Amnion vs. Chorion — What's the Difference?
By Tayyaba Rehman & Urooj Arif — Updated on May 8, 2024
The amnion is the inner membrane surrounding the embryo, forming the amniotic sac, while the chorion is the outer membrane that encases the amnion and contributes to forming the placenta.
Difference Between Amnion and Chorion
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Key Differences
The amnion is a thin membrane that forms the protective amniotic sac around the embryo, providing cushioning and a stable environment. The chorion, on the other hand, is the thicker outermost membrane that envelops the amnion and aids in the development of the placenta.
The amnion contains the amniotic fluid, which cushions the embryo and maintains a consistent temperature. In contrast, the chorion plays a more structural role, anchoring to the uterine wall and forming the fetal portion of the placenta.
The amnion's primary function is to directly protect the embryo and help maintain a sterile, shock-absorbing environment. The chorion, however, facilitates nutrient and gas exchange through the placenta, crucial for the fetus's development.
During pregnancy, the amnion grows and stretches as the fetus develops. In comparison, the chorion also expands but focuses more on placenta formation, eventually merging with the amnion in later stages of pregnancy.
Comparison Chart
Position
Inner membrane, around the embryo
Outer membrane, encasing the amnion
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Role
Protective sac containing amniotic fluid
Supports placental development
Fluid Presence
Contains amniotic fluid
Generally lacks fluid
Function
Cushions and stabilizes the fetus
Anchors to the uterine wall and forms placenta
Growth
Expands to accommodate fetus
Expands, merging with amnion over time
Compare with Definitions
Amnion
An embryonic structure that grows as the fetus enlarges.
As the pregnancy progresses, the amnion expands to accommodate the fetus's growth.
Chorion
An important structure for placental development and fetal nourishment.
The chorion's villi form the fetal part of the placenta, which facilitates nutrient exchange.
Amnion
A layer that directly surrounds the embryo in early stages of pregnancy.
The amnion is vital for the embryo's early protection and growth.
Chorion
The outermost fetal membrane involved in placenta formation.
The chorion anchors the developing embryo to the uterine wall.
Amnion
A membrane that ensures a sterile environment for fetal development.
The amnion helps prevent infections by forming a sealed, sterile sac around the fetus.
Chorion
A thick membrane that surrounds the amnion and aids in nutrient exchange.
The chorion helps establish a connection between the mother and fetus for nutrient transfer.
Amnion
The inner fetal membrane that encloses the developing embryo.
The amnion forms the amniotic sac, which provides a protective environment for the fetus.
Chorion
An outer membrane that helps protect the embryo in early pregnancy.
The chorion covers the amnion and adds an extra layer of defense for the developing fetus.
Amnion
A thin membrane that holds the amniotic fluid around the fetus.
The amnion's fluid serves as a cushion to shield the fetus from external pressures.
Chorion
A membrane that expands during pregnancy to fully enclose the fetus.
The chorion gradually merges with the amnion as pregnancy advances.
Amnion
The amnion is a membrane that closely covers the human and various other embryos when first formed. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the developing embryo.
Chorion
The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). 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.
Amnion
A tough, thin membrane that forms a sac enclosing the embryo or fetus of a mammal, bird, or reptile. It is filled with a serous fluid in which the embryo or fetus is suspended.
Chorion
The outer membrane enclosing the embryo in reptiles, birds, and mammals. In placental mammals it contributes to the development of the placenta.
Amnion
(anatomy) The innermost membrane of the fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.
Chorion
The protective and nutritive membrane in higher vertebrates that attaches the fetus to the uterus.
Amnion
A thin membrane surrounding the embryos of mammals, birds, and reptiles.
Chorion
The outer case of an insect egg.
Amnion
Thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)
Chorion
(botany) The outer membrane of seeds of plants.
Chorion
The outer membrane which invests the fetus in the womb; also, the similar membrane investing many ova at certain stages of development.
Chorion
The outer membrane of seeds of plants.
Chorion
Outermost membranous sac enclosing the embryo in higher vertebrates (reptiles, birds and mammals)
Common Curiosities
What role does the chorion play in pregnancy?
The chorion contributes to the formation of the placenta, which is crucial for nutrient and gas exchange.
Is the amnion or the chorion closer to the embryo?
The amnion is closer, directly surrounding the embryo, while the chorion encloses the amnion.
Does the chorion form part of the placenta?
Yes, the chorion's villi develop into the fetal portion of the placenta.
Does the amnion contain any fluid?
Yes, the amnion contains the amniotic fluid that cushions and protects the embryo.
Which membrane provides immediate protection to the embryo?
The amnion provides immediate protection by creating a fluid-filled sac around the embryo.
Do the amnion and chorion merge during pregnancy?
Yes, they eventually merge, forming a combined amniochorionic membrane.
Does the amnion help regulate the fetal environment?
Yes, the amnion maintains a stable temperature and fluid environment for the fetus.
Does the amnion contribute to nutrient exchange?
Not directly; nutrient exchange occurs mainly through the placenta, which the chorion helps form.
Is the chorion visible on ultrasound scans?
Yes, especially in early pregnancy, it can be seen surrounding the amniotic sac.
Do identical twins share the same amnion or chorion?
They may share the same chorion but can have separate or shared amnions, depending on the timing of zygote splitting.
Can either the amnion or chorion rupture prematurely?
Yes, premature rupture can lead to complications like preterm birth or infections.
What happens to these membranes after birth?
They are expelled as part of the placenta and fetal membranes during childbirth.
Which membrane is critical for early pregnancy tests like chorionic villus sampling (CVS)?
The chorion, as the test collects chorionic villi for genetic testing.
How does the chorion assist in anchoring the fetus to the uterus?
The chorion's villi attach to the uterine wall, anchoring the placenta and securing the fetus.
Which membrane is more involved in shock absorption for the fetus?
The amnion, as it holds the amniotic fluid that cushions the fetus from shocks.
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Written by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Urooj ArifUrooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.
