Chorion - wikipedia Chorion For the entertainment company, see Chorion ( company ). Chorion Diagram showing the chorion of a chicken egg Human fetus, enclosed in the amnion Details Identifiers Latin chorion MeSH D002823 TE E5. 11.3. 1.1. 0.3 Anatomical terminology ( edit on Wikidata ) The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles. It develops from an outer fold on the surface of the yolk sac, which lies outside the zona pellucida ( in mammals ), known as the vitelline membrane in other animals. In insects it is developed by the follicle cells while the egg is in the ovary. The main function of the chorion is to protect and nurture the embryo. Contents 1 Structure 1.1 Layers 1.2 Growth 1.3 Parts 1.4 Monochorionic twins 2 Other animals 2.1 Additional images 3 See also 4 References 5 External links Structure In humans and other mammals ( excluding monotremes ), the chorion is one of the fetal membranes that exist during pregnancy between the developing fetus and mother. The chorion and the amnion together form the amniotic sac. It is formed by extraembryonic mesoderm and the two layers of trophoblast that surround the embryo and other membranes. The chorionic villi emerge from the chorion, invade the endometrium, and allow the transfer of nutrients from maternal blood to fetal blood. Layers The chorion consists of two layers : an outer formed by the trophoblast, and an inner formed by the somatic mesoderm ; the amnion is in contact with the latter. 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. Growth The chorion undergoes rapid proliferation and forms numerous processes, the chorionic villi, which invade and destroy the uterine decidua, while simultaneously absorbing nutritive materials from it for the growth of the embryo. The chorionic villi are at first small and non-vascular, and consist of the trophoblast only, but they increase in size and ramify, whereas the mesoderm, carrying branches of the umbilical vessels, grows into them, and they are vascularized. Blood is carried to the villi by the paired umbilical arteries, which branch into chorionic arteries and enter the chorionic villi as cotyledon arteries. After circulating through the capillaries of the villi, the blood is returned to the embryo by the umbilical vein. 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. Parts The part of the chorion that is in contact with the decidua capsularis undergoes atrophy, so that by the fourth month scarcely a trace of the villi is left. This part of the chorion becomes smooth, and is named the chorion laeve ( from the Latin word levis, meaning smooth ). As it takes no share in the formation of the placenta, this is also named the non-placental part of the chorion. As the chorion grows, the chorion laeve comes in contact with the decidua parietalis and these layers fuse. The villi at the embryonic pole, which is in contact with the decidua basalis, increase greatly in size and complexity, and hence this part is named the chorion frondosum. Thus the placenta develops from the chorion frondosum and the decidua basalis. Monochorionic twins Main article : Monochorionic twins Monochorionic twins are twins that share the same placenta. This occurs in 0.3 % of all pregnancies, and in 75 % of monozygotic ( identical ) twins, when the split takes place on or after the third day after fertilization. The remaining 25 % of monozygous twins become dichorionic diamniotic. The condition may affect any type of multiple birth, resulting in monochorionic multiples. Other animals Amniotic embryo. a = embryo, b = yolk, c = allantois, d = amnion, e = chorion In reptiles, birds, and monotremes, the chorion is one of the four extraembryonic membranes that make up the amniotic egg that provide for the nutrients and protection needed for the embryo 's survival. It is located inside the albumin, which is the white of the egg. It encloses the embryo and the rest of the embryonic system. The chorion is also present in insects. During growth and development of the embryo, there is an increased need for oxygen. To compensate for this, the chorion and the allantois fuse together to form the chorioallantoic membrane. Together these form a double membrane, which functions to remove carbon dioxide and to replenish oxygen through the porous shell. At the time of hatching, the fetus becomes detached from the chorion as it emerges from the shell. 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. See also Choriogenesis Chorioamnionitis, an inflammation of the chorion and amnion, usually due to bacterial infection. Chorionic hematoma Gestational trophoblastic disease, any abnormal proliferation of the trophoblasts, including choriocarcinoma, a highly invasive cancer. References This article incorporates text in the public domain from page 60 of the 20th edition of Gray 's Anatomy ( 1918 ) Jump up ^ Chapman, R.F. ( 1998 ) `` The insects : structure and function '', Section The egg and embryology. Previewed in Google Books ( 1 ) on 26 Sep 2009. Jump up ^ `` Chorion ''. biologydictionary.net. Retrieved 16 August 2017. Jump up ^ Cordero L, Franco A, Joy SD, O'shaughnessy RW ( December 2005 ). `` Monochorionic diamniotic infants without twin - to - twin transfusion syndrome ''. Journal of Perinatology. 25 ( 12 ) : 753 -- 8. doi : 10.1038 / sj. jp. 7211405. PMID 16281049. ^ Jump up to : Shulman, Lee S. ; van Vugt, John M.G. ( 2006 ). Prenatal medicine. Washington, DC : Taylor & Francis. p. 447. ISBN 0 - 8247 - 2844 - 0. External links Histology image : 19903loa -- Histology Learning System at Boston University -- `` Female Reproductive System : placenta, chorionic plate '' McGill Membranes of the fetus and embryo Embryo Trophoblast Cytotrophoblast Syncytiotrophoblast Intermediate trophoblast Allantois Decidua Decidual cells Chorionic villi / Intervillous space Amnion sac cavity Fetus Umbilical cord Umbilical artery Umbilical vein Wharton 's jelly Circulatory Placenta Chorion Other Blastocoel Heuser 's membrane Vitelline duct Gestational sac Development of the circulatory system Heart Tubular heart Truncus arteriosus Bulbus cordis Primitive ventricle Primitive atrium Sinus venosus Chamber formation Atrioventricular Primary interventricular foramen Endocardial cushions Septum intermedium Atrioventricular canal Atrial Septum primum Foramen secundum Primary interatrial foramen Septum secundum Foramen ovale Other Aorticopulmonary septum Protein signalling in heart development Vessels Arteries Dorsal aorta Aortic arches Aortic sac Veins Anterior cardinal vein Posterior cardinal vein Common cardinal veins Lymph vessels Lymph sacs Extraembryonic hemangiogenesis Blood islands Chorion Connecting stalk Yolk sac Placenta Fetal circulation umbilical cord : Umbilical vein → Ductus venosus → Inferior vena cava → Heart → Pulmonary artery → Ductus arteriosus → Aorta → Umbilical artery yolk sac : Vitelline veins Vitelline arteries Anatomy portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Chorion&oldid=828229976 '' Categories : Wikipedia articles incorporating text from the 20th edition of Gray 's Anatomy ( 1918 ) Embryology Hidden categories : Pages with unresolved properties Talk Contents About Wikipedia Bosanski Català Čeština Deutsch Eesti Español فارسی Français Հայերեն Hrvatski Italiano ქართული Lietuvių Nederlands Polski Português Русский Српски / srpski Srpskohrvatski / српскохрватски Svenska Українська 13 more Edit links This page was last edited on 1 March 2018, at 09 : 22. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: the extraembryonic membrane that helps in the formation of the placenta is the
Answer: chorion