GI hormones vs ghrelin

GI hormones and ghrelin both are nouns.

Word	Noun	Adjective	Verb	Adverb
GI hormones	Yes	No	No	No
ghrelin	Yes	No	No	No

As nouns, ghrelin is a hyponym of GI hormones; that is, ghrelin is a word with a more specific, narrower meaning than GI hormones:

GI hormones: hormones that affect gastrointestinal functioning
ghrelin: a gastrointestinal hormone produced by epithelial cells lining the fundus of the stomach; appears to be a stimulant for appetite and feeding, but is also a strong stimulant of growth hormone secretion from the anterior pituitary

Other hyponyms of GI hormones include gastrin, cholecystokinin, secretin, motilin.

GI hormones (noun)	ghrelin (noun)
hormones that affect gastrointestinal functioning	a gastrointestinal hormone produced by epithelial cells lining the fundus of the stomach; appears to be a stimulant for appetite and feeding, but is also a strong stimulant of growth hormone secretion from the anterior pituitary