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During cleavage, the reduction in cell size serves primarily to optimize the surface area-to-volume ratio, facilitating more efficient nutrient exchange and waste removal despite a static cytoplasmic volume.
During cleavage, the reduction in cell size serves primarily to optimize the surface area-to-volume ratio, facilitating more efficient nutrient exchange and waste removal despite a static cytoplasmic volume.
False (B)
Cleavage divisions are uniquely characterized by the presence of both G1 and G2 phases within the cell cycle, allowing for significant cellular growth between each division.
Cleavage divisions are uniquely characterized by the presence of both G1 and G2 phases within the cell cycle, allowing for significant cellular growth between each division.
False (B)
The initiation of cleavage is contingent upon the complete degradation of maternal mRNAs and proteins, necessitating the zygote's reliance solely on its own newly transcribed genetic material.
The initiation of cleavage is contingent upon the complete degradation of maternal mRNAs and proteins, necessitating the zygote's reliance solely on its own newly transcribed genetic material.
False (B)
The zona pellucida actively promotes implantation by directing the developing conceptus toward the uterine wall through chemotactic signaling.
The zona pellucida actively promotes implantation by directing the developing conceptus toward the uterine wall through chemotactic signaling.
The progression through the two-cell and four-cell stages during cleavage is invariably synchronous, ensuring that all blastomeres divide at precisely the same rate.
The progression through the two-cell and four-cell stages during cleavage is invariably synchronous, ensuring that all blastomeres divide at precisely the same rate.
During the eight-cell stage, each blastomere is functionally restricted to forming only specific subsets of embryonic tissues due to the early segregation of lineage-specific determinants.
During the eight-cell stage, each blastomere is functionally restricted to forming only specific subsets of embryonic tissues due to the early segregation of lineage-specific determinants.
Compaction is driven primarily by the differential expression of cadherins, leading to increased cell adhesion and polarization but negligible changes in cellular morphology.
Compaction is driven primarily by the differential expression of cadherins, leading to increased cell adhesion and polarization but negligible changes in cellular morphology.
The morula's inner cell mass is uniquely defined by its ability to contribute to all three primary germ layers, as well as the germline, thus exhibiting 'totipotency'.
The morula's inner cell mass is uniquely defined by its ability to contribute to all three primary germ layers, as well as the germline, thus exhibiting 'totipotency'.
The trophoblast of the morula directly gives rise to the fetal component of the placenta, while the maternal component is derived exclusively from the inner cell mass.
The trophoblast of the morula directly gives rise to the fetal component of the placenta, while the maternal component is derived exclusively from the inner cell mass.
The transition from morula to blastocyst is characterized by the apoptotic elimination of the outer cell mass, facilitating the formation of the blastocoel.
The transition from morula to blastocyst is characterized by the apoptotic elimination of the outer cell mass, facilitating the formation of the blastocoel.
The blastocoel, being an inert cavity, serves primarily as a structural support for the developing embryo without contributing to cellular differentiation or signaling.
The blastocoel, being an inert cavity, serves primarily as a structural support for the developing embryo without contributing to cellular differentiation or signaling.
The parietal trophoblast, positioned over the embryoblast, secretes factors that inhibit differentiation of the underlying inner cell mass, maintaining its pluripotency.
The parietal trophoblast, positioned over the embryoblast, secretes factors that inhibit differentiation of the underlying inner cell mass, maintaining its pluripotency.
The abembryonic pole of the blastocyst initiates the process of implantation by forming direct cellular connections with the endometrial lining.
The abembryonic pole of the blastocyst initiates the process of implantation by forming direct cellular connections with the endometrial lining.
Uterine milk, a secretion rich in growth factors, is actively transported into the blastocoel via trophoblast-mediated transcytosis, promoting rapid expansion of the inner cell mass.
Uterine milk, a secretion rich in growth factors, is actively transported into the blastocoel via trophoblast-mediated transcytosis, promoting rapid expansion of the inner cell mass.
The embryoblast gives rise exclusively to the epiblast lineage, while the hypoblast is derived entirely from the trophoblast.
The embryoblast gives rise exclusively to the epiblast lineage, while the hypoblast is derived entirely from the trophoblast.
The primary role of the trophoblast is to facilitate nutrient transport to the developing embryo and it does not have a significant role in immune modulation at the maternal-fetal interface.
The primary role of the trophoblast is to facilitate nutrient transport to the developing embryo and it does not have a significant role in immune modulation at the maternal-fetal interface.
The blastocyst stage concludes precisely at the moment of complete implantation, defined by the full integration of the syncytiotrophoblast into the maternal decidua.
The blastocyst stage concludes precisely at the moment of complete implantation, defined by the full integration of the syncytiotrophoblast into the maternal decidua.
The formation of the blastocoel predominantly relies on active calcium ion expulsion from the inner cell mass, establishing an osmotic gradient that drives fluid influx.
The formation of the blastocoel predominantly relies on active calcium ion expulsion from the inner cell mass, establishing an osmotic gradient that drives fluid influx.
After the morula approaches the uterine cavity, the oocyte re-enters meiosis II to prevent the fusion of the blastomeres.
After the morula approaches the uterine cavity, the oocyte re-enters meiosis II to prevent the fusion of the blastomeres.
The mural trophoblast directly overlying the inner cell mass undergoes rapid proliferation and differentiation into the syncytiotrophoblast upon implantation.
The mural trophoblast directly overlying the inner cell mass undergoes rapid proliferation and differentiation into the syncytiotrophoblast upon implantation.
Flashcards
Cleavage
Cleavage
Rapid, repeated mitotic divisions in the zygote.
Purpose of Cleavage
Purpose of Cleavage
To reduce the size of the oocyte to that of a normal somatic cell, restoring the nuclear-cytoplasmic ratio.
Blastomeres
Blastomeres
Cells produced during cleavage.
Cleavage vs. Mitosis
Cleavage vs. Mitosis
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Cleavage Timing
Cleavage Timing
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Zona Pellucida's Role
Zona Pellucida's Role
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Early Cleavage Stages
Early Cleavage Stages
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Totipotency definition
Totipotency definition
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Pluripotency definition
Pluripotency definition
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Compaction
Compaction
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Morula
Morula
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Inner Cell Mass Function
Inner Cell Mass Function
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Trophoblast
Trophoblast
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Embryoblast
Embryoblast
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Blastocoel Formation
Blastocoel Formation
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Embryoblast Fate
Embryoblast Fate
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Trophoblast Fate
Trophoblast Fate
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Blastocele Fate
Blastocele Fate
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Embryonic pole (animal pole)
Embryonic pole (animal pole)
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Abembryonic pole
Abembryonic pole
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Study Notes
Overview of Cleavage
- Cleavage involves rapid, repeated mitotic divisions in the zygote.
- The purpose of cleavage is to reduce the size of the oocyte to that of a normal somatic cell,
- This process restores the normal nuclear-cytoplasmic ratio in the developing cells.
- The cells produced during cleavage are called blastomeres.
Differences Between Cleavage and Mitosis
- Mitosis does not decrease cell size, whereas cleavage does.
- Cleavage involves decreasing the cytoplasm during cell division.
Timing and Duration of Cleavage
- Cleavage begins immediately after fertilization, when the male and female pronuclei fuse.
- Cleavage continues until implantation, which occurs around the seventh day after fertilization.
- This means cleavage occurs throughout the entire first week of development.
The Role of the Zona Pellucida
- The zona pellucida prevents abnormal implantation of the developing conceptus in the fallopian tube i.e. ectopic pregnancy.
- Stages covered by the zona pellucida are considered part of the cleavage process, and when the zona pellucida disappears, implantation begins which marks the end of cleavage.
Stages of Cleavage
- Early stages include two-cell, three-cell, and four-cell stages.
- Unequal mitosis accounts for the three-cell stage, where one cell has more cytoplasm and divides first.
- Cleavage progresses in a pattern of 2, 4, 8, 16, 32, 64 cells, and so on.
Morula Stage
- At the eight-cell stage, cells are totipotent, meaning they can form both intra-embryonic and extra-embryonic tissues.
- Compaction is a process that occurs after the eight-cell stage where cells rearrange themselves.
- It leads to the formation of a 16-cell stage, known as the morula.
- The morula has two cell types: an outer cell mass and an inner cell mass.
- Inner cell mass is only responsible for forming derivatives of ectoderm, endoderm, and mesoderm.
- Cells in the inner cell mass are considered pluripotent, as they can only form body cells.
- Key features of the morula include:
- A 16-cell stage forms around the third day of fertilization.
- Cells are arranged into inner and outer cell masses.
- Inner cells are pluripotent, and outer cells forms trophoblasts.
- Still lined by the zona pellucida.
Blastocyst Stage
- As the morula approaches the uterine cavity, uterine fluid (uterine milk) enters the morula which contains nutrients.
- By day four, fluid enters between the cells of the inner cell mass.
- These fluid-filled spaces fuse, forming a large cavity called the blastocoel.
- The fluid pushes the inner cell mass to one end of the developing zygote.
- A blastocyst forms on the fourth day after fertilization.
- At this stage, cells around total 32 to 64.
- Parts of a Blastocyst include:
- The outer cell layer is called the trophoblast which are nutrition cells that form the placenta.
- The inner cell mass is called the embryoblast.
- The trophoblast is divided into polar trophoblast (covering the embryoblast) and mural trophoblast (remaining trophoblast).
- The embryonic pole (also known as the animal pole) is the area where the embryoblast is located, and it is the site where implantation begins.
- The abembryonic pole is the remaining area of the blastocyst.
- Fates of the different parts of the blastocyst:
- Embryoblast forms the tissues of the embryo,
- Trophoblast forms extra-embryonic tissue (placenta).
- Blastocele forms the yolk sac.
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