umbilical vesicle vs sac

umbilical vesicle and sac both are nouns.

Word	Noun	Adjective	Verb	Adverb
umbilical vesicle	Yes	No	No	No
sac	Yes	No	No	No

As nouns, sac is a hypernym of umbilical vesicle; that is, sac is a word with a broader meaning than umbilical vesicle:

umbilical vesicle: membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional
sac: a structure resembling a bag in an animal

umbilical vesicle (noun)	sac (noun)
membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional	a structure resembling a bag in an animal
	a case or sheath especially a pollen sac or moss capsule
	an enclosed space