Question

melatonin is secreted by the
a pineal gland
b thyroid gland
c posterior pituitary
d hypothalamus

Explanation:

Melatonin is a hormone that regulates the sleep - wake cycle. The pineal gland is known to secrete melatonin. The thyroid gland secretes hormones like thyroxine and triiodothyronine. The posterior pituitary stores and releases hormones like oxytocin and vasopressin, not melatonin. The hypothalamus produces releasing and inhibiting hormones that regulate the pituitary gland, but it does not secrete melatonin.

Answer:

A. Pineal gland