chorion

Examples of chorion in the following topics:

• Development of the Extraembryonic Coelom

  • The extra-embryonic coelom is a cavity that contains the chorion.
  • The extra-embryonic coelomic cavity is also called the chorionic cavity—it is enclosed by the chorionic plate.
  • It is the fetal aspect of the placenta that gives rise to chorionic villi.
  • The chorion is one of the membranes that exist during pregnancy between the developing fetus and the mother.
  • Blood is carried to the villi by the paired umbilical arteries, which branch into chorionic arteries and enter the chorionic villi as cotyledon arteries.

• Chorionic Villi and Placental Development

  • In the placenta, chorionic villi develop to maximize surface-area contact with the maternal blood for nutrient and gas exchange.
  • Chorionic villi sprout from the chorion after their rapid proliferation in order to give a maximum area of contact with the maternal blood.
  • During the primary stage (the end of fourth week), the chorionic villi are small, nonvascular, and contain only the trophoblast.
  • Chorionic villi are vital in pregnancy from a histomorphologic perspective and are, by definition, products of conception.
  • Image illustrating the placenta and chorionic villi.

• Implantation

  • The syncytiotrophoblast then implants the blastocyst into the endometrium of the uterus by forming finger-like projections into the uterine wall called chorionic villi.
  • The chorionic villi grow outwards until they come into contact with the maternal blood supply.
  • The creation of chorionic villi is assisted by hydrolytic enzymes that erode the uterine epithelium.
  • Human chorionic gonadotropin is the hormone that is detected by pregnancy tests, as it is found in the maternal bloodstream and urine.
  • During implantation, extensions of the trophoblast, the syncytiotrophoblasts, embed within the endometrium and form chorionic villi.

• Characteristics of Amniotes

  • However, the eggs of amniotes contain three additional extra-embryonic membranes: the chorion, amnion, and allantois.
  • While the inner amniotic membrane surrounds the embryo itself, the chorion surrounds the embryo and yolk sac.
  • The chorion facilitates exchange of oxygen and carbon dioxide between the embryo and the egg's external environment.
  • The key features of an amniotic egg are the chorion, amnion, and allantois.

• Fourth Week of Development

  • The chorion 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.
  • 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.

• Early Pregnancy Tests

  • ., human chorionic gonadotropin (hCG).
  • The first of these markers to be discovered, human chorionic gonadotropin (hCG), is produced by the trophoblast cells of the fertilized ovum (blastocyst).
  • Most chemical tests for pregnancy look for the presence of the beta subunit of hCG or human chorionic gonadotropin in the blood or urine. hCG can be detected in urine or blood after implantation, which occurs six to 12 days after fertilization.

• Amnion Development

  • Outside the amniotic ectoderm is a thin layer of mesoderm (continuous with that of the somatopleure), which is connected by the body stalk with the mesodermal lining of the chorion.
  • This fluid increases in quantity, causing the amnion to expand and ultimately to adhere to the inner surface of the chorion so that the extra-embryonic part of the coelom is obliterated.

• Prenatal Diagnostic Tests

  • ., amniocentesis (that can be done from about 14 weeks gestation up to about 20 weeks), and chorionic villus sampling (that can be done earlier: between 9.5 and 12.5 weeks gestation).
  • Chorionic villus sampling is associated with slightly more risk to the fetus.
  • Since chorionic villus sampling is performed earlier in the pregnancy than amniocentesis, typically during the first trimester, it can reasonably be expected that there will be a higher rate of miscarriage after chorionic villus sampling than after amniocentesis.
  • Because of the risk of miscarriage and fetal damage associated with amniocentesis and chorionic villus sampling procedures, many women prefer to first undergo screening so they can find out if the fetus' risk of birth defects is high enough to justify the risks of invasive testing.

• Placenta

  • The umbilical cord inserts into the chorionic plate of the placenta.
  • Human chorionic gonadotropin (hCG) is the first placental hormone produced, which can be found in maternal blood and urine as early as the first missed menstrual period (shortly after implantation has occurred) through about the hundredth day of pregnancy.

• Onset, Duration, and Half-Life of Hormone Activity

  • For instance, the biological half-life of luteinizing hormone is 20 minutes, which is shorter than that of a follicle-stimulating hormone (three to four hours), and of human chorionic gonadotropin (24 hours).