Pronunciation: [kˈɔːɹi͡ən] (IPA) 
The word "chorion" is spelled with a "ch" at the beginning, as in "cherry". The "ch" sound is produced by pressing the tip of the tongue against the roof of the mouth and exhaling. The "o" in "chorion" is pronounced as a short vowel sound, similar to the "o" in "lot". The "r" in "chorion" is pronounced by vibrating the tongue against the roof of the mouth. The final "i" in "chorion" is pronounced as a long "e" sound, as in "bee".
The chorion is a specialized embryonic membrane found in reptiles, birds, and mammals, including humans. It is most commonly recognized as a crucial part of the placenta in mammals. The chorion forms an outer protective layer that surrounds the amniotic sac, fetus, and other embryonic structures. It is composed of a double layer of cells, with an outer layer called the trophoblast and an inner layer known as the somatic mesoderm.
The primary function of the chorion is to facilitate the exchange of gases, nutrients, and waste products between the fetus and the mother. It acts as a barrier that prevents harmful substances from reaching the developing fetus, while simultaneously allowing for the diffusion of essential substances. The trophoblast layer of the chorion plays a critical role in establishing the connection between the fetus and the mother's uterus, as it develops into chorionic villi. These finger-like projections increase the surface area available for exchange of substances and provide adherence to the uterine wall.
In humans, the chorion begins to form shortly after fertilization and becomes fully developed by around the ninth week of pregnancy. It plays a crucial role in supporting the growing embryo and facilitating its development by providing necessary nourishment and oxygen. Understanding the structure and function of the chorion contributes to our knowledge of embryology and placental development, allowing for better understanding and management of pregnancy-related complications.
The outermost of the fetal envelopes derived from the ovum.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.
The membrane investing the foetus in the womb; in bot., a fluid pulp composing the nucleus of the ovule in its earliest stage.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.
The word "chorion" originated from the Greek word "chórion" (χωρίον), which means "membrane" or "afterbirth". The Greek word derived from "choros" (χορός), meaning "space" or "boundary". In the context of biology, "chorion" refers to the outermost fetal membrane that surrounds the embryo in mammals, reptiles, and birds.
