Questions and Answers
What are the two distinct layers that the embryoblast separates into?
Which component of the trophoblast helps in maternal-fetal communication?
What is the initial function of the extraembryonic mesoderm?
What is the role of the placenta after the blastocyst is implanted?
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During implantation, what happens to the endometrial lining?
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What develops as part of the syncytiotrophoblast after implantation?
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What are the fluid-filled cavities that develop within the embryonic unit?
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What is the first week of gestation primarily concerned with in terms of embryonic development?
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What is the primary purpose of the trophoblast cells in the blastocyst?
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What important structure is established during the second week of development?
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What is formed on day eight of embryonic development?
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What happens to the zona pellucida during implantation?
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Which stage precedes the formation of the blastocyst?
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What mechanism allows the blastocyst to partially collapse during implantation?
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What is NOT a characteristic of the second week of development?
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Which of the following statements about the blastocyst is false?
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Study Notes
Second Week of Development
- Completion of implantation and establishment of fetomaternal interactions is a key feature during this week.
- Blastulation is the stage of early embryonic development resulting in the blastula, which later forms the blastocyst consisting of dividing cells (blastomeres).
- The blastocyst has an outer trophoblast layer that develops into the placenta and an inner cell mass (embryoblast) that forms the embryo.
Stages of Blastocyst Development
- By day eight of development, the inner cell mass differentiates into a bilaminar embryonic disc composed of two layers.
- The blastocyst partially collapses and changes shape to integrate into the endometrium due to the action of proteolytic enzymes from syncytiotrophoblast cells.
The Bilaminar Embryonic Disc
- Referred to as the week of twos due to the separation into two distinct layers: the embryoblast, extraembryonic mesoderm, and trophoblast.
- The embryoblast forms:
- Epiblast (upper layer)
- Hypoblast (lower layer)
- Two fluid-filled cavities develop: the amniotic cavity and the yolk sac.
- The trophoblast develops into two sub-layers:
- Cytotrophoblast
- Syncytiotrophoblast
Implantation
- Implantation is a critical biochemical and mechanical process spanning the first and second weeks of gestation.
- Following ovulation, the endometrial lining thickens, with elongated secretory glands and increased vascularity in preparation for embryo acceptance.
- Upon implantation, the placenta forms, connecting the embryo to the uterine wall.
- Syncytiotrophoblast forms vacuoles that fill with maternal blood, facilitating uteroplacental circulation as it erodes maternal capillaries and endometrial glands.
- Contents from endometrial glands are released into lacunae, contributing to the developing placenta.
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Description
This quiz covers essential concepts from the second week of embryonic development, focusing on implantation and fetomaternal interactions. Key processes like blastulation and the formation of the blastocyst are discussed, giving insights into early developmental stages.
