Final answer:
The pineal gland, found in the brain, produces melatonin which regulates the sleep-wake cycle. The pancreas contains cells that produce insulin and glucagon to maintain blood glucose levels.
Step-by-step explanation:
The pineal gland is a small endocrine gland located in the diencephalon of the brain, just posterior to the thalamus. It consists primarily of pinealocytes, which are responsible for producing the hormone melatonin. Melatonin plays a crucial role in regulating the sleep-wake cycle and is also involved in other circadian rhythms, such as eating patterns. The secretion of melatonin increases in response to darkness and decreases when it is bright, with signals being processed through the suprachiasmatic nucleus (SCN) of the hypothalamus, which then relays information to the pineal gland about the light-dark cycle.
The pancreas houses the islets of Langerhans, which contain endocrine cells including alpha and beta cells. Alpha cells produce glucagon, while beta cells produce insulin. These hormones have opposite effects on blood glucose levels: insulin lowers blood glucose by facilitating its uptake into cells, and glucagon raises it by stimulating the liver to release stored glucose. The balance between these hormones maintains normal blood glucose levels.