Final answer:
The pineal gland releases the hormone melatonin.
Step-by-step explanation:
The pineal gland, located in the roof of the thalamus in the brain, releases the hormone melatonin. It is made up of pinealocytes, which produce and secrete melatonin in response to low light levels. high blood levels of melatonin induce drowsiness and help regulate the sleep-wake cycle.