melatonin vs internal secretion

melatonin and internal secretion both are nouns.

Word	Noun	Adjective	Verb	Adverb
melatonin	Yes	No	No	No
internal secretion	Yes	No	No	No

As nouns, internal secretion is a hypernym of melatonin; that is, internal secretion is a word with a broader meaning than melatonin:

melatonin: hormone secreted by the pineal gland
internal secretion: the secretion of an endocrine gland that is transmitted by the blood to the tissue on which it has a specific effect

Other hypernyms of melatonin include endocrine, hormone.

melatonin (noun)	internal secretion (noun)
hormone secreted by the pineal gland	the secretion of an endocrine gland that is transmitted by the blood to the tissue on which it has a specific effect