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Questions and Answers
What are the two primary layers that form the bilaminar embryonic disc?
Which structure is formed by an extension of the hypoblast?
At the end of week 2 of development, the embryonic disk is composed of which of the following?
What kind of cells compose the outer layer of the trophoblast?
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What does the extraembryonic mesoderm differentiate into?
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Which type of mesoderm is formed from the hypoblast and cytotrophoblast?
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Which statement best describes the changes in the embryonic plate shape?
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What forms the roof, floor, and sides of the yolk sac?
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Which layer of the bilaminar embryonic disc is characterized by small cubical cells?
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What is the origin of the extra-embryonic mesoderm?
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What changes occur in the trophoblast during the early stages of development?
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Which change occurs to the shape of the bilaminar embryonic plate during development?
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Which structure appears around the 7th or 8th day of development?
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What do the isolated spaces within the extraembryonic mesoderm fuse to form?
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What defines the boundaries of the yolk sac?
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At the end of the first week of development, which structures comprise the blastocyst?
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Study Notes
Formation of the Bilaminar Disc
- Bilaminar disc develops by day 14 of embryonic development.
- Composed of two layers: epiblast (primary ectoderm) and hypoblast (primary endoderm).
- Initially formed from the inner cell mass of the blastocyst.
Changes in the Trophoblast
- Trophoblast differentiates into two layers due to mitotic division:
- Cytotrophoblast: inner, mononucleated cell layer.
- Syncytiotrophoblast: outer, multinucleated structure.
- Lacunae (isolated cavities) appear in syncytiotrophoblast, filling with maternal blood and forming intervillous spaces of the placenta.
Yolk Sac Formation
- Yolk sac develops from an extension of the hypoblast.
- Boundaries are defined by:
- Roof made of hypoblast.
- Floor and sides formed by Hauser's membrane.
Amniotic Sac Formation
- Amniotic sac arises from the epiblast and appears by day 7 or 8.
- Boundaries of the amniotic sac include:
- Roof and sides formed by amnioblast.
- Floor made of epiblast.
Formation of Extraembryonic Mesoderm
- Originates from hypoblast and cytotrophoblast.
- Extraembryonic mesoderm appears between the trophoblast and the primary yolk sac or amniotic cavity.
Extraembryonic Coelom Formation
- Spaces within the extraembryonic mesoderm rapidly fuse to create a large cavity known as the extraembryonic coelom.
Layers of Extraembryonic Mesoderm
- Extraembryonic mesoderm divides into two distinct layers (details not specified in the provided text, further study may be needed).
Formation of the Bilaminar Disc
- Bilaminar disc develops by day 14 of embryonic development.
- Composed of two layers: epiblast (primary ectoderm) and hypoblast (primary endoderm).
- Initially formed from the inner cell mass of the blastocyst.
Changes in the Trophoblast
- Trophoblast differentiates into two layers due to mitotic division:
- Cytotrophoblast: inner, mononucleated cell layer.
- Syncytiotrophoblast: outer, multinucleated structure.
- Lacunae (isolated cavities) appear in syncytiotrophoblast, filling with maternal blood and forming intervillous spaces of the placenta.
Yolk Sac Formation
- Yolk sac develops from an extension of the hypoblast.
- Boundaries are defined by:
- Roof made of hypoblast.
- Floor and sides formed by Hauser's membrane.
Amniotic Sac Formation
- Amniotic sac arises from the epiblast and appears by day 7 or 8.
- Boundaries of the amniotic sac include:
- Roof and sides formed by amnioblast.
- Floor made of epiblast.
Formation of Extraembryonic Mesoderm
- Originates from hypoblast and cytotrophoblast.
- Extraembryonic mesoderm appears between the trophoblast and the primary yolk sac or amniotic cavity.
Extraembryonic Coelom Formation
- Spaces within the extraembryonic mesoderm rapidly fuse to create a large cavity known as the extraembryonic coelom.
Layers of Extraembryonic Mesoderm
- Extraembryonic mesoderm divides into two distinct layers (details not specified in the provided text, further study may be needed).
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Description
This quiz covers the crucial developmental stages of the bilaminar disc, trophoblast changes, yolk sac, and amniotic sac formation. Gain insights into embryological development by exploring key concepts and terminology associated with these early structures. Perfect for students of developmental biology!
