The chorion is the outermost membrane that encloses the embryo in reptiles, birds, and mammals. In mammals with a placenta, it plays a crucial role in placental formation.
Chorion: A Vital Fetal Membrane
The chorion develops from an outer fold on the surface of the yolk sac. It's a highly vascular membrane, meaning it contains a rich network of blood vessels. This vascularity is essential for its function in facilitating the exchange of gases and nutrients between the developing fetus and the mother (in placental mammals).
Key Roles of the Chorion:
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Placental Development (in placental mammals): The chorion contributes significantly to the formation of the placenta. It forms the fetal part of the placenta, connecting the fetus to the mother's uterus and enabling the transfer of oxygen, nutrients, and waste products. MedlinePlus Medical Encyclopedia Image shows how it forms the fetal side of the placenta.
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Protection: As the outermost membrane, the chorion provides a protective layer around the developing embryo.
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Gas and Nutrient Exchange: In placental mammals, the chorion's blood vessels facilitate efficient exchange of gases and nutrients with the mother's blood supply. Study.com highlights this key role.
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Other Roles: In non-placental species, the chorion plays different protective and developmental roles. For example, in fish, it forms an acellular envelope crucial for fertilization and early embryonic protection. ScienceDirect Topics
Clinical Significance:
The chorion is important in prenatal diagnostics. Chorionic villus sampling (CVS) is a prenatal test that involves taking a tissue sample from the chorion to detect chromosomal abnormalities and other genetic problems. Johns Hopkins Medicine describes this procedure. Conditions like a subchorionic hematoma, where blood collects beneath the chorion, can also have clinical significance during pregnancy. Cleveland Clinic explains this condition.
