Canadian Medical Guide > Anatomy > Embryonic Structures > Embryo > Fetal Membranes Terms and Definitions

Fetal Membranes

Medical Definition:	Thin layers of tissue which surround the embryo or fetus and provide for its nutrition, respiration, excretion and protection; they are the yolk sac, allantois, amnion, and chorion.
Guide Notes:	mammalian only but specifics may be used with non-mammalian (e.g., CHICK EMBRYO); induced rupture = LABOR, INDUCED; premature rupture = FETAL MEMBRANES, PREMATURE RUPTURE; rupture in normal labor = FETAL MEMBRANES (IM) + LABOR (IM)

Fetal Membranes Categories.

	Allantois - An embryonic diverticulum of the hindgut of reptiles, birds, and mammals; in man its blood vessels give rise to those of the umbilical cord.
	Amnion - The extraembryonic membrane which contains the EMBRYO and AMNIOTIC FLUID.
	Chorion - The outermost extraembryonic membrane.
	Yolk Sac - An embryonic membrane formed from endoderm and mesoderm. In reptiles and birds it incorporates the yolk into the digestive tract for nourishing the embryo. In placental mammals its nutritional function is vestigial; however, it is the source of most of the intestinal mucosa and the site of formation of the germ cells. It is sometimes called the vitelline sac, which should not be confused with the vitelline membrane of the egg.

Fetal Membranes Medical Definitions and Terms

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