Chorion

	WikiDoc Resources for Chorion
Articles
Most recent articles on Chorion Most cited articles on Chorion Review articles on Chorion Articles on Chorion in N Eng J Med, Lancet, BMJ
Media
Powerpoint slides on Chorion Images of Chorion Photos of Chorion Podcasts & MP3s on Chorion Videos on Chorion
Evidence Based Medicine
Cochrane Collaboration on Chorion Bandolier on Chorion TRIP on Chorion
Clinical Trials
Ongoing Trials on Chorion at Clinical Trials.gov Trial results on Chorion Clinical Trials on Chorion at Google
Guidelines / Policies / Govt
US National Guidelines Clearinghouse on Chorion NICE Guidance on Chorion NHS PRODIGY Guidance FDA on Chorion CDC on Chorion
Books
Books on Chorion
News
Chorion in the news Be alerted to news on Chorion News trends on Chorion
Commentary
Blogs on Chorion
Definitions
Definitions of Chorion
Patient Resources / Community
Patient resources on Chorion Discussion groups on Chorion Patient Handouts on Chorion Directions to Hospitals Treating Chorion Risk calculators and risk factors for Chorion
Healthcare Provider Resources
Symptoms of Chorion Causes & Risk Factors for Chorion Diagnostic studies for Chorion Treatment of Chorion
Continuing Medical Education (CME)
CME Programs on Chorion
International
Chorion en Espanol Chorion en Francais
Business
Chorion in the Marketplace Patents on Chorion
Experimental / Informatics
List of terms related to Chorion

Template:Infobox Anatomy

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The chorion surrounds the embryo and other membranes. It consists of two layers: an outer formed by the primitive ectoderm or trophoblast, and an inner by the somatic mesoderm; with this latter the amnion is in contact.

The trophoblast is made up of an internal layer of cubical or prismatic cells, the cytotrophoblast or layer of Langhans, and an external layer of richly nucleated protoplasm devoid of cell boundaries, the syncytiotrophoblast.

It undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua and at the same time absorb from it nutritive materials for the growth of the embryo.

The chorionic villi are at first small and non-vascular, and consist of trophoblast only, but they increase in size and ramify, while the mesoderm, carrying branches of the umbilical vessels, grows into them, and in this way they are vascularized.

Blood is carried to the villi by the branches of the umbilical arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the umbilical veins. Until about the end of the second month of pregnancy the villi cover the entire chorion, and are almost uniform in size, but after this they develop unequally.

The greater part of the chorion is in contact with the decidua capsularis, and over this portion the villi, with their contained vessels, undergo atrophy, so that by the fourth month scarcely a trace of them is left, and hence this part of the chorion becomes smooth, and is named the chorion læve; as it takes no share in the formation of the placenta, it is also named the non-placental part of the chorion.

On the other hand, the villi on that part of the chorion which is in contact with the decidua placentalis increase greatly in size and complexity, and hence this part is named the chorion frondosum.

Additional images

Section through the embryo.
Diagram illustrating early formation of allantois and differentiation of body-stalk.
Diagram showing later stage of allantoic development with commencing constriction of the yolk-sac.
Scheme of placental circulation.