Definition

1. Noun:
   • The outermost fetal membrane in amniotes: The chorion is the outermost membranous sac that surrounds and protects the embryo or fetus in higher vertebrates, including reptiles, birds, and mammals. It plays a crucial role in gas exchange and, in mammals, contributes to the formation of the placenta.

Examples of Usage

• Noun:
  • In mammals, the chorion fuses with the allantois to form the chorioallantoic placenta.
  • The chorion is an essential extraembryonic membrane for embryonic development in birds.

Advanced Usage

• "Chorionic villus sampling (CVS)": A prenatal test where a sample of chorionic villi (finger-like projections from the chorion) is taken to diagnose genetic abnormalities.

  • The couple opted for chorionic villus sampling to check for chromosomal disorders.

• "Chorionic gonadotropin": A hormone, specifically human chorionic gonadotropin (hCG), produced by the chorion in early pregnancy.

  • A pregnancy test detects the presence of human chorionic gonadotropin in urine.

Variants and Related Words

• Chorionic (adj): Pertaining to the chorion.

  • Chorionic villi are critical for nutrient exchange.

• Chorioallantois (n): A structure formed by the fusion of the chorion and the allantois, especially in bird eggs and mammalian placentas.

Synonyms

• Extraembryonic membrane: A general term for membranes like the chorion, amnion, allantois, and yolk sac that support the embryo but are not part of its body.
• Fetal membrane: A membrane enclosing the fetus. (Note: This is a broader term that includes the chorion and amnion.)

Related Phrases

• "Chorion laeve": The smooth, non-villous part of the chorion in the human placenta.

  • The chorion laeve is the part of the chorion not involved in placental formation.

• "Chorion frondosum": The villous, bushy part of the chorion that forms the fetal portion of the placenta.

  • The chorion frondosum is the functional area for maternal-fetal exchange.

Noun

1. the outermost membranous sac enclosing the embryo in higher vertebrates (reptiles, birds and mammals)