Final answer:
The pineal gland is responsible for releasing melatonin, a hormone that regulates the sleep-wake cycle, with production increasing during the night. Therefore, the correct answer to the question is C) Pineal.
Step-by-step explanation:
The gland responsible for releasing melatonin is the pineal gland. This tiny endocrine structure is situated in the diencephalon of the brain, specifically inferior and posterior to the thalamus. It is made up of cells known as pinealocytes, which produce and secrete melatonin primarily in response to low light levels or darkness.
Melatonin is crucial for regulating the sleep-wake cycle and can influence various biological rhythms, including circadian rhythms like sleep patterns and eating habits. In certain mammals, melatonin also plays a role in reproductive functions by affecting the production and maturation of reproductive organs and cells. Therefore, the correct answer to the question is C) Pineal.