineal gland
the pineal gland
Pineal gland
Circadian
Pineal gland
melatonin
Circadian
no
Humans have a circadian rhythm that controls sleep and wakefulness.